Carter  Frami

Carter Frami

1621909571

2️⃣4️⃣ #30DaysofAppwrite : First Cloud Function using Dart

Let’s write our first cloud function using Dart.

#dart

What is GEEK

Buddha Community

2️⃣4️⃣ #30DaysofAppwrite : First Cloud Function using Dart
Chloe  Butler

Chloe Butler

1667425440

Pdf2gerb: Perl Script Converts PDF Files to Gerber format

pdf2gerb

Perl script converts PDF files to Gerber format

Pdf2Gerb generates Gerber 274X photoplotting and Excellon drill files from PDFs of a PCB. Up to three PDFs are used: the top copper layer, the bottom copper layer (for 2-sided PCBs), and an optional silk screen layer. The PDFs can be created directly from any PDF drawing software, or a PDF print driver can be used to capture the Print output if the drawing software does not directly support output to PDF.

The general workflow is as follows:

  1. Design the PCB using your favorite CAD or drawing software.
  2. Print the top and bottom copper and top silk screen layers to a PDF file.
  3. Run Pdf2Gerb on the PDFs to create Gerber and Excellon files.
  4. Use a Gerber viewer to double-check the output against the original PCB design.
  5. Make adjustments as needed.
  6. Submit the files to a PCB manufacturer.

Please note that Pdf2Gerb does NOT perform DRC (Design Rule Checks), as these will vary according to individual PCB manufacturer conventions and capabilities. Also note that Pdf2Gerb is not perfect, so the output files must always be checked before submitting them. As of version 1.6, Pdf2Gerb supports most PCB elements, such as round and square pads, round holes, traces, SMD pads, ground planes, no-fill areas, and panelization. However, because it interprets the graphical output of a Print function, there are limitations in what it can recognize (or there may be bugs).

See docs/Pdf2Gerb.pdf for install/setup, config, usage, and other info.


pdf2gerb_cfg.pm

#Pdf2Gerb config settings:
#Put this file in same folder/directory as pdf2gerb.pl itself (global settings),
#or copy to another folder/directory with PDFs if you want PCB-specific settings.
#There is only one user of this file, so we don't need a custom package or namespace.
#NOTE: all constants defined in here will be added to main namespace.
#package pdf2gerb_cfg;

use strict; #trap undef vars (easier debug)
use warnings; #other useful info (easier debug)


##############################################################################################
#configurable settings:
#change values here instead of in main pfg2gerb.pl file

use constant WANT_COLORS => ($^O !~ m/Win/); #ANSI colors no worky on Windows? this must be set < first DebugPrint() call

#just a little warning; set realistic expectations:
#DebugPrint("${\(CYAN)}Pdf2Gerb.pl ${\(VERSION)}, $^O O/S\n${\(YELLOW)}${\(BOLD)}${\(ITALIC)}This is EXPERIMENTAL software.  \nGerber files MAY CONTAIN ERRORS.  Please CHECK them before fabrication!${\(RESET)}", 0); #if WANT_DEBUG

use constant METRIC => FALSE; #set to TRUE for metric units (only affect final numbers in output files, not internal arithmetic)
use constant APERTURE_LIMIT => 0; #34; #max #apertures to use; generate warnings if too many apertures are used (0 to not check)
use constant DRILL_FMT => '2.4'; #'2.3'; #'2.4' is the default for PCB fab; change to '2.3' for CNC

use constant WANT_DEBUG => 0; #10; #level of debug wanted; higher == more, lower == less, 0 == none
use constant GERBER_DEBUG => 0; #level of debug to include in Gerber file; DON'T USE FOR FABRICATION
use constant WANT_STREAMS => FALSE; #TRUE; #save decompressed streams to files (for debug)
use constant WANT_ALLINPUT => FALSE; #TRUE; #save entire input stream (for debug ONLY)

#DebugPrint(sprintf("${\(CYAN)}DEBUG: stdout %d, gerber %d, want streams? %d, all input? %d, O/S: $^O, Perl: $]${\(RESET)}\n", WANT_DEBUG, GERBER_DEBUG, WANT_STREAMS, WANT_ALLINPUT), 1);
#DebugPrint(sprintf("max int = %d, min int = %d\n", MAXINT, MININT), 1); 

#define standard trace and pad sizes to reduce scaling or PDF rendering errors:
#This avoids weird aperture settings and replaces them with more standardized values.
#(I'm not sure how photoplotters handle strange sizes).
#Fewer choices here gives more accurate mapping in the final Gerber files.
#units are in inches
use constant TOOL_SIZES => #add more as desired
(
#round or square pads (> 0) and drills (< 0):
    .010, -.001,  #tiny pads for SMD; dummy drill size (too small for practical use, but needed so StandardTool will use this entry)
    .031, -.014,  #used for vias
    .041, -.020,  #smallest non-filled plated hole
    .051, -.025,
    .056, -.029,  #useful for IC pins
    .070, -.033,
    .075, -.040,  #heavier leads
#    .090, -.043,  #NOTE: 600 dpi is not high enough resolution to reliably distinguish between .043" and .046", so choose 1 of the 2 here
    .100, -.046,
    .115, -.052,
    .130, -.061,
    .140, -.067,
    .150, -.079,
    .175, -.088,
    .190, -.093,
    .200, -.100,
    .220, -.110,
    .160, -.125,  #useful for mounting holes
#some additional pad sizes without holes (repeat a previous hole size if you just want the pad size):
    .090, -.040,  #want a .090 pad option, but use dummy hole size
    .065, -.040, #.065 x .065 rect pad
    .035, -.040, #.035 x .065 rect pad
#traces:
    .001,  #too thin for real traces; use only for board outlines
    .006,  #minimum real trace width; mainly used for text
    .008,  #mainly used for mid-sized text, not traces
    .010,  #minimum recommended trace width for low-current signals
    .012,
    .015,  #moderate low-voltage current
    .020,  #heavier trace for power, ground (even if a lighter one is adequate)
    .025,
    .030,  #heavy-current traces; be careful with these ones!
    .040,
    .050,
    .060,
    .080,
    .100,
    .120,
);
#Areas larger than the values below will be filled with parallel lines:
#This cuts down on the number of aperture sizes used.
#Set to 0 to always use an aperture or drill, regardless of size.
use constant { MAX_APERTURE => max((TOOL_SIZES)) + .004, MAX_DRILL => -min((TOOL_SIZES)) + .004 }; #max aperture and drill sizes (plus a little tolerance)
#DebugPrint(sprintf("using %d standard tool sizes: %s, max aper %.3f, max drill %.3f\n", scalar((TOOL_SIZES)), join(", ", (TOOL_SIZES)), MAX_APERTURE, MAX_DRILL), 1);

#NOTE: Compare the PDF to the original CAD file to check the accuracy of the PDF rendering and parsing!
#for example, the CAD software I used generated the following circles for holes:
#CAD hole size:   parsed PDF diameter:      error:
#  .014                .016                +.002
#  .020                .02267              +.00267
#  .025                .026                +.001
#  .029                .03167              +.00267
#  .033                .036                +.003
#  .040                .04267              +.00267
#This was usually ~ .002" - .003" too big compared to the hole as displayed in the CAD software.
#To compensate for PDF rendering errors (either during CAD Print function or PDF parsing logic), adjust the values below as needed.
#units are pixels; for example, a value of 2.4 at 600 dpi = .0004 inch, 2 at 600 dpi = .0033"
use constant
{
    HOLE_ADJUST => -0.004 * 600, #-2.6, #holes seemed to be slightly oversized (by .002" - .004"), so shrink them a little
    RNDPAD_ADJUST => -0.003 * 600, #-2, #-2.4, #round pads seemed to be slightly oversized, so shrink them a little
    SQRPAD_ADJUST => +0.001 * 600, #+.5, #square pads are sometimes too small by .00067, so bump them up a little
    RECTPAD_ADJUST => 0, #(pixels) rectangular pads seem to be okay? (not tested much)
    TRACE_ADJUST => 0, #(pixels) traces seemed to be okay?
    REDUCE_TOLERANCE => .001, #(inches) allow this much variation when reducing circles and rects
};

#Also, my CAD's Print function or the PDF print driver I used was a little off for circles, so define some additional adjustment values here:
#Values are added to X/Y coordinates; units are pixels; for example, a value of 1 at 600 dpi would be ~= .002 inch
use constant
{
    CIRCLE_ADJUST_MINX => 0,
    CIRCLE_ADJUST_MINY => -0.001 * 600, #-1, #circles were a little too high, so nudge them a little lower
    CIRCLE_ADJUST_MAXX => +0.001 * 600, #+1, #circles were a little too far to the left, so nudge them a little to the right
    CIRCLE_ADJUST_MAXY => 0,
    SUBST_CIRCLE_CLIPRECT => FALSE, #generate circle and substitute for clip rects (to compensate for the way some CAD software draws circles)
    WANT_CLIPRECT => TRUE, #FALSE, #AI doesn't need clip rect at all? should be on normally?
    RECT_COMPLETION => FALSE, #TRUE, #fill in 4th side of rect when 3 sides found
};

#allow .012 clearance around pads for solder mask:
#This value effectively adjusts pad sizes in the TOOL_SIZES list above (only for solder mask layers).
use constant SOLDER_MARGIN => +.012; #units are inches

#line join/cap styles:
use constant
{
    CAP_NONE => 0, #butt (none); line is exact length
    CAP_ROUND => 1, #round cap/join; line overhangs by a semi-circle at either end
    CAP_SQUARE => 2, #square cap/join; line overhangs by a half square on either end
    CAP_OVERRIDE => FALSE, #cap style overrides drawing logic
};
    
#number of elements in each shape type:
use constant
{
    RECT_SHAPELEN => 6, #x0, y0, x1, y1, count, "rect" (start, end corners)
    LINE_SHAPELEN => 6, #x0, y0, x1, y1, count, "line" (line seg)
    CURVE_SHAPELEN => 10, #xstart, ystart, x0, y0, x1, y1, xend, yend, count, "curve" (bezier 2 points)
    CIRCLE_SHAPELEN => 5, #x, y, 5, count, "circle" (center + radius)
};
#const my %SHAPELEN =
#Readonly my %SHAPELEN =>
our %SHAPELEN =
(
    rect => RECT_SHAPELEN,
    line => LINE_SHAPELEN,
    curve => CURVE_SHAPELEN,
    circle => CIRCLE_SHAPELEN,
);

#panelization:
#This will repeat the entire body the number of times indicated along the X or Y axes (files grow accordingly).
#Display elements that overhang PCB boundary can be squashed or left as-is (typically text or other silk screen markings).
#Set "overhangs" TRUE to allow overhangs, FALSE to truncate them.
#xpad and ypad allow margins to be added around outer edge of panelized PCB.
use constant PANELIZE => {'x' => 1, 'y' => 1, 'xpad' => 0, 'ypad' => 0, 'overhangs' => TRUE}; #number of times to repeat in X and Y directions

# Set this to 1 if you need TurboCAD support.
#$turboCAD = FALSE; #is this still needed as an option?

#CIRCAD pad generation uses an appropriate aperture, then moves it (stroke) "a little" - we use this to find pads and distinguish them from PCB holes. 
use constant PAD_STROKE => 0.3; #0.0005 * 600; #units are pixels
#convert very short traces to pads or holes:
use constant TRACE_MINLEN => .001; #units are inches
#use constant ALWAYS_XY => TRUE; #FALSE; #force XY even if X or Y doesn't change; NOTE: needs to be TRUE for all pads to show in FlatCAM and ViewPlot
use constant REMOVE_POLARITY => FALSE; #TRUE; #set to remove subtractive (negative) polarity; NOTE: must be FALSE for ground planes

#PDF uses "points", each point = 1/72 inch
#combined with a PDF scale factor of .12, this gives 600 dpi resolution (1/72 * .12 = 600 dpi)
use constant INCHES_PER_POINT => 1/72; #0.0138888889; #multiply point-size by this to get inches

# The precision used when computing a bezier curve. Higher numbers are more precise but slower (and generate larger files).
#$bezierPrecision = 100;
use constant BEZIER_PRECISION => 36; #100; #use const; reduced for faster rendering (mainly used for silk screen and thermal pads)

# Ground planes and silk screen or larger copper rectangles or circles are filled line-by-line using this resolution.
use constant FILL_WIDTH => .01; #fill at most 0.01 inch at a time

# The max number of characters to read into memory
use constant MAX_BYTES => 10 * M; #bumped up to 10 MB, use const

use constant DUP_DRILL1 => TRUE; #FALSE; #kludge: ViewPlot doesn't load drill files that are too small so duplicate first tool

my $runtime = time(); #Time::HiRes::gettimeofday(); #measure my execution time

print STDERR "Loaded config settings from '${\(__FILE__)}'.\n";
1; #last value must be truthful to indicate successful load


#############################################################################################
#junk/experiment:

#use Package::Constants;
#use Exporter qw(import); #https://perldoc.perl.org/Exporter.html

#my $caller = "pdf2gerb::";

#sub cfg
#{
#    my $proto = shift;
#    my $class = ref($proto) || $proto;
#    my $settings =
#    {
#        $WANT_DEBUG => 990, #10; #level of debug wanted; higher == more, lower == less, 0 == none
#    };
#    bless($settings, $class);
#    return $settings;
#}

#use constant HELLO => "hi there2"; #"main::HELLO" => "hi there";
#use constant GOODBYE => 14; #"main::GOODBYE" => 12;

#print STDERR "read cfg file\n";

#our @EXPORT_OK = Package::Constants->list(__PACKAGE__); #https://www.perlmonks.org/?node_id=1072691; NOTE: "_OK" skips short/common names

#print STDERR scalar(@EXPORT_OK) . " consts exported:\n";
#foreach(@EXPORT_OK) { print STDERR "$_\n"; }
#my $val = main::thing("xyz");
#print STDERR "caller gave me $val\n";
#foreach my $arg (@ARGV) { print STDERR "arg $arg\n"; }

Download Details:

Author: swannman
Source Code: https://github.com/swannman/pdf2gerb

License: GPL-3.0 license

#perl 

Bulah  Pfeffer

Bulah Pfeffer

1648873833

A Collection of Flutter and Dart Tips and Tricks

Table of Contents

  • LazyStream in Flutter and Dart
  • Cancelable APIs in Flutter
  • Asset Data in Flutter
  • API Caching in Flutter
  • FutureGroup in Dart
  • Flatten Iterable<bool> in Dart
  • Caching Temp Files in Flutter
  • Custom Lists in Dart
  • Optional Chaining in Dart
  • MapList in Flutter
  • Future<bool> in Flutter
  • Async Bloc Init in Flutter
  • Firebase Auth Errors in Flutter
  • Debug Strings in Flutter
  • Keyboard Appearance in Flutter
  • Get String Data in Dart
  • Stream.startWith in Flutter
  • Optional Functions in Dart
  • AnnotatedRegion in Flutter
  • Unordered Map Equality in Dart
  • Iterable to ListView in Flutter
  • Password Mask in Flutter
  • Fast Object.toString() in Dart
  • Copying Bloc State in Flutter
  • Iterable Subscripts in Dart
  • useState in Flutter Hooks
  • Folding Iterables in Dart
  • Custom Iterables in Dart
  • Class Clusters in Dart
  • Iterable +/- in Dart
  • Periodic Streams in Dart
  • EmptyOnError in Dart
  • Stream<T> Initial Value in Flutter
  • Double.normalize in Dart
  • Hide Sensitive Information in Flutter
  • Iterable.compactMap in Dart
  • useEffect in Flutter Hooks
  • Merging Streams in Dart
  • Isolate Stream in Dart
  • Network Image Retry in Flutter
  • Reusable APIs in Flutter
  • ListTile Shadow in Flutter
  • Transparent AppBar in Flutter
  • Constructors on Abstract Classes in Dart
  • @useResult in Dart
  • @mustCallSuper in Dart
  • Object.hash in Dart
  • Expanded Equally in Flutter
  • Random Iterable Value in Dart
  • Hardcoded Strings in Flutter
  • Manually Scroll in List View in Flutter
  • AsyncSnapshot to Widget in Flutter
  • Breadcrumbs in Flutter
  • Unique Map Values in Dart
  • Smart Quotes/Dashes in Flutter
  • Haptic Feedback in Flutter
  • Localization Delegates in Flutter
  • Extending Functions in Dart
  • Paginated ListView in Flutter
  • Immutable Classes in Dart
  • Card Widget in Flutter
  • List Equality Ignoring Ordering in Dart
  • Shorten GitHub URLs in Dart
  • Time Picker in Flutter
  • Throttled Print in Flutter
  • Map Equality in Dart
  • Unique Maps in Dart
  • Raw Auto Complete in Flutter
  • Title on Object in Dart
  • Compute in Flutter
  • Filter on Map in Dart
  • Type Alias in Dart
  • ValueNotifier in Flutter
  • Object to Integer in Dart
  • Image Opacity in Flutter
  • Covariant in Dart
  • Custom Errors in Streams in Dart
  • Shake Animation in Flutter
  • Throw Enums in Dart
  • Future Error Test in Flutter
  • Generic URL Retrieval in Dart
  • Custom Error Widget in Flutter
  • Handle Multiple Future Errors in Dart
  • Future Error Handling in Dart
  • String to Toast in Flutter
  • Waiting in Dart
  • Loading Dialog in Flutter
  • Compact Map on Map<K,V> in Dart
  • Query Parameters in Dart
  • Multiple Gradients in Container in Flutter
  • Filter on Stream<List<T>> in Dart
  • Generic Route Arguments in Flutter
  • Generic Dialog in Flutter
  • GitHub API in Flutter
  • ChangeNotifier in Flutter
  • Refresh Indicator in Flutter
  • FlatMap in Dart
  • OrientationBuilder in Flutter
  • Linear Gradient in Flutter
  • Bloc Text Editing Controller in Flutter
  • Blurred TabBar in Flutter
  • Play YouTube in Flutter
  • ListView Background in Flutter
  • Integer to Binary in Dart
  • Split String by Length in Dart
  • Image Tint in Flutter
  • SlideTransition in Flutter
  • Expansion Panels and Lists in Flutter
  • Complete CRUD App in Flutter
  • SQLite Storage in Flutter
  • Circular Progress with Percentage in Flutter
  • Opening URLs in Flutter
  • Commodore 64 Screen in Flutter
  • Animated Lists in Flutter
  • CheckboxListTile in Flutter
  • - Operator on String in Dart
  • Dart Progress for Future<T>
  • Move Widget Shadows with Animation
  • Gallery with Blurred Backgrounds in Flutter
  • Custom Path Clippers in Flutter
  • Frost Effect on Images in Flutter
  • Custom Clippers in Flutter
  • Check if Website is Up or Down in Dart
  • Section Titles on ListView in Flutter
  • Circular Progress in Flutter
  • Displaying Scroll Wheels in Flutter
  • Post Messages to Slack with Dart
  • Unwrap List<T?>? in Dart
  • Avoiding UI Jitters When Switching Widgets in Flutter
  • Detect Redirects in Dart
  • Proportional Constraints in Flutter
  • Displaying Cupertino Action Sheets in Flutter
  • Rotating List<T> in Dart
  • Displaying SnackBars in Flutter
  • Custom Tab Bar Using ToggleButtons in Flutter
  • Hashable Mixins in Dart
  • Flutter Tips and Tricks in Terminal
  • Searching List<List<T>> in Dart
  • Cloning Objects in Dart
  • Color Filters in Flutter
  • Flattening Lists in Dart
  • Managing Duplicates in List<T> in Dart
  • FlatMap and CompactMap in Dart
  • Equality of List<T> in Dart
  • Constants in Dart
  • Displaying Scrollable Bottom Sheets in Flutter
  • YouTube Ad Remover in Dart
  • Fade Between Widgets in Flutter
  • Sort Descriptors in Dart
  • User Sortable Columns and Tables in Flutter
  • Content-Length of List<Uri> in Dart
  • Recursive Dot Notation on Maps in Dart
  • Allow User Selection of Text in Flutter
  • Placing Constraints on Widgets in Flutter
  • Animating Position Changes in Flutter
  • Transitioning Between Widgets in Flutter
  • Doubly Linked Lists in Dart
  • Reordering Items Inside List Views in Flutter
  • Custom Stream Transformers in Dart
  • Expanding Stream Elements in Dart
  • Consume Streams for a Duration in Dart
  • Shortening URLs in Dart
  • LimitedBox Widget as ListView Items in Flutter
  • Generically Convert Anything to Int in Dart
  • Validating URL Certificates in Dart
  • Displaying Popup Menus in Flutter
  • Implementing Drag and Drop in Flutter
  • Dismissing List Items in Flutter
  • Animating Widgets with Ease in Flutter
  • Displaying Tool Tips in Flutter
  • Displaying Assorted Widgets Inside TableView in Flutter
  • Page Indicator with Page View in Flutter
  • Animating and Moving a Floating Action Button in Flutter
  • Fading Network Image Widget in Flutter
  • Transparent Alert Dialogs in Flutter
  • Network Image Size in Dart
  • Animated Icons in Flutter
  • Custom Scroll Views in Flutter
  • Parallax App Bar in Flutter
  • JSON HTTP Requests in Dart
  • URL Timeouts in Dart
  • Detecting URL File Types in Dart
  • Paginated Lists in Dart
  • Requesting DELETE on APIs in Dart
  • Animated Containers in Flutter
  • Hiding Widgets in Flutter
  • Simple Opacity Animation in Flutter
  • Vignette Widget in Flutter
  • Drop Down Button Configuration and Usage in Flutter
  • Expandable List Items in Flutter
  • Infinite Scrolling in Flutter
  • Infinite Arrays in Dart
  • Custom Color Picker Component in Flutter
  • Displaying and Reacting to Switches in Flutter
  • Displaying Bottom Bars in Flutter
  • Displaying Buttons on AppBar in Flutter
  • Displaying Bottom Sheets in Flutter
  • Converting Enums to Radio Buttons in Flutter
  • Check Existence of Websites in Flutter
  • Images inside AlertDialog in Flutter
  • Returning Values from AlertDialog in Flutter
  • Simple Grid View in Flutter
  • Rendering Bullet Points in Flutter
  • Retrying Futures in Flutter
  • Containers as ClipOvals in Flutter
  • Rich Texts in Flutter
  • Wrapping Widgets in Flutter
  • Sweep Gradients in Flutter
  • Stream and StreamBuilder in Flutter
  • Blur Effect in Flutter
  • Convert Enums to Strings in Dart
  • Replacing Text in TextField in Flutter
  • Aspect Ratio in Flutter
  • Zoom and Pan in Flutter
  • Resizing Images in Flutter to Fit Screen Height
  • Validating URLs in Flutter
  • FrameBuilder for Network Images in Flutter
  • Adding Shadow to Icons in Flutter
  • Calculating Median of Lists in Dart
  • Generic Functions with Reduce in Dart
  • Passing Back Data From a Screen to the Previous One in Flutter
  • Flinging an Animation in Flutter
  • Fade Animations in Flutter
  • Throttling User Input in Flutter
  • Censoring TextFields in Flutter
  • Customizing TextButton in Flutter
  • Multiline TextFields in Flutter
  • Filtering TextField Input in Flutter
  • Focusing Manually on TextFields in Flutter
  • Data Streams Over HTTP/HTTPs in Dart
  • Catching Nonexistent Accessors or Methods in Dart
  • Using Expando in Dart
  • Implementing Custom Maps in Dart
  • Dynamically Calling Functions in Dart
  • Factory Constructors in Dart
  • Calculating the Sum of List Items in Dart
  • Removing Duplicate Strings in Lists in Dart (Case-Insensitive)
  • Implementing Range in Dart
  • Converting Lists to Maps in Dart
  • Implementing Hashable in Dart
  • Random Name Generator in Dart
  • Capturing Stack Traces in Dart Exceptions
  • Removing Duplicates from Lists in Dart
  • Optional Spread Operator in Dart
  • Calling Optional Functions in Dart
  • Odd-Even Sort in Dart
  • Implementing Zip and Tuples in Dart
  • Swapping Values in Lists with XOR in Dart
  • Waiting for Multiple Futures in Dart
  • Using Queues as Stacks in Dart
  • Custom Iterators in Dart
  • Iterables as Ranges + Transform in Dart
  • Errors vs Exceptions in Dart
  • Custom Annotations in Dart
  • Classes as Enums in Dart
  • Spread Operator in Collection Literals in Dart
  • StreamBuilder and StreamController in Dart
  • Almost Equal in Dart
  • Enum Associated Values in Dart
  • Implementing Comparable in Dart
  • Implementing Custom Integer Types in Dart
  • Custom Subscripts in Dart
  • Dart List Enumeration with Index
  • Applying Mixins to Other Mixins in Dart
  • Parameter Types in Dart
  • Custom Exceptions in Dart
  • rethrowing Exceptions in Dart
  • mixins and JSON Parsing in Dart
  • mixins vs abstract classes in Dart
  • Drawing Shapes in Flutter with LayoutBuilder, CustomPaint and CustomPainter
  • Generic Type Aliases in Dart
  • Callable Classes in Dart
  • Synchronous Generators in Dart
  • Implicit Interfaces in Dart
  • const Constructors in Dart
  • async-await Over Raw Futures in Dart
  • Initializer List and Default Values as Convenience Intializers in Dart
  • Extract Elements of Certain Type from Lists in Dart
  • Type Promotion in Dart
  • Extract Minimum and Maximum Values in List<num> in Dart
  • Functions as First Class Citizens in Dart

 

LazyStream in Flutter and Dart



import 'dart:developer' as devtools show log;
import 'dart:typed_data' show Uint8List;
import 'package:flutter/services.dart' show NetworkAssetBundle, rootBundle;
import 'package:async/async.dart' show LazyStream;

extension LocalFileData on String {
  Future<Uint8List> localFileData() => rootBundle.load(this).then(
        (byteData) => byteData.buffer.asUint8List(),
      );
}

extension Log on Object {
  void log() => devtools.log(toString());
}

void testIt() async {
  final stream = LazyStream(
    () async {
      final allData = await calculateAllData();
      return getImagesData(allData);
    },
  );

  await for (final data in stream) {
    'Got data, length = ${data.length}'.log();
  }
}

Stream<Uint8List> getImagesData(
  List<Future<Uint8List>> allData,
) async* {
  for (final data in allData) {
    yield await data;
  }
}

Future<List<Future<Uint8List>>> calculateAllData() async {
  final futures = Iterable.generate(
    3,
    (i) => 'images/image_list${i + 1}.txt'
        .localFileData()
        .then((data) => String.fromCharCodes(data)),
  );
  final result = Future.wait(futures);
  final lineSplitter = const LineSplitter();
  List<Future<Uint8List>> allData = [];
  for (final string in await result) {
    final urls = lineSplitter.convert(string);
    for (final url in urls) {
      allData.add(
        NetworkAssetBundle(Uri.parse(url))
            .load(url)
            .then((byteData) => byteData.buffer.asUint8List()),
      );
    }
  }
  return allData;
}

Cancelable APIs in Flutter

import 'dart:developer' as devtools show log;
import 'dart:typed_data' show Uint8List;
import 'package:flutter/services.dart' show NetworkAssetBundle, rootBundle;
import 'package:async/async.dart' show CancelableOperation;

extension Log on Object {
  void log() => devtools.log(toString());
}

extension LocalFileData on String {
  Future<Uint8List> localFileData() => rootBundle.load(this).then(
        (byteData) => byteData.buffer.asUint8List(),
      );
}

CancelableOperation<Uint8List> getImageOperation(String url) =>
    CancelableOperation.fromFuture(
      NetworkAssetBundle(Uri.parse(url))
          .load(url)
          .then((byteData) => byteData.buffer.asUint8List()),
      onCancel: () => 'images/template.png'.localFileData(),
    );

void testIt() async {
  final operation = getImageOperation('http://127.0.0.1:5500/images/1.png');
  final cancelledValue = await operation.cancel();
  final result = await operation.valueOrCancellation(cancelledValue);
  result?.log();
}

Asset Data in Flutter


import 'dart:typed_data' show Uint8List;
import 'package:flutter/services.dart' show rootBundle;
import 'dart:developer' as devtools show log;

extension Log on Object {
  void log() => devtools.log(toString());
}

extension LocalFileData on String {
  Future<Uint8List> localFileData() => rootBundle.load(this).then(
        (byteData) => byteData.buffer.asUint8List(),
      );
}

void testIt() async {
  (await 'images/template.png'.localFileData()).log();
}

API Caching in Flutter


import 'dart:typed_data' show Uint8List;
import 'package:flutter/services.dart' show NetworkAssetBundle;
import 'dart:developer' as devtools show log;
import 'package:async/async.dart' show AsyncMemoizer;

extension Log on Object {
  void log() => devtools.log(toString());
}

@immutable
class GetImageApi {
  final String url;
  final _fetch = AsyncMemoizer<Uint8List>();

  GetImageApi({required this.url});
  Future<Uint8List> fetch() => _fetch.runOnce(
        () => NetworkAssetBundle(Uri.parse(url))
            .load(url)
            .then((byteData) => byteData.buffer.asUint8List()),
      );
}

void testIt() async {
  final api = GetImageApi(url: 'http://127.0.0.1:5500/images/1.png');
  (await api.fetch()).log(); // fetched
  (await api.fetch()).log(); // cached
}

FutureGroup in Dart



mixin FutureConvertible<T> {
  Future<T> toFuture();
}

@immutable
class LoginApi with FutureConvertible<bool> {
  @override
  Future<bool> toFuture() => Future.delayed(
        const Duration(seconds: 1),
        () => true,
      );
}

@immutable
class SignUpApi with FutureConvertible<bool> {
  @override
  Future<bool> toFuture() => Future.delayed(
        const Duration(seconds: 1),
        () => true,
      );
}

extension Flatten on Iterable<bool> {
  bool flatten() => fold(
        true,
        (lhs, rhs) => lhs && rhs,
      );
}

extension Log on Object {
  void log() => devtools.log(toString());
}

Future<bool> startup({
  required bool shouldLogin,
  required bool shouldSignUp,
}) {
  final group = FutureGroup<bool>();
  if (shouldLogin) {
    group.add(LoginApi().toFuture());
  }
  if (shouldSignUp) {
    group.add(SignUpApi().toFuture());
  }
  group.close();
  return group.future.then((bools) => bools.flatten());
}

void testIt() async {
  final success = await startup(
    shouldLogin: true,
    shouldSignUp: false,
  );
  success.log();
}

Flatten Iterable<bool> in Dart


extension Flatten on Iterable<bool> {
  bool flatten() => fold(
        true,
        (lhs, rhs) => lhs && rhs,
      );
}

void testIt() {
  assert([true, false, true].flatten() == false);
  assert([true, true, true].flatten() == true);
  assert([false, false, false].flatten() == false);
  assert([true].flatten() == true);
  assert([false].flatten() == false);
}

Caching Temp Files in Flutter



@immutable
class NetworkImageAsset {
  final String localPath;
  final String url;
  NetworkImageAsset({required int index})
      : localPath = Directory.systemTemp.path + '/$index.png',
        url = 'http://127.0.0.1:5500/images/$index}.png';

  Future<bool> downloadAndSave() => NetworkAssetBundle(Uri.parse(url))
      .load(url)
      .then((byteData) => byteData.buffer.asUint8List())
      .then((data) => File(localPath).writeAsBytes(data).then((_) => true))
      .catchError((_) => false);
}

void testIt() async {
  await Future.forEach(
    Iterable.generate(
      3,
      (i) => NetworkImageAsset(index: i + 1),
    ),
    (NetworkImageAsset asset) => asset.downloadAndSave(),
  );
}

Custom Lists in Dart



import 'dart:developer' as devtools show log;
import 'dart:collection' show ListBase;

class LowercaseList extends ListBase<String> {
  final List<String> _list = [];

  @override
  int get length => _list.length;
  @override
  set length(int newLength) => _list.length = newLength;

  @override
  String operator [](int index) => _list[index].toUpperCase();

  @override
  void operator []=(int index, value) => _list[index] = value;

  @override
  void addAll(Iterable<String> iterable) => _list.addAll(iterable);

  @override
  void add(String element) => _list.add(element);
}

extension Log on Object {
  void log() => devtools.log(toString());
}

void testIt() {
  final myList = LowercaseList();
  myList.addAll(['foo', 'bar', 'baz']);
  myList[0].log(); // FOO
  myList[1].log(); // BAR
  for (final item in myList) {
    item.log(); // FOO, BAR, BAZ
  }
}

Optional Chaining in Dart



@immutable
class Address {
  final String? firstLine;
  final String? secondLine;
  const Address(this.firstLine, this.secondLine);
}

@immutable
class Person {
  final Person? father;
  final Address? address;
  const Person(this.father, this.address);
}

extension GetFathersFirstAddressLine on Person {
  String? get firstAddressLineOfFather => father?.address?.firstLine;
}

MapList in Flutter



extension MapToList<T> on Iterable<T> {
  List<E> mapList<E>(E Function(T) toElement) => 
    map(toElement).toList();
}

Future<bool> in Flutter



Future<bool> uploadImage({
  required File file,
  required String userId,
}) =>
    FirebaseStorage.instance
        .ref(userId)
        .child(const Uuid().v4())
        .putFile(file)
        .then((_) => true)
        .catchError((_) => false);

Async Bloc Init in Flutter



class App extends StatelessWidget {
  const App({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return BlocProvider<AppBloc>(
      create: (context) => AppBloc()..add(const AppEventInitialize()),
      child: MaterialApp(
        title: 'Photo Library',
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        debugShowCheckedModeBanner: false,
        home: BlocConsumer<AppBloc, AppState>(
          listener: (context, state) {
            // handle loading
            if (state.isLoading) {
              LoadingScreen().show(
                context: context,
                text: 'Loading...',
              );
            } else {
              LoadingScreen().hide();
            }
            
            ... rest of your code goes here

Firebase Auth Errors in Flutter



const authErrorMapping = {
  'user-not-found': AuthErrorUserNotFound(),
  'project-not-found': AuthErrorProjectNotFound(),
};

@immutable
abstract class AuthError {
  factory AuthError.from(FirebaseAuthException exception) =>
      authErrorMapping[exception.code.toLowerCase().trim()] ??
      const AuthErrorUnknown();
}

@immutable
class AuthErrorUnknown implements AuthError {
  const AuthErrorUnknown();
}

@immutable
class AuthErrorUserNotFound implements AuthError {
  const AuthErrorUserNotFound();
}

@immutable
class AuthErrorProjectNotFound implements AuthError {
  const AuthErrorProjectNotFound();
}

Debug Strings in Flutter


extension IfDebugging on String {
  String? get ifDebugging => kDebugMode ? this : null;
}

class LoginView extends HookWidget {
  const LoginView({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final emailController = useTextEditingController(
      text: 'foo@bar.com'.ifDebugging,
    );
    final passwordController = useTextEditingController(
      text: 'foobarbaz'.ifDebugging,
    );
    
    // rest of your code would be here ...

Keyboard Appearance in Flutter


class LoginView extends HookWidget {
  const LoginView({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Log in'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(8.0),
        child: Column(
          children: const [
            TextField(
              keyboardType: TextInputType.emailAddress,
              keyboardAppearance: Brightness.dark,
            ),
            TextField(
              obscureText: true,
              obscuringCharacter: '◉',
            ),
          ],
        ),
      ),
    );
  }
}

Get String Data in Dart


extension ToList on String {
  Uint8List toUint8List() => Uint8List.fromList(codeUnits);
}

final text1Data = 'Foo'.toUint8List();
final text2Data = 'Bar'.toUint8List();

Stream.startWith in Flutter


import 'package:async/async.dart' show StreamGroup;
import 'dart:developer' as devtools show log;

extension Log on Object {
  void log() => devtools.log(toString());
}

extension StartWith<T> on Stream<T> {
  Stream<T> startWith(T value) => StreamGroup.merge([
        this,
        Stream<T>.value(value),
      ]);
}

void testIt() {
  Stream.periodic(const Duration(seconds: 1), (i) => i + 1)
      .startWith(0)
      .take(4)
      .forEach((element) {
    element.log();
  }); // 0, 1, 2, 3
}

Optional Functions in Dart



typedef AppBlocRandomUrlPicker = String Function(Iterable<String> allUrls);

extension RandomElement<T> on Iterable<T> {
  T getRandomElement() => elementAt(
        math.Random().nextInt(length),
      );
}

class AppBloc extends Bloc<AppEvent, AppState> {
  String _pickRandomUrl(Iterable<String> allUrls) => allUrls.getRandomElement();

  AppBloc({
    required Iterable<String> urls,
    AppBlocRandomUrlPicker? urlPicker,
  }) : super(const AppState.empty()) {
    on<LoadNextUrlEvent>(
      (event, emit) {
        emit(
          const AppState(
            isLoading: true,
            data: null,
          ),
        );
        // pick a random URL to load
        final url = (urlPicker ?? _pickRandomUrl)(urls);
        HttpClient().getUrl(Uri.parse(url)); // continue here...
      },
    );
  }
}

AnnotatedRegion in Flutter



class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: AnnotatedRegion<SystemUiOverlayStyle>(
        value: SystemUiOverlayStyle.dark,
        child: Column(
          mainAxisSize: MainAxisSize.max,
          children: [
            Expanded(child: Container(color: Colors.blue)),
            Expanded(child: Container(color: Colors.yellow)),
          ],
        ),
      ),
    );
  }
}

Unordered Map Equality in Dart



import 'package:collection/collection.dart';
import 'dart:developer' as devtools show log;

extension Log on Object {
  void log() => devtools.log(toString());
}

extension UnorderedEquality<K, V> on Map<K, V> {
  bool isEqualTo(Map<K, V> other) =>
      const DeepCollectionEquality.unordered().equals(this, other);
}

void testIt() {
  final dict1 = {
    'name': 'foo',
    'age': 20,
    'values': ['foo', 'bar'],
  };
  final dict2 = {
    'age': 20,
    'name': 'foo',
    'values': ['bar', 'foo'],
  };
  dict1.isEqualTo(dict2).log(); // true
}

Iterable to ListView in Flutter



extension ToListView<T> on Iterable<T> {
  Widget toListView() => IterableListView(
        iterable: this,
      );
}

class IterableListView<T> extends StatelessWidget {
  final Iterable<T> iterable;
  const IterableListView({
    Key? key,
    required this.iterable,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return ListView.builder(
      itemCount: iterable.length,
      itemBuilder: (context, index) {
        return ListTile(
          title: Text(
            iterable.elementAt(index).toString(),
          ),
        );
      },
    );
  }
}

@immutable
class Person {
  final String name;
  final int age;
  const Person({required this.name, required this.age});
  @override
  String toString() => '$name, $age years old';
}

const persons = [
  Person(name: 'Foo', age: 20),
  Person(name: 'Bar', age: 30),
  Person(name: 'Baz', age: 40),
];

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Home Page'),
      ),
      body: persons.toListView(),
    );
  }
}

Password Mask in Flutter



class PasswordTextField extends StatelessWidget {
  const PasswordTextField({
    Key? key,
    required this.passwordController,
  }) : super(key: key);

  final TextEditingController passwordController;

  @override
  Widget build(BuildContext context) {
    return TextField(
      controller: passwordController,
      obscureText: true,
      obscuringCharacter: '◉',
      decoration: const InputDecoration(
        hintText: 'Enter your password here...',
      ),
    );
  }
}

Fast Object.toString() in Dart



@immutable
class AppState {
  final bool isLoading;
  final Object? loginError;
  final String? loginHandle;
  final Iterable<String>? fetchedNotes;

  @override
  String toString() => {
        'isLoading': isLoading,
        'loginError': loginError,
        'loginHandle': loginHandle,
        'fetchedNotes': fetchedNotes
      }.toString();

  const AppState({
    required this.isLoading,
    required this.loginError,
    required this.loginHandle,
    required this.fetchedNotes,
  });
}

Copying Bloc State in Flutter



@immutable
class AppState {
  final bool isLoading;
  final LoginHandle? loginHandle;
  final Iterable<Note>? fetchedNotes;

  const AppState.empty()
      : isLoading = false,
        loginHandle = null,
        fetchedNotes = null;

  const AppState({
    required this.isLoading,
    required this.loginHandle,
    required this.fetchedNotes,
  });

  AppState copiedWith({
    bool? isLoading,
    LoginHandle? loginHandle,
    Iterable<Note>? fetchedNotes,
  }) =>
      AppState(
        isLoading: isLoading ?? this.isLoading,
        loginHandle: loginHandle ?? this.loginHandle,
        fetchedNotes: fetchedNotes ?? this.fetchedNotes,
      );
}

Iterable Subscripts in Dart

// Free Flutter Course 💙 https://linktr.ee/vandadnp
// Want to support my work 🤝? https://buymeacoffee.com/vandad

import 'dart:developer' as devtools show log;

extension Log on Object? {
  void log() => devtools.log(toString());
}

extension Subscript<T> on Iterable<T> {
  T? operator [](int index) => length > index ? elementAt(index) : null;
}

void testIt() {
  Iterable.generate(10, (i) => i + 1)[0].log(); // 1
  Iterable.generate(1, (i) => i)[2].log(); // null
  Iterable.generate(10, (i) => i + 1)[9].log(); // 10
  Iterable.generate(0, (i) => i)[0].log(); // null
}

useState in Flutter Hooks



import 'package:flutter_hooks/flutter_hooks.dart';
import 'dart:math' show min;

@immutable
class VirtualTab {
  final Icon icon;
  final String text;

  const VirtualTab({
    required this.icon,
    required this.text,
  });
}

const tabs = [
  VirtualTab(
    icon: Icon(Icons.picture_as_pdf),
    text: 'All PDF files',
  ),
  VirtualTab(
    icon: Icon(Icons.ac_unit_outlined),
    text: 'Data page',
  ),
  VirtualTab(
    icon: Icon(Icons.person),
    text: 'Profile page',
  ),
];

class HomePage extends HookWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final tabCount = useState(1);
    return DefaultTabController(
      length: tabCount.value,
      initialIndex: tabCount.value - 1,
      child: Scaffold(
        appBar: AppBar(
          bottom: TabBar(
            tabs: tabs
                .take(tabCount.value)
                .map((tab) => Tab(icon: tab.icon))
                .toList(),
          ),
        ),
        body: CustomTabBarView(tabCount: tabCount),
      ),
    );
  }
}

class CustomTabBarView extends StatelessWidget {
  const CustomTabBarView({
    Key? key,
    required this.tabCount,
  }) : super(key: key);

  final ValueNotifier<int> tabCount;

  @override
  Widget build(BuildContext context) {
    return TabBarView(
      children: tabs
          .take(tabCount.value)
          .map(
            (tab) => Padding(
              padding: const EdgeInsets.all(8.0),
              child: Column(
                children: [
                  Text(tab.text),
                  TextButton(
                    onPressed: () {
                      final newLength = min(
                        tabs.length,
                        tabCount.value + 1,
                      );
                      tabCount.value = newLength;
                    },
                    child: const Text('Create next tab'),
                  )
                ],
              ),
            ),
          )
          .toList(),
    );
  }
}

 

Folding Iterables in Dart



import 'dart:developer' as devtools show log;

extension Log on Object {
  void log() => devtools.log(toString());
}

void testIt() {
  final values = ['foo', 'bar', 'baz', '1.0'];

  values.fold<int>(0, (pe, e) => pe + e.length); // 12

  values.fold<String>('', (pe, e) => '$pe$e'); // foobarbaz1.0

  values.fold<Map<String, int>>(
    {},
    (pe, e) => pe..addAll(<String, int>{e: e.length}),
  ).log(); // {foo: 3, bar: 3, baz: 3, 1.0: 3}

  values.fold<double>(
    0.0,
    (pe, e) => pe + (double.tryParse(e) ?? 0.0),
  ); // 1.0
}

Custom Iterables in Dart



class Address with IterableMixin {
  final String line1;
  final String line2;
  final String postCode;

  Address({
    required this.line1,
    required this.line2,
    required this.postCode,
  });

  @override
  Iterator<String> get iterator => [line1, line2, postCode].iterator;
}

void testIt() {
  final address = Address(
    line1: 'Foo bar avenue, #10',
    line2: 'Baz street',
    postCode: '123456',
  );
  for (final line in address) {
    devtools.log(line);
  }
}

Class Clusters in Dart



enum AnimalType { dog, cat }

@immutable
abstract class Animal {
  const Animal();
  factory Animal.fromType(AnimalType type) {
    switch (type) {
      case AnimalType.dog:
        return const Dog();
      case AnimalType.cat:
        return const Cat();
    }
  }
  void makeNoise();
}

@immutable
class Dog extends Animal {
  const Dog();
  @override
  void makeNoise() => 'Woof'.log();
}

@immutable
class Cat extends Animal {
  const Cat();
  @override
  void makeNoise() => 'Meow'.log();
}

void testIt() {
  final cat = Animal.fromType(AnimalType.cat);
  cat.makeNoise();
  final dog = Animal.fromType(AnimalType.dog);
  dog.makeNoise();
}

Iterable +/- in Dart



extension AddRemoveItems<T> on Iterable<T> {
  Iterable<T> operator +(T other) => followedBy([other]);
  Iterable<T> operator -(T other) => where((element) => element != other);
}

void testIt() {
  final values = ['foo', 'bar']
    .map((e) => e.toUpperCase()) + 'BAZ';
  values.log(); // (FOO, BAR, BAZ)
  (values - 'BAZ').log(); // (FOO, BAR)
}

Periodic Streams in Dart



import 'dart:io';
import 'package:flutter/material.dart';
import 'dart:convert';
import 'dart:developer' as devtools show log;

extension Log on Object {
  void log() => devtools.log(toString());
}

@immutable
class Person {
  final String name;
  final int age;

  const Person({
    required this.name,
    required this.age,
  });

  Person.fromJson(Map<String, dynamic> json)
      : name = json["name"] as String,
        age = json["age"] as int;

  @override
  String toString() => 'Person ($name, $age years old)';
}

mixin ListOfThingsAPI<T> {
  Future<Iterable<T>> get(String url) => HttpClient()
      .getUrl(Uri.parse(url))
      .then((req) => req.close())
      .then((resp) => resp.transform(utf8.decoder).join())
      .then((str) => json.decode(str) as List<dynamic>)
      .then((list) => list.cast());
}

class GetPeople with ListOfThingsAPI<Map<String, dynamic>> {
  Future<Iterable<Person>> getPeople(url) => get(url).then(
        (jsons) => jsons.map(
          (json) => Person.fromJson(json),
        ),
      );
}

Stream<dynamic> every(Duration duration) => Stream.periodic(duration);

extension IntToDuration on int {
  Duration get seconds => Duration(seconds: this);
}

void testIt() async {
  await for (final people in every(3.seconds).asyncExpand(
    (_) => GetPeople()
        .getPeople('http://127.0.0.1:5500/apis/people1.json')
        .asStream(),
  )) {
    people.log();
  }
}

/* people1.json
[
    {
        "name": "Foo 1",
        "age": 20
    },
    {
        "name": "Bar 1",
        "age": 30
    }
]
*/

EmptyOnError in Dart



import 'dart:io';
import 'package:flutter/material.dart';
import 'dart:convert';
import 'dart:developer' as devtools show log;

extension Log on Object {
  void log() => devtools.log(toString());
}

@immutable
class Person {
  final String name;
  final int age;

  const Person({
    required this.name,
    required this.age,
  });

  Person.fromJson(Map<String, dynamic> json)
      : name = json["name"] as String,
        age = json["age"] as int;

  @override
  String toString() => 'Person ($name, $age years old)';
}

const people1Url = 'http://127.0.0.1:5500/apis/people11.json';
const people2Url = 'http://127.0.0.1:5500/apis/people2.json';

extension EmptyOnError<E> on Future<List<Iterable<E>>> {
  Future<List<Iterable<E>>> emptyOnError() => catchError(
        (_, __) => List<Iterable<E>>.empty(),
      );
}

Future<Iterable<Person>> parseJson(String url) => HttpClient()
    .getUrl(Uri.parse(url))
    .then((req) => req.close())
    .then((resp) => resp.transform(utf8.decoder).join())
    .then((str) => json.decode(str) as List<dynamic>)
    .then((json) => json.map((e) => Person.fromJson(e)));

void testIt() async {
  final persons = await Future.wait([
    parseJson(people1Url),
    parseJson(people2Url),
  ]).emptyOnError();
  persons.log();
}

Stream<T> Initial Value in Flutter



import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter_hooks/flutter_hooks.dart';

void main() {
  runApp(
    MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      debugShowCheckedModeBanner: false,
      home: const HomePage(),
    ),
  );
}

const url = 'https://bit.ly/3x7J5Qt';

class HomePage extends HookWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    late final StreamController<double> controller;
    controller = useStreamController<double>(onListen: () {
      controller.sink.add(0.0);
    });

    return Scaffold(
      appBar: AppBar(
        title: const Text('Home page'),
      ),
      body: StreamBuilder<double>(
          stream: controller.stream,
          builder: (context, snapshot) {
            if (!snapshot.hasData) {
              return const CircularProgressIndicator();
            } else {
              final rotation = snapshot.data ?? 0.0;
              return GestureDetector(
                onTap: () {
                  controller.sink.add(rotation + 10.0);
                },
                child: RotationTransition(
                  turns: AlwaysStoppedAnimation(rotation / 360.0),
                  child: Center(
                    child: Image.network(url),
                  ),
                ),
              );
            }
          }),
    );
  }
}

Double.normalize in Dart



import 'dart:developer' as devtools show log;

extension Normalize on double {
  double normalized(
    double selfRangeMin,
    double selfRangeMax, [
    double normalizedRangeMin = 0.0,
    double normalizedRangeMax = 1.0,
  ]) =>
      (normalizedRangeMax - normalizedRangeMin) *
          ((this - selfRangeMin) / (selfRangeMax - selfRangeMin)) +
      normalizedRangeMin;
}

extension Log on Object {
  void log() => devtools.log(toString());
}

void testIt() async {
  2.0.normalized(0, 2.0).log(); // 1.0
  4.0.normalized(0, 8.0).log(); // 0.5
  5.0.normalized(4.0, 6.0, 10.0, 20.0).log(); // 15
}

Hide Sensitive Information in Flutter

 



import 'package:flutter/material.dart';
import 'package:flutter_hooks/flutter_hooks.dart';

void main() {
  runApp(
    MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      debugShowCheckedModeBanner: false,
      home: const HomePage(),
    ),
  );
}

class HomePage extends HookWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final state = useAppLifecycleState();
    return Scaffold(
      appBar: AppBar(
        title: const Text('Home Page'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(8.0),
        child: Opacity(
          opacity: state == AppLifecycleState.resumed ? 1.0 : 0.0,
          child: Container(
            decoration: BoxDecoration(
              boxShadow: [
                BoxShadow(
                  blurRadius: 10,
                  color: Colors.black.withAlpha(100),
                  spreadRadius: 10,
                ),
              ],
            ),
            child: Image.asset('assets/card.png'),
          ),
        ),
      ),
    );
  }
}

Iterable.compactMap in Dart



import 'dart:developer' as devtools show log;

extension Log on Object {
  void log() => devtools.log(toString());
}

extension CompactMap<T> on Iterable<T?> {
  Iterable<T> compactMap<E>([
    E? Function(T?)? transform,
  ]) =>
      map(transform ?? (e) => e).where((e) => e != null).cast();
}

const list = ['Hello', null, 'World'];

void testIt() {
  list.log(); // [Hello, null, World]
  list.compactMap().log(); // [Hello, World]
  list.compactMap((e) => e?.toUpperCase()).log(); // [HELLO, WORLD]
}

useEffect in Flutter Hooks



import 'package:flutter/material.dart';
import 'package:flutter_hooks/flutter_hooks.dart';

void main() {
  runApp(
    MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      debugShowCheckedModeBanner: false,
      home: const HomePage(),
    ),
  );
}

class HomePage extends HookWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final controller = useTextEditingController();
    final text = useState('');
    useEffect(
      () {
        void listener() {
          text.value = controller.text;
        }

        controller.addListener(listener);
        return () => controller.removeListener(listener);
      },
      [controller],
    );
    return Scaffold(
      body: Column(
        children: [
          TextField(
            controller: controller,
          ),
          Text('You typed ${text.value}')
        ],
      ),
    );
  }
}

Merging Streams in Dart



import 'package:async/async.dart' show StreamGroup;
import 'dart:developer' as devtools show log;

extension Log on Object {
  void log() => devtools.log(toString());
}

void testIt() async {
  final streams = Iterable.generate(
    3,
    (i) => Stream.periodic(
      const Duration(seconds: 1),
      (_) => 'Stream $i: ${DateTime.now().toIso8601String()}',
    ).take(i + 1),
  );
  await for (final now in StreamGroup.merge(streams)) {
    now.log();
  }
}

Isolate Stream in Dart



Stream<String> getMessages() {
  final rp = ReceivePort();
  return Isolate.spawn(_getMessages, rp.sendPort)
      .asStream()
      .asyncExpand((_) => rp)
      .takeWhile((element) => element is String)
      .cast();
}

void _getMessages(SendPort sp) async {
  await for (final now in Stream.periodic(
    const Duration(seconds: 1),
    (_) => DateTime.now().toIso8601String(),
  ).take(10)) {
    sp.send(now);
  }
  Isolate.exit(sp);
}

void testIt() async {
  await for (final msg in getMessages()) {
    msg.log();
  }
}

Network Image Retry in Flutter



@immutable
class RetryStrategy {
  final bool shouldRetry;
  final Duration waitBeforeRetry;
  const RetryStrategy({
    required this.shouldRetry,
    required this.waitBeforeRetry,
  });
}

typedef Retrier = RetryStrategy Function(String url, Object error);

class NetworkImageWithRetry extends StatelessWidget {
  final Widget loadingWidget;
  final Widget errorWidget;
  final String url;
  final Retrier retrier;

  final _controller = StreamController<Uint8List>.broadcast();

  NetworkImageWithRetry({
    Key? key,
    required this.url,
    required this.retrier,
    required this.loadingWidget,
    required this.errorWidget,
  }) : super(key: key);

  void getData() async {
    while (true == true) {
      try {
        final networkAsset = NetworkAssetBundle(Uri.parse(url));
        final loaded = await networkAsset.load(url);
        final bytes = loaded.buffer.asUint8List();
        _controller.sink.add(bytes);
        break;
      } catch (e) {
        final strategy = retrier(url, e);
        if (strategy.shouldRetry) {
          await Future.delayed(strategy.waitBeforeRetry);
        } else {
          _controller.sink.addError(e);
          break;
        }
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    getData();
    return StreamBuilder(
      stream: _controller.stream,
      builder: (context, AsyncSnapshot<Uint8List> snapshot) {
        if (snapshot.hasError) {
          return errorWidget;
        } else {
          final data = snapshot.data;
          if (snapshot.hasData && data != null) {
            return Image.memory(data);
          } else {
            return loadingWidget;
          }
        }
      },
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Image Retry'),
      ),
      body: NetworkImageWithRetry(
        url: 'https://bit.ly/3qYOtDm',
        errorWidget: const Text('Got an error!'),
        loadingWidget: const Text('Loading...'),
        retrier: (url, error) {
          return RetryStrategy(
            shouldRetry: error is! FlutterError,
            waitBeforeRetry: const Duration(seconds: 1),
          );
        },
      ),
    );
  }
}

Reusable APIs in Flutter

import 'dart:io';
import 'package:flutter/material.dart';
import 'dart:developer' as devtools show log;
import 'dart:convert' show utf8;
import 'package:meta/meta.dart' show useResult;

extension Log on Object {
  void log() => devtools.log(toString());
}

extension GetOnUri on Object {
  Future<HttpClientResponse> getUrl(
    String url,
  ) =>
      HttpClient()
          .getUrl(
            Uri.parse(
              url,
            ),
          )
          .then((req) => req.close());
}

mixin CanMakeGetCall {
  String get url;
  @useResult
  Future<String> getString() => getUrl(url).then(
        (response) => response
            .transform(
              utf8.decoder,
            )
            .join(),
      );
}

@immutable
class GetPeople with CanMakeGetCall {
  const GetPeople();
  @override
  String get url => 'http://127.0.0.1:5500/apis/people.json';
}

void testIt() async {
  final people = await const GetPeople().getString();
  devtools.log(people);
}

ListTile Shadow in Flutter



enum Currency { dollars }

extension Title on Currency {
  String get title {
    switch (this) {
      case Currency.dollars:
        return '\$';
    }
  }
}

@immutable
class Item {
  final IconData icon;
  final String name;
  final double price;
  final Currency currency;

  const Item({
    required this.icon,
    required this.name,
    required this.price,
    required this.currency,
  });

  String get description => '$price${currency.title}';
}

const items = [
  Item(
    icon: Icons.camera_alt,
    name: 'Camera',
    price: 300,
    currency: Currency.dollars,
  ),
  Item(
    icon: Icons.house,
    name: 'House',
    price: 1000000,
    currency: Currency.dollars,
  ),
  Item(
    icon: Icons.watch,
    name: 'Smart Watch',
    price: 200,
    currency: Currency.dollars,
  ),
];

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Home Page'),
      ),
      body: ListView.builder(
        itemCount: items.length,
        itemBuilder: (_, index) {
          return ItemTile(
            item: items[index],
          );
        },
      ),
    );
  }
}

class ItemTile extends StatelessWidget {
  final Item item;
  const ItemTile({Key? key, required this.item}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(8.0),
      child: Stack(
        children: [
          const TileBackground(),
          CustomTile(item: item),
        ],
      ),
    );
  }
}

class CustomTile extends StatelessWidget {
  final Item item;
  const CustomTile({
    Key? key,
    required this.item,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.only(bottom: 7.0),
      child: Container(
        decoration: customDecoration(),
        child: ListTile(
          leading: Icon(
            item.icon,
            color: Colors.white,
          ),
          title: Text(item.name),
          subtitle: Text(item.description),
        ),
      ),
    );
  }
}

BoxDecoration customDecoration() {
  return BoxDecoration(
    color: const Color.fromARGB(255, 0x7d, 0xcf, 0xff),
    borderRadius: BorderRadius.circular(10.0),
    border: Border.all(
      color: Colors.black,
      width: 2.0,
    ),
  );
}

class TileBackground extends StatelessWidget {
  const TileBackground({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Positioned.fill(
      child: Padding(
        padding: const EdgeInsets.symmetric(horizontal: 6.0),
        child: Container(
          decoration: BoxDecoration(
            color: const Color.fromARGB(255, 202, 255, 127),
            borderRadius: BorderRadius.circular(10.0),
            border: Border.all(
              color: Colors.black,
              width: 2.0,
            ),
          ),
        ),
      ),
    );
  }
}

Transparent AppBar in Flutter



const images = [
  'https://bit.ly/3x7J5Qt',
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3qYOtDm',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3yvFg7X',
  'https://bit.ly/3ywzOla',
  'https://bit.ly/3wnASpW',
  'https://bit.ly/3jXSDto',
];

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      extendBodyBehindAppBar: true,
      appBar: AppBar(
        elevation: 0.0,
        backgroundColor: Colors.blueAccent.withAlpha(200),
        title: const Text('Transparent App Bar in Flutter'),
      ),
      body: const ImagesScrollView(),
    );
  }
}

class ImagesScrollView extends StatelessWidget {
  const ImagesScrollView({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SingleChildScrollView(
      padding: const EdgeInsets.only(top: 80.0),
      child: Padding(
        padding: const EdgeInsets.only(
          top: 40.0,
          left: 10.0,
          right: 10.0,
        ),
        child: Column(
          children: images
              .map((url) => ElevatedNetworkImage(url: url))
              .expand(
                (img) => [
                  img,
                  const SizedBox(height: 30.0),
                ],
              )
              .toList(),
        ),
      ),
    );
  }
}

class ElevatedNetworkImage extends StatelessWidget {
  final String url;
  const ElevatedNetworkImage({Key? key, required this.url}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return PhysicalShape(
      color: Colors.white,
      clipper: Clipper(),
      elevation: 20.0,
      clipBehavior: Clip.none,
      shadowColor: Colors.white.withAlpha(200),
      child: CutEdges(
        child: Image.network(url),
      ),
    );
  }
}

class Clipper extends CustomClipper<Path> {
  static const variance = 0.2;
  static const reverse = 1.0 - variance;

  @override
  Path getClip(Size size) {
    final path = Path();

    path.moveTo(0.0, size.height * Clipper.variance);
    path.lineTo(size.width * Clipper.variance, 0.0);
    path.lineTo(size.width, 0.0);
    path.lineTo(size.width, size.height * Clipper.reverse);
    path.lineTo(size.width * Clipper.reverse, size.height);
    path.lineTo(0.0, size.height);
    path.lineTo(0.0, size.height * Clipper.variance);
    path.close();
    return path;
  }

  @override
  bool shouldReclip(covariant CustomClipper<Path> oldClipper) => false;
}

class CutEdges extends StatelessWidget {
  final Widget child;

  const CutEdges({Key? key, required this.child}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return ClipPath(
      clipper: Clipper(),
      child: child,
    );
  }
}

Constructors on Abstract Classes in Dart



import 'dart:developer' as devtools show log;

extension Log on Object {
  void log() => devtools.log(toString());
}

enum Type { dog, cat }

abstract class CanRun {
  final Type type;
  const CanRun({required this.type});
}

class Cat extends CanRun {
  const Cat() : super(type: Type.cat);
}

class Dog extends CanRun {
  const Dog() : super(type: Type.dog);
}

@useResult in Dart



import 'package:meta/meta.dart' show useResult;

class Person {
  final String firstName;
  final String lastName;

  const Person({
    required this.firstName,
    required this.lastName,
  });

  @useResult
  String fullName() => '$firstName $lastName';
}

void printFullName() {
  const Person(
    firstName: 'Foo',
    lastName: 'Bar',
  ).fullName();
}

@mustCallSuper in Dart



class Animal {
  @mustCallSuper
  void run() {}
}

class Dog extends Animal {
  @override
  void run() {}
}

Object.hash in Dart



class BreadCrumb {
  final bool isActive;
  final String name;
  BreadCrumb({
    required this.isActive,
    required this.name,
  });
  BreadCrumb activated() => BreadCrumb(
        isActive: true,
        name: name,
      );
  @override
  bool operator ==(covariant BreadCrumb other) =>
      isActive == other.isActive && name == other.name;

  @override
  int get hashCode => Object.hash(isActive, name);
}

Expanded Equally in Flutter



import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      debugShowCheckedModeBanner: false,
      home: const HomePage(),
    ),
  );
}

extension ExpandEqually on Iterable<Widget> {
  Iterable<Widget> expandedEqually() => map(
        (w) => Expanded(
          flex: 1,
          child: w,
        ),
      );
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Home Page'),
      ),
      body: Column(
        children: [
          Row(
            mainAxisSize: MainAxisSize.max,
            children: [
              Container(
                height: 200,
                color: Colors.yellow,
              ),
              Container(
                height: 200,
                color: Colors.blue,
              ),
            ].expandedEqually().toList(),
          )
        ],
      ),
    );
  }
}

Random Iterable Value in Dart



import 'dart:math' as math show Random;

extension RandomElement<T> on Iterable<T> {
  T getRandomElement() => elementAt(
        math.Random().nextInt(length),
      );
}

final colors = [Colors.blue, Colors.red, Colors.brown];

class HomePage extends StatelessWidget {
  final color = ValueNotifier<MaterialColor>(
    colors.getRandomElement(),
  );
  HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('List.Random in Flutter'),
      ),
      body: ColorPickerButton(color: color),
    );
  }
}

class ColorPickerButton extends StatelessWidget {
  final ValueNotifier<MaterialColor> color;

  const ColorPickerButton({
    Key? key,
    required this.color,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return ValueListenableBuilder<Color>(
      valueListenable: color,
      builder: (context, value, child) {
        return Padding(
          padding: const EdgeInsets.all(8.0),
          child: CenteredTight(
            child: TextButton(
              style: TextButton.styleFrom(backgroundColor: value),
              onPressed: () {
                color.value = colors.getRandomElement();
              },
              child: const Text(
                'Change color',
                style: TextStyle(
                  fontSize: 30,
                  color: Colors.white,
                ),
              ),
            ),
          ),
        );
      },
    );
  }
}

Hardcoded Strings in Flutter



extension Hardcoded on String {
  String get hardcoded => '$this 🧨';
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(
          'My hardcoded string'.hardcoded,
        ),
      ),
      body: Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Text('String in body'.hardcoded),
        ],
      ),
    );
  }
}

Manually Scroll in List View in Flutter

// Free Flutter Course 💙 https://linktr.ee/vandadnp

import 'package:scrollable_positioned_list/scrollable_positioned_list.dart';

class HomePage extends StatelessWidget {
  final _controller = ItemScrollController();
  HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Testing'),
      ),
      body: ScrollablePositionedList.builder(
        itemScrollController: _controller,
        itemCount: allImages.length + 1,
        itemBuilder: (context, index) {
          if (index == 0) {
            return IndexSelector(
              count: allImages.length,
              onSelected: (index) {
                _controller.scrollTo(
                  index: index + 1,
                  duration: const Duration(milliseconds: 370),
                );
              },
            );
          } else {
            return ImageWithTitle(index: index);
          }
        },
      ),
    );
  }
}

class ImageWithTitle extends StatelessWidget {
  final int index;
  const ImageWithTitle({
    Key? key,
    required this.index,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Text(
          'Image $index',
          style: const TextStyle(fontSize: 30.0),
        ),
        Image.network(allImages.elementAt(index - 1)),
      ],
    );
  }
}

typedef OnIndexSelected = void Function(int index);

class IndexSelector extends StatelessWidget {
  final int count;
  final OnIndexSelected onSelected;
  final String prefix;
  const IndexSelector({
    Key? key,
    required this.count,
    required this.onSelected,
    this.prefix = 'Image',
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SingleChildScrollView(
      scrollDirection: Axis.horizontal,
      child: Row(
        children: Iterable.generate(
          count,
          (index) => TextButton(
            onPressed: () {
              onSelected(index);
            },
            child: Text('$prefix ${index + 1}'),
          ),
        ).toList(),
      ),
    );
  }
}

const imageUrls = [
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3qYOtDm',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3yvFg7X',
  'https://bit.ly/3ywzOla',
  'https://bit.ly/3wnASpW',
  'https://bit.ly/3jXSDto',
];

AsyncSnapshot to Widget in Flutter



import 'package:flutter/material.dart';
import 'package:flutter_hooks/flutter_hooks.dart';

void main() {
  runApp(
    MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const HomePage(),
    ),
  );
}

final future = Future<String>.delayed(
  const Duration(seconds: 3),
  () => 'Hello world',
);

typedef ResolveToWidget<T> = Widget Function(
  ConnectionState connectionState,
  AsyncSnapshot<T> snapshot,
);

extension Materialize on AsyncSnapshot {
  Widget materialize(ResolveToWidget f) => f(
        connectionState,
        this,
      );
}

class HomePage extends HookWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Hooks'),
      ),
      body: useFuture(future).materialize((connectionState, snapshot) {
        switch (connectionState) {
          case ConnectionState.done:
            return Text(snapshot.data ?? '');
          default:
            return const CircularProgressIndicator();
        }
      }),
    );
  }
}

Breadcrumbs in Flutter



@immutable
class BreadCrumbPath {
  final String title;
  final bool isActive;
  const BreadCrumbPath({
    required this.title,
    required this.isActive,
  });
  BreadCrumbPath activated() {
    return BreadCrumbPath(
      title: title,
      isActive: true,
    );
  }

  @override
  String toString() => title;
}

class BreatCrumbPathView extends StatelessWidget {
  final BreadCrumbPath path;

  const BreatCrumbPathView({
    Key? key,
    required this.path,
  }) : super(key: key);
  @override
  Widget build(BuildContext context) {
    final title = path.isActive ? '${path.title} →' : path.title;
    return Padding(
      padding: const EdgeInsets.all(2.0),
      child: Text(
        title,
        style: TextStyle(
          height: 1.0,
          fontSize: 20.0,
          color: path.isActive ? Colors.blueAccent : Colors.black,
        ),
      ),
    );
  }
}

typedef OnBreadCrumbPathTapped = void Function(BreadCrumbPath path);

class BreadCrumbView extends StatelessWidget {
  final OnBreadCrumbPathTapped onTapped;
  final Stream<List<BreadCrumbPath>> paths;
  const BreadCrumbView({
    Key? key,
    required this.paths,
    required this.onTapped,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return StreamBuilder<List<BreadCrumbPath>>(
      stream: paths,
      builder: (context, snapshot) {
        final List<Widget> views;
        switch (snapshot.connectionState) {
          case ConnectionState.waiting:
          case ConnectionState.active:
            final paths = snapshot.data ?? [];
            final views = paths
                .map(
                  (path) => GestureDetector(
                    onTap: () => onTapped(path),
                    child: BreatCrumbPathView(path: path),
                  ),
                )
                .toList();
            return Wrap(
              spacing: 4.0,
              children: views,
              alignment: WrapAlignment.start,
              crossAxisAlignment: WrapCrossAlignment.center,
            );
          default:
            return Wrap();
        }
      },
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  List<BreadCrumbPath> _paths = [];
  late final TextEditingController _textController;
  late final StreamController<List<BreadCrumbPath>> _pathsController;

  @override
  void initState() {
    _pathsController = StreamController<List<BreadCrumbPath>>.broadcast(
      onListen: () {
        _pathsController.add(_paths);
      },
    );
    _textController = TextEditingController();
    super.initState();
  }

  @override
  void dispose() {
    _textController.dispose();
    _pathsController.close();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Breadcrumb in Flutter'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(16.0),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            BreadCrumbView(
              paths: _pathsController.stream,
              onTapped: (path) async {
                await showBreadCrumbPathTappedDialog(
                  context,
                  path,
                );
              },
            ),
            TextField(
              controller: _textController,
              textAlign: TextAlign.center,
              decoration: const InputDecoration(
                hintText: 'Enter a new path here',
              ),
            ),
            TextButton(
              onPressed: () {
                _paths = [
                  ..._paths.map((p) => p.activated()),
                  BreadCrumbPath(
                    title: _textController.text,
                    isActive: false,
                  ),
                ];
                _pathsController.add(_paths);
                _textController.clear();
              },
              child: const Center(
                child: Text('Add new path'),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

Future<void> showBreadCrumbPathTappedDialog(
  BuildContext context,
  BreadCrumbPath path,
) {
  return showDialog(
    context: context,
    builder: (context) {
      return AlertDialog(
        content: Text('You tapped on $path'),
        actions: [
          TextButton(
            onPressed: () {
              Navigator.of(context).pop();
            },
            child: const Text('OK'),
          ),
        ],
      );
    },
  );
}

Unique Map Values in Dart



import 'dart:developer' as devtools show log;

extension ContainsDuplicateValues on Map {
  bool get containsDuplicateValues => 
    {...values}.length != values.length;
}

extension Log on Object {
  void log() => devtools.log(toString());
}

const people1 = {
  1: 'Foo',
  2: 'Bar',
};
const people2 = {
  1: 'Foo',
  2: 'Foo',
};

void testIt() {
  people1.containsDuplicateValues.log(); // false
  people2.containsDuplicateValues.log(); // true
}

Smart Quotes/Dashes in Flutter



class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Smart Quotes/Dashes in Flutter'),
      ),
      body: const Padding(
        padding: EdgeInsets.all(16.0),
        child: TextField(
          smartQuotesType: SmartQuotesType.disabled,
          smartDashesType: SmartDashesType.disabled,
          maxLines: null,
        ),
      ),
    );
  }
}

Haptic Feedback in Flutter



class CenteredTight extends StatelessWidget {
  final Widget child;
  const CenteredTight({
    Key? key,
    required this.child,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Row(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [child],
    );
  }
}

class FullscreenImage extends StatefulWidget {
  final String imageUrl;
  const FullscreenImage({Key? key, required this.imageUrl}) : super(key: key);

  @override
  State<FullscreenImage> createState() => _FullscreenImageState();
}

class _FullscreenImageState extends State<FullscreenImage> {
  var shouldDisplayAppbar = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: shouldDisplayAppbar ? AppBar(title: const Text('Image')) : null,
      body: GestureDetector(
        onTap: () {
          setState(() => shouldDisplayAppbar = !shouldDisplayAppbar);
        },
        child: Image.network(
          widget.imageUrl,
          alignment: Alignment.center,
          width: double.infinity,
          height: double.infinity,
          fit: BoxFit.cover,
        ),
      ),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Haptic Feedback in Flutter'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(16.0),
        child: CenteredTight(
          child: FractionallySizedBox(
            heightFactor: 0.7,
            child: GestureDetector(
              onLongPress: () async {
                await HapticFeedback.lightImpact();
                Navigator.of(context).push(
                  MaterialPageRoute(
                    builder: (context) {
                      return const FullscreenImage(
                        imageUrl: imageUrl,
                      );
                    },
                  ),
                );
              },
              child: Image.network(imageUrl),
            ),
          ),
        ),
      ),
    );
  }
}

Localization Delegates in Flutter



import 'package:flutter_gen/gen_l10n/app_localizations.dart';

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(
    MaterialApp(
      localizationsDelegates: AppLocalizations.localizationsDelegates,
      supportedLocales: AppLocalizations.supportedLocales,
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: BlocProvider<AuthBloc>(
        create: (context) => AuthBloc(FirebaseAuthProvider()),
        child: const HomePage(),
      ),
      routes: {
        createOrUpdateNoteRoute: (context) => const CreateUpdateNoteView(),
      },
    ),
  );
}

Extending Functions in Dart



import 'dart:developer' as devtools show log;

extension ToTextButton on VoidCallback {
  TextButton toTextButton(String title) {
    return TextButton(
      onPressed: this,
      child: Text(title),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Extensions in Flutter'),
      ),
      body: () {
        devtools.log('I am pressed');
      }.toTextButton('Press me'),
    );
  }
}

Paginated ListView in Flutter



@immutable
class Season {
  final String name;
  final String imageUrl;
  const Season({required this.name, required this.imageUrl});
  const Season.spring()
      : name = 'Spring',
        imageUrl = 'https://cnn.it/3xu58Ap';
  const Season.summer()
      : name = 'Summer',
        imageUrl = 'https://bit.ly/2VcCSow';
  const Season.autumn()
      : name = 'Autumn',
        imageUrl = 'https://bit.ly/3A3zStC';
  const Season.winter()
      : name = 'Winter',
        imageUrl = 'https://bit.ly/2TNY7wi';
}

const allSeasons = [
  Season.spring(),
  Season.summer(),
  Season.autumn(),
  Season.winter()
];

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    final width = MediaQuery.of(context).size.width;
    final height = width / (16.0 / 9.0);
    return Scaffold(
      appBar: AppBar(
        title: const Text('PageScrollPhysics in Flutter'),
      ),
      body: SizedBox(
        width: width,
        height: height,
        child: ListView(
          shrinkWrap: true,
          scrollDirection: Axis.horizontal,
          physics: const PageScrollPhysics(),
          clipBehavior: Clip.antiAlias,
          children: allSeasons.map((season) {
            return SizedBox(
              width: width,
              height: height,
              child: Image.network(
                season.imageUrl,
                height: height,
                fit: BoxFit.cover,
              ),
            );
          }).toList(),
        ),
      ),
    );
  }
}

Immutable Classes in Dart



import 'package:flutter/foundation.dart' show immutable;

@immutable
abstract class Animal {
  final String name;
  const Animal(this.name);
}

class Cat extends Animal {
  const Cat() : super('Cindy Clawford');
}

class Dog extends Animal {
  int age;
  Dog()
      : age = 0,
        super('Bark Twain');
}

Card Widget in Flutter



class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Card in Flutter'),
      ),
      body: Image.network(
        'https://bit.ly/36fNNj9',
        frameBuilder: (context, child, frame, wasSynchronouslyLoaded) {
          return Card(
            child: child,
            clipBehavior: Clip.antiAlias,
          );
        },
        loadingBuilder: (context, child, loadingProgress) {
          final totalBytes = loadingProgress?.expectedTotalBytes;
          final bytesLoaded = loadingProgress?.cumulativeBytesLoaded;
          if (totalBytes != null && bytesLoaded != null) {
            return Row(
              mainAxisAlignment: MainAxisAlignment.center,
              children: const [CircularProgressIndicator()],
            );
          } else {
            return child;
          }
        },
      ),
    );
  }
}

List Equality Ignoring Ordering in Dart



@immutable
class Person {
  final String name;
  const Person(this.name);

  @override
  bool operator ==(covariant Person other) => other.name == name;

  @override
  int get hashCode => name.hashCode;

  @override
  String toString() => name;
}

const people1 = [Person('Foo'), Person('Bar'), Person('Baz')];
const people2 = [Person('Foo'), Person('Bar'), Person('Baz')];
const people3 = [Person('Bar'), Person('Bar'), Person('Baz')];
const people4 = [Person('Bar'), Person('Baz')];

extension IsEqualToIgnoringOrdering<T> on List<T> {
  bool isEqualToIgnoringOrdering(List<T> other) =>
      length == other.length &&
      {...this}.intersection({...other}).length == length;
}

void testIt() {
  assert(people1.isEqualToIgnoringOrdering(people2));
  assert(!people1.isEqualToIgnoringOrdering(people3));
  assert(!people2.isEqualToIgnoringOrdering(people3));
  assert(!people3.isEqualToIgnoringOrdering(people4));
}

Shorten GitHub URLs in Dart

// Want to support my work 🤝? https://buymeacoffee.com/vandad

import 'dart:developer' as devtools show log;
import 'dart:convert' show utf8;

Future<Uri> shortenGitHubUrl(String longUrl) =>
    HttpClient().postUrl(Uri.parse('https://git.io/')).then((req) {
      req.add(utf8.encode('url=$longUrl'));
      return req.close();
    }).then(
      (resp) async {
        try {
          final location = resp.headers[HttpHeaders.locationHeader]?.first;
          if (location != null) {
            return Uri.parse(location);
          } else {
            throw 'No location was specified';
          }
        } catch (e) {
          return Uri.parse(longUrl);
        }
      },
    );

void testIt() async {
  final uri = await shortenGitHubUrl(
      'https://github.com/vandadnp/flutter-tips-and-tricks');
  devtools.log(uri.toString());
  // logs https://git.io/JS5Fm
}

Time Picker in Flutter



class HomePage extends StatelessWidget {
  final timeOfDay = ValueNotifier<TimeOfDay?>(null);
  HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return ValueListenableBuilder(
      valueListenable: timeOfDay,
      builder: (context, value, child) {
        final title = timeOfDay.value?.toString() ?? 'Time Picker in Flutter';
        return Scaffold(
          appBar: AppBar(title: Text(title)),
          body: Center(
            child: TextButton(
              onPressed: () async {
                timeOfDay.value = await showTimePicker(
                  context: context,
                  initialTime: TimeOfDay.now(),
                  initialEntryMode: TimePickerEntryMode.input,
                );
              },
              child: const Text('Please Pick a time'),
            ),
          ),
        );
      },
    );
  }
}

Throttled Print in Flutter



Stream<String> getStream() => Stream.periodic(
      const Duration(milliseconds: 100),
      (e) => DateTime.now().toString(),
    );

void testIt() async {
  await for (final now in getStream()) {
    debugPrintThrottled(now);
  }
}

Map Equality in Dart



typedef Name = String;
typedef Age = int;

const Map<Name, Age> people1 = {
  'foo': 20,
  'bar': 30,
  'baz': 40,
};

const Map<Name, Age> people2 = {
  'baz': 40,
  'foo': 20,
  'bar': 30,
};

void testIt() {
  assert(mapEquals(people1, people2));
}

Unique Maps in Dart



import 'dart:developer' as devtools show log;

typedef Name = String;
typedef Age = int;

const Map<Name, Age> people = {
  'foo': 20,
  'bar': 30,
  'baz': 20,
};

extension Unique<K, V> on Map<K, V> {
  Map<K, V> unique() {
    Map<K, V> result = {};
    for (final value in {...values}) {
      final firstKey = keys.firstWhereOrNull((key) => this[key] == value);
      if (firstKey != null) {
        result[firstKey] = value;
      }
    }
    return result;
  }
}

void testIt() {
  final uniques = people.unique();
  devtools.log(uniques.toString());
  // prints: {foo: 20, bar: 30}
}

Raw Auto Complete in Flutter



const emailProviders = [
  'gmail.com',
  'hotmail.com',
  'yahoo.com',
];

const icons = [
  'https://bit.ly/3HsvvvB',
  'https://bit.ly/3n6GW4L',
  'https://bit.ly/3zf2RLy',
];

class EmailTextField extends StatefulWidget {
  const EmailTextField({Key? key}) : super(key: key);

  @override
  State<EmailTextField> createState() => _EmailTextFieldState();
}

class _EmailTextFieldState extends State<EmailTextField> {
  late final TextEditingController _controller;
  late final FocusNode _focus;

  @override
  Widget build(BuildContext context) {
    return RawAutocomplete<String>(
      textEditingController: _controller,
      focusNode: _focus,
      fieldViewBuilder: (_, controller, focusNode, onSubmitted) {
        return TextFormField(
          controller: controller,
          focusNode: focusNode,
          onFieldSubmitted: (value) {
            onSubmitted();
          },
        );
      },
      optionsBuilder: (textEditingValue) {
        final lastChar = textEditingValue.text.characters.last;
        if (lastChar == '@') {
          return emailProviders;
        } else {
          return [];
        }
      },
      optionsViewBuilder: (context, onSelected, options) {
        return OptionsList(
          onSelected: onSelected,
          options: options,
          controller: _controller,
        );
      },
    );
  }

  @override
  void initState() {
    _controller = TextEditingController();
    _focus = FocusNode();
    super.initState();
  }

  @override
  void dispose() {
    _focus.dispose();
    _controller.dispose();
    super.dispose();
  }
}

class OptionsList extends StatelessWidget {
  final Iterable<String> options;
  final AutocompleteOnSelected<String> onSelected;
  final TextEditingController controller;
  const OptionsList({
    Key? key,
    required this.onSelected,
    required this.options,
    required this.controller,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Align(
      alignment: Alignment.topLeft,
      child: Material(
        child: SizedBox(
          height: 150,
          child: ListView.builder(
            padding: const EdgeInsets.all(0.0),
            itemCount: options.length,
            itemBuilder: (context, index) {
              final option = options.elementAt(index);
              return GestureDetector(
                onTap: () => onSelected(controller.text + option),
                child: ListTile(
                  horizontalTitleGap: 2.0,
                  leading: Image.network(
                    icons[index],
                    width: 24,
                    height: 24,
                  ),
                  title: Text(option),
                ),
              );
            },
          ),
        ),
      ),
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Raw Auto Complete in Flutter'),
      ),
      body: const Padding(
        padding: EdgeInsets.all(16.0),
        child: EmailTextField(),
      ),
    );
  }
}

Title on Object in Dart



import 'dart:developer' as devtools show log;

extension CapTitle on Object {
  String get capitalizedTitle {
    String str;
    if (this is Enum) {
      str = (this as Enum).name;
    } else {
      str = toString();
    }
    return str[0].toUpperCase() + str.substring(1);
  }
}

enum EmailProviders { gmail, yahoo, hotmail }

void testIt() {
  EmailProviders.values.map((p) => p.capitalizedTitle).forEach(devtools.log);
  // prints these:
  // Gmail
  // Yahoo
  // Hotmail
}

Compute in Flutter



import 'dart:developer' as devtools show log;
import 'dart:convert' show utf8, json;

@immutable
class Person {
  final String name;
  final int age;
  const Person(this.name, this.age);
  Person.fromJson(Map<String, dynamic> json)
      : name = json["name"] as String,
        age = json["age"] as int;
}

Future<Iterable<Person>> downloadAndParsePersons(Uri uri) => HttpClient()
    .getUrl(uri)
    .then((req) => req.close())
    .then((response) => response.transform(utf8.decoder).join())
    .then((jsonString) => json.decode(jsonString) as List<dynamic>)
    .then((json) => json.map((map) => Person.fromJson(map)));

void testIt() async {
  final persons = await compute(
    downloadAndParsePersons,
    Uri.parse('https://bit.ly/3Jjcw8R'),
  );
  devtools.log(persons.toString());
}

Filter on Map in Dart



import 'dart:developer' as devtools show log;

typedef Name = String;
typedef Age = int;

extension Filter<K, V> on Map<K, V> {
  Iterable<MapEntry<K, V>> filter(
    bool Function(MapEntry<K, V> entry) f,
  ) sync* {
    for (final entry in entries) {
      if (f(entry)) {
        yield entry;
      }
    }
  }
}

const Map<Name, Age> people = {
  'foo': 20,
  'bar': 31,
  'baz': 25,
  'qux': 32,
};

void testIt() async {
  final peopleOver30 = people.filter((e) => e.value > 30);
  devtools.log(peopleOver30.toString());
  // ☝🏻 prints (MapEntry(bar: 31), MapEntry(qux: 32))
}

Type Alias in Dart



const Map<String, int> people1 = {
  'foo': 20,
  'bar': 30,
  'baz': 25,
};

typedef Age = int;

const Map<String, Age> people2 = {
  'foo': 20,
  'bar': 30,
  'baz': 25,
};

ValueNotifier in Flutter



class DynamicToolTipTextField extends StatelessWidget {
  final TextInputType? keyboardType;
  final ValueNotifier<String?> hint;
  final TextEditingController controller;
  const DynamicToolTipTextField({
    Key? key,
    required this.hint,
    required this.controller,
    this.keyboardType,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return ValueListenableBuilder(
      valueListenable: hint,
      builder: (context, value, child) {
        return TextField(
          keyboardType: keyboardType,
          controller: controller,
          decoration: InputDecoration(
            hintText: value as String?,
          ),
        );
      },
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

@immutable
abstract class HasText {
  String get text;
}

enum Hint { pleaseEnterYourEmail, youForgotToEnterYourEmail }

extension GetText on Hint {
  String get text {
    switch (this) {
      case Hint.pleaseEnterYourEmail:
        return 'Please enter your email';
      case Hint.youForgotToEnterYourEmail:
        return 'You forgot to enter your email';
    }
  }
}

class _HomePageState extends State<HomePage> {
  late final ValueNotifier<String?> _hint;
  late final TextEditingController _controller;

  @override
  void initState() {
    _hint = ValueNotifier<String?>(Hint.pleaseEnterYourEmail.text);
    _controller = TextEditingController();
    super.initState();
  }

  @override
  void dispose() {
    _hint.dispose();
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('ValueNotifier in Flutter'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(8.0),
        child: Column(
          children: [
            DynamicToolTipTextField(
              hint: _hint,
              controller: _controller,
              keyboardType: TextInputType.emailAddress,
            ),
            TextButton(
              onPressed: () async {
                final email = _controller.text;
                if (email.trim().isEmpty) {
                  _hint.value = Hint.youForgotToEnterYourEmail.text;
                  await Future.delayed(const Duration(seconds: 2));
                  _hint.value = Hint.pleaseEnterYourEmail.text;
                }
              },
              child: const Text('Log in'),
            )
          ],
        ),
      ),
    );
  }
}

Object to Integer in Dart



enum ToIntStrategy { round, floor, ceil }

typedef ToIntOnErrorHandler = int Function(Object e);

extension ToInt on Object {
  int toInteger({
    ToIntStrategy strategy = ToIntStrategy.round,
    ToIntOnErrorHandler? onError,
  }) {
    try {
      final doubleValue = double.parse(toString());
      switch (strategy) {
        case ToIntStrategy.round:
          return doubleValue.round();
        case ToIntStrategy.floor:
          return doubleValue.floor();
        case ToIntStrategy.ceil:
          return doubleValue.ceil();
      }
    } catch (e) {
      if (onError != null) {
        return onError(e);
      } else {
        return -1;
      }
    }
  }
}

void testIt() {
  assert('xyz'.toInteger(onError: (_) => 100) == 100);
  assert(1.5.toInteger() == 2);
  assert(1.6.toInteger() == 2);
  assert('1.2'.toInteger(strategy: ToIntStrategy.floor) == 1);
  assert('1.2'.toInteger(strategy: ToIntStrategy.ceil) == 2);
  assert('1.5'.toInteger(strategy: ToIntStrategy.round) == 2);
}

Image Opacity in Flutter



class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage>
    with SingleTickerProviderStateMixin {
  late final AnimationController _controller;
  late final Animation<double> _opacity;

  @override
  void initState() {
    _controller = AnimationController(
      vsync: this,
      duration: const Duration(seconds: 1),
    );
    _opacity = Tween(begin: 0.0, end: 1.0).animate(_controller);
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        children: [
          Image.network(
            'https://bit.ly/3ywI8l6',
            opacity: _opacity,
          ),
          Slider(
            value: _controller.value,
            onChanged: (value) {
              setState(() => _controller.value = value);
            },
          ),
        ],
      ),
    );
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }
}

Covariant in Dart

// Want to support my work 🤝? https://buymeacoffee.com/vandad

class Person {
  final String name;
  const Person(this.name);
  @override
  bool operator ==(Object other) {
    if (other is! Person) throw ArgumentError('Was expecting a person');
    return other.name == name;
  }

  @override
  int get hashCode => name.hashCode;
}

class Person {
  final String name;
  const Person(this.name);
  @override
  bool operator ==(covariant Person other) => other.name == name;

  @override
  int get hashCode => name.hashCode;
}

Custom Errors in Streams in Dart



class Either<V, E extends Exception> {
  final V? value;
  final E? error;

  const Either({this.value, this.error}) : assert((value ?? error) != null);

  bool get isError => error != null;
  bool get isValue => value != null;

  @override
  String toString() {
    if (value != null) {
      return "Value: $value";
    } else if (error != null) {
      return "Error: $error";
    } else {
      return 'Unknown state';
    }
  }
}

class DateTimeException implements Exception {
  final String reason;
  const DateTimeException({required this.reason});
}

Stream<Either<DateTime, DateTimeException>> getDateTime() async* {
  var index = 0;
  while (true) {
    if (index % 2 == 0) {
      yield Either(value: DateTime.now());
    } else {
      yield const Either(
        error: DateTimeException(reason: 'Something is wrong!'),
      );
    }
    index += 1;
  }
}

void testIt() async {
  await for (final value in getDateTime()) {
    dev.log(value.toString());
  }
}

Shake Animation in Flutter



class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

const animationWidth = 10.0;

class _HomePageState extends State<HomePage>
    with SingleTickerProviderStateMixin {
  late final TextEditingController _textController;
  late final AnimationController _animationController;
  late final Animation<double> _offsetAnim;
  final defaultHintText = 'Please enter your email here 😊';
  var _hintText = '';

  @override
  void initState() {
    _hintText = defaultHintText;
    _textController = TextEditingController();
    _animationController = AnimationController(
      duration: const Duration(milliseconds: 370),
      vsync: this,
    );
    _offsetAnim = Tween(
      begin: 0.0,
      end: animationWidth,
    ).chain(CurveTween(curve: Curves.elasticIn)).animate(
          _animationController,
        )..addStatusListener(
        (status) {
          if (status == AnimationStatus.completed) {
            _animationController.reverse();
          }
        },
      );
    super.initState();
  }

  @override
  void dispose() {
    _textController.dispose();
    _animationController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Shake Animation in Flutter'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(8.0),
        child: Column(
          children: [
            AnimatedBuilder(
              animation: _offsetAnim,
              builder: (context, child) {
                return Container(
                  margin: const EdgeInsets.symmetric(
                    horizontal: animationWidth,
                  ),
                  padding: EdgeInsets.only(
                    left: _offsetAnim.value + animationWidth,
                    right: animationWidth - _offsetAnim.value,
                  ),
                  child: TextField(
                    controller: _textController,
                    keyboardType: TextInputType.emailAddress,
                    decoration: InputDecoration(
                      hintText: _hintText,
                    ),
                  ),
                );
              },
            ),
            TextButton(
                onPressed: () async {
                  if (_textController.text.isEmpty) {
                    setState(() {
                      _hintText = 'You forgot to enter your email 🥲';
                      _animationController.forward(from: 0.0);
                    });
                    await Future.delayed(const Duration(seconds: 3));
                    setState(() {
                      _hintText = defaultHintText;
                    });
                  }
                },
                child: const Text('Login'))
          ],
        ),
      ),
    );
  }
}

Throw Enums in Dart



import 'dart:developer' as dev show log;

enum Exceptions { invalidUserName, invalidPassword }

void thisMethodThrows() {
  throw Exceptions.invalidPassword;
}

void testIt() {
  try {
    thisMethodThrows();
  } on Exceptions catch (e) {
    switch (e) {
      case (Exceptions.invalidUserName):
        dev.log("Invalid user name");
        break;
      case (Exceptions.invalidPassword):
        dev.log("Invalid password");
        break;
    }
  }
}

Future Error Test in Flutter



import 'dart:developer' as dev show log;

@immutable
abstract class UserException implements Exception {}

class InvalidUserNameException extends UserException {}

class InvalidUserAgeException extends UserException {}

@immutable
class User {
  final String name;
  final int age;
  User({required this.name, required this.age}) {
    if (!name.contains(RegExp(r'^[a-z ]+$'))) {
      throw InvalidUserNameException();
    } else if (age < 0 || age > 130) {
      throw InvalidUserAgeException();
    }
  }
  const User.anonymous()
      : name = 'Anonymous User',
        age = 0;
}

Future<User> getAsyncUser() => Future.delayed(
      const Duration(seconds: 1),
      () => User(name: 'Foo', age: 20),
    );

void testIt() async {
  final user = await getAsyncUser()
      .catchError(
        handleInvalidUsernameException,
        test: (e) => e is InvalidUserNameException,
      )
      .catchError(
        handleInvalidAgeException,
        test: (e) => e is InvalidUserAgeException,
      );
  dev.log(user.toString());
}

User handleInvalidUsernameException(Object? e) {
  dev.log(e.toString());
  return const User.anonymous();
}

User handleInvalidAgeException(Object? e) {
  dev.log(e.toString());
  return const User.anonymous();
}

Generic URL Retrieval in Dart



import 'dart:developer' as dev show log;

typedef StatusCodeResultBuilder<T> = Future<T> Function(
  int statusCode,
  HttpClientResponse response,
);

extension Get on Uri {
  Future<T?> getBody<T>({
    StatusCodeResultBuilder<T>? statusBuilder,
    T Function(Object error)? onNetworkError,
  }) async {
    try {
      final apiCall = await HttpClient().getUrl(this);
      final response = await apiCall.close();
      final builder = statusBuilder;
      if (builder == null) {
        final data = await response.transform(convert.utf8.decoder).join();
        if (data is T) {
          return data as T?;
        } else {
          return null;
        }
      } else {
        final result = await builder(response.statusCode, response);
        return result;
      }
    } catch (e) {
      if (onNetworkError != null) {
        return onNetworkError(e);
      } else {
        return null;
      }
    }
  }
}

extension ToUri on String {
  Uri toUri() => Uri.parse(this);
}

const url = 'https://bit.ly/3EKWcLa';

void testIt() async {
  final json = await url.toUri().getBody<String>(
    statusBuilder: (statusCode, response) async {
      if (statusCode == 200) {
        return await response.transform(convert.utf8.decoder).join();
      } else {
        return "{'error': 'Unexpected status code $statusCode'}";
      }
    },
    onNetworkError: (error) {
      return "{'error': 'Got network error'}";
    },
  );
  if (json != null) {
    dev.log(json);
  }
}

Custom Error Widget in Flutter



class MyErrorWidget extends StatelessWidget {
  final String text;
  const MyErrorWidget({Key? key, required this.text}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SizedBox(
        width: MediaQuery.of(context).size.width,
        child: Padding(
          padding: const EdgeInsets.all(16.0),
          child: Column(
            mainAxisAlignment: MainAxisAlignment.start,
            children: [
              Image.network('https://bit.ly/3gHlTCU'),
              Text(
                text,
                textAlign: TextAlign.center,
                style: const TextStyle(
                  color: Colors.red,
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

void main() {
  ErrorWidget.builder = (FlutterErrorDetails details) {
    bool isInDebugMode = false;
    assert(() {
      isInDebugMode = true;
      return true;
    }());
    final message = details.exception.toString();
    if (isInDebugMode) {
      return MyErrorWidget(text: message);
    } else {
      return Text(
        message,
        textAlign: TextAlign.center,
      );
    }
  };

  runApp(
    const MaterialApp(
      home: HomePage(),
      debugShowCheckedModeBanner: false,
    ),
  );
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Error Widget in Flutter'),
      ),
      body: Builder(
        builder: (context) {
          throw Exception(
              'Here is an exception that is caught by our custom Error Widget in Flutter');
        },
      ),
    );
  }
}

Handle Multiple Future Errors in Dart



import 'dart:developer' as dev show log;

Future<Iterable<T>> waitOn<T>(
  Iterable<Future<T>> futures,
  Function onError,
) async {
  List<T> result = [];
  for (final future in futures) {
    final value = await future.catchError(onError);
    result.add(value);
  }
  return result;
}

void testIt() async {
  final f1 = Future.error('First Error');
  final f2 = Future.delayed(const Duration(seconds: 2), () => 10);
  final f3 = Future.error('Second error');
  final f4 = Future.delayed(const Duration(seconds: 2), () => 'Hello world');
  final result = await waitOn([f1, f2, f3, f4], (error) => -1);
  dev.log(result.toString()); // [-1, 10, -1, Hello world]
}

Future Error Handling in Dart

import 'dart:developer' as dev show log;

extension OnError<T> on Future<T> {
  Future<T> onErrorJustReturn(T value) => catchError((_) => value);
}

Future<bool> isUserRegistered({required String email}) => HttpClient()
    .postUrl(Uri.parse('https://website'))
    .then((req) {
      req.headers.add('email', email);
      return req.close();
    })
    .then((resp) => resp.statusCode == 200)
    .onErrorJustReturn(false);

void testIt() async {
  final isFooRegistered = await isUserRegistered(email: 'foo@flutter.com');
  dev.log(isFooRegistered.toString());
}

String to Toast in Flutter



extension Toast on String {
  Future<void> showAsToast(BuildContext context,
      {required Duration duration}) async {
    final scaffold = ScaffoldMessenger.of(context);
    final controller = scaffold.showSnackBar(
      SnackBar(
        content: Text(this),
        backgroundColor: const Color(0xFF24283b),
        behavior: SnackBarBehavior.floating,
        elevation: 2.0,
        shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.circular(10),
        ),
      ),
    );
    await Future.delayed(duration);
    controller.close();
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: TextButton(
          onPressed: () => 'Hello, World!'.showAsToast(
            context,
            duration: const Duration(seconds: 2),
          ),
          child: const Text('Show the snackbar'),
        ),
      ),
    );
  }
}

Waiting in Dart



Future<void> wait(Duration d) async {
  await Future.delayed(d);
}

extension Wait on int {
  Future<void> get seconds => wait(Duration(seconds: this));
  Future<void> get minutes => wait(Duration(minutes: this));
}

void testIt() async {
  await 2.seconds;
  'After 2 seconds'.log();
  await 3.minutes;
  'After 3 minutes'.log();
}

extension Log on Object {
  void log() {
    dev.log(toString());
  }
}

Loading Dialog in Flutter



typedef CloseDialog = void Function();

CloseDialog showLoadingScreen({
  required BuildContext context,
  required String text,
}) {
  final dialog = AlertDialog(
    content: Column(
      mainAxisSize: MainAxisSize.min,
      children: [
        const CircularProgressIndicator(),
        const SizedBox(height: 10),
        Text(text),
      ],
    ),
  );
  showDialog(
    context: context,
    barrierDismissible: false,
    builder: (_) => dialog,
  );

  return () => Navigator.of(context).pop();
}

void testIt(BuildContext context) async {
  final closeDialog = showLoadingScreen(
    context: context,
    text: 'Loading data...',
  );
  await Future.delayed(const Duration(seconds: 2));
  closeDialog();
}

Compact Map on Map<K,V> in Dart



const foo = 'foo';
const bar = 'bar';
const baz = 'baz';

const namesAndAges = {
  foo: 20,
  bar: 25,
  baz: 18,
};

const acceptedNames = [
  foo,
  bar,
];

void testIt() {
  final acceptedAges = namesAndAges.compactMap(
    (e) => acceptedNames.contains(e.key) ? e.value : null,
  );
  acceptedAges.log(); // [20, 25]
}

extension CompactMap<T, E> on Map<T, E> {
  Iterable<V> compactMap<V>(V? Function(MapEntry<T, E>) f) sync* {
    for (final entry in entries) {
      final extracted = f(entry);
      if (extracted != null) {
        yield extracted;
      }
    }
  }
}

Query Parameters in Dart



import 'dart:developer' as devtools show log;

const host = 'freecurrencyapi.net';
const path = '/api/v2/latest';
const apiKey = 'YOUR_API_KEY';
const baseCurrency = 'sek';
const params = {
  'apiKey': apiKey,
  'base_currency': 'sek',
};

void insteadOfThis() {
  const url = 'https://$host$path?apiKey=$apiKey&base_currency=$baseCurrency';
  url.log();
}

void doThis() {
  final url = Uri.https(host, path, params);
  url.log();
}

extension Log on Object {
  void log() {
    devtools.log(toString());
  }
}

Multiple Gradients in Container in Flutter



typedef GradientContainersBuilder = Map<LinearGradient, Widget?> Function();

class GradientContainers extends StatelessWidget {
  final GradientContainersBuilder builder;

  const GradientContainers({
    Key? key,
    required this.builder,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Stack(
      children: builder().entries.map((mapEntry) {
        final gradient = mapEntry.key;
        final widget = mapEntry.value;
        return GradientContainer(
          gradient: gradient,
          child: widget,
        );
      }).toList(),
    );
  }
}

class GradientContainer extends StatelessWidget {
  final LinearGradient gradient;
  final Widget? child;

  const GradientContainer({Key? key, required this.gradient, this.child})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Positioned.fill(
      child: Container(
        decoration: BoxDecoration(
          gradient: gradient,
        ),
        child: child,
      ),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: GradientContainers(
        builder: () => {
          topLeftToBottomRightGradient: null,
          rightToLeftGradient: null,
          leftToRightGradinet: null,
          bottomRightGradient: Image.network('https://bit.ly/3otHHog'),
        },
      ),
    );
  }
}

const transparent = Color(0x00FFFFFF);

const topLeftToBottomRightGradient = LinearGradient(
  begin: Alignment.topLeft,
  end: Alignment.bottomRight,
  colors: [
    Color(0xff2ac3de),
    transparent,
  ],
);

const bottomRightGradient = LinearGradient(
  begin: Alignment.bottomRight,
  end: Alignment.topLeft,
  colors: [
    Color(0xffbb9af7),
    transparent,
  ],
);

const rightToLeftGradient = LinearGradient(
  begin: Alignment.centerRight,
  end: Alignment.centerLeft,
  colors: [
    Color(0xff9ece6a),
    transparent,
  ],
);

const leftToRightGradinet = LinearGradient(
  begin: Alignment.centerLeft,
  end: Alignment.centerRight,
  colors: [
    Color(0xff7dcfff),
    transparent,
  ],
);

void main() {
  runApp(
    const MaterialApp(
      home: HomePage(),
      debugShowCheckedModeBanner: false,
    ),
  );
}

Filter on Stream<List<T>> in Dart



import 'dart:developer' as devtools show log;

extension Filter<T> on Stream<List<T>> {
  Stream<List<T>> filter(bool Function(T) where) =>
      map((items) => items.where(where).toList());
}

final Stream<List<int>> allNumbers = Stream.periodic(
  const Duration(seconds: 1),
  (value) => [for (var i = 0; i < value; i++) i],
);

bool isEven(num value) => value % 2 == 0;
bool isOdd(num value) => value % 2 != 0;

extension EvenOdd<E extends num> on Stream<List<E>> {
  Stream<List<E>> get evenNumbers => filter(isEven);
  Stream<List<E>> get oddNumbers => filter(isOdd);
}

void readEvenNumbers() async {
  await for (final evenNumber in allNumbers.evenNumbers) {
    devtools.log('All even numbers: $evenNumber');
  }
}

void readOddNumbers() async {
  await for (final oddNumber in allNumbers.oddNumbers) {
    devtools.log('All odd numbers: $oddNumber');
  }
}

Generic Route Arguments in Flutter

extension GetArgument on BuildContext {
  T? getArgument<T>() {
    final modalRoute = ModalRoute.of(this);
    if (modalRoute != null) {
      final args = modalRoute.settings.arguments;
      if (args != null && args is T) {
        return args as T;
      }
    }
    return null;
  }
}

Generic Dialog in Flutter

typedef DialogOptionBuilder<T> = Map<String, T> Function();

Future<T?> showGenericDialog<T>({
  required BuildContext context,
  required String title,
  required String content,
  required DialogOptionBuilder optionsBuilder,
}) {
  final options = optionsBuilder();
  return showDialog<T>(
    context: context,
    builder: (context) {
      return AlertDialog(
        title: Text(title),
        content: Text(content),
        actions: options.keys.map(
          (optionTitle) {
            final T value = options[optionTitle];
            return TextButton(
              onPressed: () {
                Navigator.of(context).pop(value);
              },
              child: Text(optionTitle),
            );
          },
        ).toList(),
      );
    },
  );
}

Future<bool> showLogOutDialog(BuildContext context) {
  return showGenericDialog<bool>(
    context: context,
    title: 'Log out',
    content: 'Are you sure you want to log out?',
    optionsBuilder: () => {
      'Cancel': false,
      'Log out': true,
    },
  ).then(
    (value) => value ?? false,
  );
}

GitHub API in Flutter



import 'dart:io' show HttpHeaders, HttpClient;
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'dart:convert' show utf8, json;

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

Future<Iterable<GithubUser>> getGithubFollowers(String accessToken) =>
    HttpClient()
        .getUrl(Uri.parse('https://api.github.com/user/followers'))
        .then((req) {
          req.headers
            ..set(HttpHeaders.authorizationHeader, 'Bearer $accessToken')
            ..set(HttpHeaders.contentTypeHeader, 'application/json');
          return req.close();
        })
        .then((resp) => resp.transform(utf8.decoder).join())
        .then((jsonStr) => json.decode(jsonStr) as List<dynamic>)
        .then(
          (jsonArray) => jsonArray.compactMap((element) {
            if (element is Map<String, dynamic>) {
              return element;
            } else {
              return null;
            }
          }),
        )
        .then(
          (listOfMaps) => listOfMaps.map(
            (map) => GithubUser.fromJson(map),
          ),
        );

class GithubUser {
  final String username;
  final String avatarUrl;

  GithubUser.fromJson(Map<String, dynamic> json)
      : username = json['login'] as String,
        avatarUrl = json['avatar_url'] as String;
}

extension CompactMap<T> on List<T> {
  List<E> compactMap<E>(E? Function(T element) f) {
    Iterable<E> imp(E? Function(T element) f) sync* {
      for (final value in this) {
        final mapped = f(value);
        if (mapped != null) {
          yield mapped;
        }
      }
    }

    return imp(f).toList();
  }
}

const token = 'PUT_YOUR_TOKEN_HERE';

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('GitHub API in Flutter'),
      ),
      body: FutureBuilder(
        future: getGithubFollowers(token),
        builder: (context, snapshot) {
          switch (snapshot.connectionState) {
            case ConnectionState.done:
              final users = (snapshot.data as Iterable<GithubUser>).toList();
              return ListView.builder(
                itemCount: users.length,
                itemBuilder: (context, index) {
                  final user = users[index];
                  return ListTile(
                    title: Text(user.username),
                    leading: CircularAvatar(url: user.avatarUrl),
                  );
                },
              );
            default:
              return const CircularProgressIndicator();
          }
        },
      ),
    );
  }
}

void main() {
  runApp(
    const MaterialApp(
      home: HomePage(),
      debugShowCheckedModeBanner: false,
    ),
  );
}

ChangeNotifier in Flutter



import 'package:provider/provider.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

const allImages = [
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3qYOtDm',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3yvFg7X',
  'https://bit.ly/3ywzOla',
  'https://bit.ly/3wnASpW',
  'https://bit.ly/3jXSDto',
];

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class ImageData {
  final Uint8List imageData;
  const ImageData(this.imageData);
}

class Images extends ChangeNotifier {
  final List<ImageData> _items = [];

  var _isLoading = false;
  bool get isLoading => _isLoading;

  UnmodifiableListView<ImageData> get items => UnmodifiableListView(_items);

  void loadNextImage() async {
    if (_items.length < allImages.length) {
      // time to load more
      _isLoading = true;
      notifyListeners();
      final imageUrl = allImages[_items.length];
      final networkAsset = NetworkAssetBundle(Uri.parse(imageUrl));
      final loaded = await networkAsset.load(imageUrl);
      final bytes = loaded.buffer.asUint8List();
      final imageData = ImageData(bytes);
      _items.insert(0, imageData);
      _isLoading = false;
      notifyListeners();
    } else {
      if (isLoading) {
        _isLoading = false;
        notifyListeners();
      }
    }
  }
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('ChangeNotifier in Flutter'),
        actions: [
          Consumer<Images>(
            builder: (context, value, child) {
              return IconButton(
                onPressed: () {
                  value.loadNextImage();
                },
                icon: const Icon(Icons.add_box_outlined),
              );
            },
          )
        ],
      ),
      body: Padding(
        padding: const EdgeInsets.all(16.0),
        child: Consumer<Images>(
          builder: (context, value, child) {
            final images = value.items;
            final isLoading = value.isLoading;
            return ListView.builder(
              itemBuilder: (context, index) {
                if (index == 0 && isLoading) {
                  return Center(
                    child: Column(
                      children: const [
                        CircularProgressIndicator(),
                        SizedBox(height: 16.0),
                      ],
                    ),
                  );
                } else {
                  final imageIndex = isLoading ? index - 1 : index;
                  final imageData = images[imageIndex].imageData;
                  return Column(
                    children: [
                      RoundedImageWithShadow(imageData: imageData),
                      const SizedBox(height: 16.0),
                    ],
                  );
                }
              },
              itemCount: isLoading ? images.length + 1 : images.length,
            );
          },
        ),
      ),
    );
  }
}

class RoundedImageWithShadow extends StatelessWidget {
  final Uint8List imageData;
  const RoundedImageWithShadow({Key? key, required this.imageData})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      clipBehavior: Clip.antiAlias,
      decoration: BoxDecoration(
        borderRadius: BorderRadius.circular(20),
        boxShadow: [
          BoxShadow(
            blurRadius: 2,
            color: Colors.black.withAlpha(40),
            spreadRadius: 2,
          ),
        ],
      ),
      child: Image.memory(
        imageData,
        fit: BoxFit.cover,
      ),
    );
  }
}

void main() {
  runApp(
    MaterialApp(
      home: ChangeNotifierProvider(
        create: (_) => Images(),
        child: const HomePage(),
      ),
      debugShowCheckedModeBanner: false,
    ),
  );
}

Refresh Indicator in Flutter



import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

const allImages = [
  'https://bit.ly/3x7J5Qt',
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3qYOtDm',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3yvFg7X',
  'https://bit.ly/3ywzOla',
  'https://bit.ly/3wnASpW',
  'https://bit.ly/3jXSDto',
];

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  final _images = [allImages.first];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Refresh Indicator in Flutter'),
      ),
      body: RefreshIndicator(
        onRefresh: () async {
          final nextIndex = _images.length + 1;
          if (nextIndex < allImages.length) {
            setState(() {
              _images.insert(0, allImages[nextIndex]);
            });
          }
        },
        child: ListView.builder(
          physics: const AlwaysScrollableScrollPhysics(),
          padding: const EdgeInsets.all(16),
          itemCount: _images.length,
          itemBuilder: (context, index) {
            final imageUrl = _images[index];
            return Column(
              children: [
                RoundedImageWithShadow(url: imageUrl),
                const SizedBox(height: 16),
              ],
            );
          },
        ),
      ),
    );
  }
}

class RoundedImageWithShadow extends StatelessWidget {
  final String url;
  const RoundedImageWithShadow({Key? key, required this.url}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      clipBehavior: Clip.antiAlias,
      decoration: BoxDecoration(
        borderRadius: BorderRadius.circular(20),
        boxShadow: [
          BoxShadow(
            blurRadius: 2,
            color: Colors.black.withAlpha(40),
            spreadRadius: 2,
          ),
        ],
      ),
      child: Image.network(url),
    );
  }
}

FlatMap in Dart



extension FlatMap<T> on T? {
  E? flatMap<E>(E? Function(T) f) => this != null ? f(this!) : null;
}

AuthUser? get insteadOfThis {
  final user = FirebaseAuth.instance.currentUser;
  if (user != null) {
    return AuthUser.fromFirebase(user);
  } else {
    return null;
  }
}

AuthUser? get doThis =>
    FirebaseAuth.instance.currentUser.flatMap((u) => AuthUser.fromFirebase(u));

OrientationBuilder in Flutter



import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

class RoundedImageWithShadow extends StatelessWidget {
  final String url;
  const RoundedImageWithShadow({Key? key, required this.url}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      clipBehavior: Clip.antiAlias,
      decoration: BoxDecoration(
        borderRadius: BorderRadius.circular(20),
        boxShadow: [
          BoxShadow(
            blurRadius: 2,
            color: Colors.black.withAlpha(40),
            spreadRadius: 2,
          ),
        ],
      ),
      child: Image.network(url),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: OrientationBuilder(
          builder: (context, orientation) {
            final int count;
            switch (orientation) {
              case Orientation.portrait:
                count = 2;
                break;
              case Orientation.landscape:
                count = 4;
                break;
            }
            return GridView.count(
              padding: const EdgeInsets.all(8.0),
              crossAxisCount: count,
              mainAxisSpacing: 8.0,
              crossAxisSpacing: 8.0,
              children: images
                  .map((url) => RoundedImageWithShadow(url: url))
                  .toList(),
            );
          },
        ),
      ),
    );
  }
}

final images = [
  'https://bit.ly/3qJ2FCf',
  'https://bit.ly/3Hs9JsV',
  'https://bit.ly/3cfT6Cv',
  'https://bit.ly/30wGnIE',
  'https://bit.ly/3kJYsum',
  'https://bit.ly/3oDoMaJ',
  'https://bit.ly/3FndXQM',
  'https://bit.ly/3ci4i1f',
];

Linear Gradient in Flutter



import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Linear Gradient in Flutter'),
      ),
      body: const ImageWithShadow(url: 'https://bit.ly/3otHHog'),
    );
  }
}

class ImageWithShadow extends StatelessWidget {
  final String url;

  const ImageWithShadow({
    Key? key,
    required this.url,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(16.0),
      child: Stack(
        children: [
          Positioned.fill(
            child: Container(
              decoration: BoxDecoration(
                boxShadow: [
                  BoxShadow(
                    blurRadius: 10.0,
                    color: Colors.black.withOpacity(0.5),
                    offset: const Offset(0.0, 3.0),
                  )
                ],
                borderRadius: const BorderRadius.all(Radius.circular(20)),
                gradient: const LinearGradient(
                  begin: Alignment.topCenter,
                  end: Alignment.bottomCenter,
                  colors: [
                    Color.fromARGB(255, 176, 229, 251),
                    Color.fromARGB(255, 235, 202, 250)
                  ],
                ),
              ),
            ),
          ),
          Image.network(url),
        ],
      ),
    );
  }
}

Bloc Text Editing Controller in Flutter

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:bloc/bloc.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

abstract class Event {
  const Event();
}

class SearchEvent extends Event {
  final String searchString;
  const SearchEvent(this.searchString);
}

class ClearSearch extends Event {}

class SearchBloc extends Bloc<Event, List<String>> {
  static const names = ['foo', 'bar', 'baz'];

  SearchBloc() : super(names) {
    on<Event>((event, emit) {
      if (event is SearchEvent) {
        emit(names
            .where((element) => element.contains(event.searchString))
            .toList());
      } else if (event is ClearSearch) {
        emit(names);
      }
    });
  }
}

class BlocTextEditingController extends TextEditingController {
  SearchBloc? bloc;
  BlocTextEditingController() {
    addListener(() {
      if (text.isEmpty) {
        bloc?.add(ClearSearch());
      } else {
        bloc?.add(SearchEvent(text));
      }
    });
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

const largeStyle = TextStyle(fontSize: 30);

class _HomePageState extends State<HomePage> {
  late final BlocTextEditingController _controller;

  @override
  void initState() {
    _controller = BlocTextEditingController();
    super.initState();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    _controller.bloc = BlocProvider.of<SearchBloc>(context);
    return Scaffold(
      appBar: AppBar(
        title: Text('Bloc Search in Flutter'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(8.0),
        child: BlocBuilder<SearchBloc, List<String>>(
          builder: (context, state) {
            return ListView.builder(
              itemBuilder: (context, index) {
                if (index == 0) {
                  // search field
                  return TextField(
                    decoration: InputDecoration(
                      hintText: 'Enter search term here...',
                      hintStyle: largeStyle,
                    ),
                    style: largeStyle,
                    controller: _controller,
                  );
                } else {
                  final name = state[index - 1];
                  return ListTile(
                    title: Text(
                      name,
                      style: largeStyle,
                    ),
                  );
                }
              },
              itemCount: state.length + 1, // +1 for search
            );
          },
        ),
      ),
    );
  }
}

Blurred TabBar in Flutter



import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

const images = [
  'https://bit.ly/3x7J5Qt',
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3qYOtDm',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3yvFg7X',
  'https://bit.ly/3ywzOla',
  'https://bit.ly/3wnASpW',
  'https://bit.ly/3jXSDto',
];

class CustomTabBar extends StatelessWidget {
  final List<IconButton> buttons;

  const CustomTabBar({Key? key, required this.buttons}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Align(
      alignment: Alignment.bottomCenter,
      child: ClipRect(
        child: Container(
          height: 80,
          color: Colors.white.withOpacity(0.4),
          child: BackdropFilter(
            filter: ImageFilter.blur(sigmaX: 4.0, sigmaY: 4.0),
            child: Container(
              width: double.infinity,
              decoration: BoxDecoration(
                color: Colors.white.withOpacity(0.5),
              ),
              child: Padding(
                padding: const EdgeInsets.only(bottom: 15),
                child: Row(
                  crossAxisAlignment: CrossAxisAlignment.center,
                  mainAxisAlignment: MainAxisAlignment.spaceAround,
                  children: buttons,
                ),
              ),
            ),
          ),
        ),
      ),
    );
  }
}

const summerIcon = Icon(
  Icons.surfing,
  size: 40.0,
  color: Colors.teal,
);

const autumnIcon = Icon(
  Icons.nature_outlined,
  size: 40.0,
  color: Colors.black45,
);

const winterIcon = Icon(
  Icons.snowboarding,
  size: 40.0,
  color: Colors.black45,
);

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Blurred Tab Bar'),
      ),
      body: Stack(
        children: [
          ListView.builder(
            itemCount: images.length,
            itemBuilder: (context, index) {
              final url = images[index];
              return Image.network(url);
            },
          ),
          CustomTabBar(
            buttons: [
              IconButton(
                icon: summerIcon,
                onPressed: () {
                  // implement me
                },
              ),
              IconButton(
                icon: autumnIcon,
                onPressed: () {
                  // implement me
                },
              ),
              IconButton(
                icon: winterIcon,
                onPressed: () {
                  // implement me
                },
              )
            ],
          )
        ],
      ),
    );
  }
}

Play YouTube in Flutter



import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:webview_flutter/webview_flutter.dart';

const videoIds = [
  'BHACKCNDMW8',
  '26h9hBZFl7w',
  'glENND73k4Q',
  'd0tU18Ybcvk',
];

class VideoView extends StatelessWidget {
  final String videoId;
  final _key = UniqueKey();

  VideoView({required this.videoId});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Watch a Video'),
      ),
      body: Center(
        child: Container(
          height: 232.0,
          child: WebView(
            key: _key,
            initialUrl: 'https://www.youtube.com/embed/$videoId',
            javascriptMode: JavascriptMode.unrestricted,
          ),
        ),
      ),
    );
  }
}

class YouTubeVideoThumbnail extends StatelessWidget {
  final String videoId;
  final String thumbnailUrl;

  const YouTubeVideoThumbnail({Key? key, required this.videoId})
      : thumbnailUrl = 'https://img.youtube.com/vi/$videoId/maxresdefault.jpg',
        super(key: key);

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: () {
        Navigator.of(context).push(
          MaterialPageRoute(
            builder: (_) => VideoView(videoId: videoId),
          ),
        );
      },
      child: Container(
        height: 256.0,
        clipBehavior: Clip.antiAlias,
        decoration: BoxDecoration(
          boxShadow: [
            BoxShadow(
              blurRadius: 10.0,
              color: Colors.black.withAlpha(50),
              spreadRadius: 10.0,
            ),
          ],
          borderRadius: BorderRadius.circular(20),
          image: DecorationImage(
            fit: BoxFit.fitHeight,
            image: NetworkImage(thumbnailUrl),
          ),
        ),
        child: Center(
          child: Icon(
            Icons.play_arrow,
            color: Colors.white,
            size: 100.0,
          ),
        ),
      ),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('YouTube Videos in Flutter')),
      body: ListView.builder(
        itemCount: videoIds.length,
        itemBuilder: (context, index) {
          final videoId = videoIds[index];
          return Padding(
            padding: const EdgeInsets.all(8.0),
            child: YouTubeVideoThumbnail(videoId: videoId),
          );
        },
      ),
    );
  }
}

ListView Background in Flutter



import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

class ListItem {
  const ListItem();
  factory ListItem.emptyTile() => EmptyTile();
  factory ListItem.tile(
    String title,
    String subTitle,
  ) =>
      Tile(
        title,
        subTitle,
      );
}

class Tile extends ListItem {
  final String title;
  final String subTitle;
  const Tile(this.title, this.subTitle) : super();
}

class EmptyTile extends ListItem {}

final items = [
  for (var i = 1; i <= 6; i++) ListItem.tile('Title $i', 'Sub title $i'),
  ListItem.emptyTile(),
  for (var i = 7; i <= 12; i++) ListItem.tile('Title $i', 'Sub title $i'),
];

class Background extends StatelessWidget {
  final Widget child;
  const Background({Key? key, required this.child}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return Container(
      clipBehavior: Clip.antiAlias,
      decoration: BoxDecoration(
        borderRadius: BorderRadius.circular(20),
        image: DecorationImage(
          fit: BoxFit.fitHeight,
          image: NetworkImage('https://bit.ly/3jXSDto'),
        ),
      ),
      child: child,
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Background(
        child: ListView.builder(
          padding: EdgeInsets.zero,
          itemCount: items.length,
          itemBuilder: (context, index) {
            final item = items[index];
            if (item is Tile) {
              return Container(
                color: Colors.grey[200],
                child: ListTile(
                  title: Text(item.title),
                  subtitle: Text(item.subTitle),
                ),
              );
            } else if (item is EmptyTile) {
              return SizedBox(
                height: 450,
              );
            } else {
              throw 'unexpcted item';
            }
          },
        ),
      ),
    );
  }
}

Integer to Binary in Dart

extension ToBinary on int {
  String toBinary(
    int len, {
    int separateAtLength = 4,
    String separator = ',',
  }) =>
      toRadixString(2)
          .padLeft(len, '0')
          .splitByLength(separateAtLength)
          .join(separator);
}

void testIt() {
  assert(1.toBinary(8) == '0000,0001');
  assert(2.toBinary(4) == '0010');
  assert(3.toBinary(16) == '0000,0000,0000,0011');
  assert(255.toBinary(8, separateAtLength: 8) == '11111111');
  assert(255.toBinary(8, separateAtLength: 4) == '1111,1111');
}

extension SplitByLength on String {
  Iterable<String> splitByLength(int len, {String filler = '0'}) sync* {
    final missingFromLength =
        length % len == 0 ? 0 : len - (characters.length % len);
    final expectedLength = length + missingFromLength;
    final src = padLeft(expectedLength, filler);
    final chars = src.characters;
    for (var i = 0; i < chars.length; i += len) {
      yield chars.getRange(i, i + len).toString();
    }
  }
}

Split String by Length in Dart



void testIt() {
  assert('dartlang'
      .splitByLength(5, filler: '💙')
      .isEqualTo(['💙💙dar', 'tlang']));

  assert('0100010'.splitByLength(4).isEqualTo(['0010', '0010']));
  assert('foobar'.splitByLength(3).isEqualTo(['foo', 'bar']));
  assert('flutter'.splitByLength(4, filler: 'X').isEqualTo(['Xflu', 'tter']));
  assert('dart'.splitByLength(5, filler: '').isEqualTo(['dart']));
}

extension SplitByLength on String {
  Iterable<String> splitByLength(int len, {String filler = '0'}) sync* {
    final missingFromLength =
        length % len == 0 ? 0 : len - (characters.length % len);
    final expectedLength = length + missingFromLength;
    final src = padLeft(expectedLength, filler);
    final chars = src.characters;
    for (var i = 0; i < chars.length; i += len) {
      yield chars.getRange(i, i + len).toString();
    }
  }
}

Image Tint in Flutter



import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

enum OverlayColor { brown, orange, yellow, green, blue }

extension Color on OverlayColor {
  MaterialColor get color {
    switch (this) {
      case OverlayColor.blue:
        return Colors.blue;
      case OverlayColor.brown:
        return Colors.brown;
      case OverlayColor.green:
        return Colors.green;
      case OverlayColor.orange:
        return Colors.orange;
      case OverlayColor.yellow:
        return Colors.yellow;
    }
  }
}

extension Title on OverlayColor {
  String get title => toString().split('.').last;
}

extension ToTextButtonWithValue on OverlayColor {
  TextButtonWithValue<OverlayColor> toTextButtonWithValue(
      OnTextButtonWithValuePressed onPressed) {
    return TextButtonWithValue(
      value: this,
      onPressed: onPressed,
      child: Text(title),
    );
  }
}

typedef OnTextButtonWithValuePressed<T> = void Function(T value);

class TextButtonWithValue<T> extends StatelessWidget {
  final T value;
  final OnTextButtonWithValuePressed onPressed;
  final Widget child;
  const TextButtonWithValue({
    Key? key,
    required this.value,
    required this.onPressed,
    required this.child,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return TextButton(
      onPressed: () {
        onPressed(value);
      },
      child: child,
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  OverlayColor? _overlayColor;

  ColorFilter? getcolorFilter() {
    final overlayColor = _overlayColor;
    if (overlayColor == null) {
      return null;
    }
    return ColorFilter.mode(
      overlayColor.color,
      BlendMode.colorBurn,
    );
  }

  Iterable<Widget> overlayColorButtons() {
    return OverlayColor.values.map((overlayColor) {
      return Expanded(
        flex: 1,
        child: Container(
          child: overlayColor.toTextButtonWithValue(
            (value) {
              setState(() {
                _overlayColor = value;
              });
            },
          ),
        ),
      );
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Tinting Images in Flutter'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(16.0),
        child: Column(
          children: [
            Container(
              height: 250.0,
              clipBehavior: Clip.antiAlias,
              decoration: BoxDecoration(
                borderRadius: BorderRadius.circular(20),
                image: DecorationImage(
                  colorFilter: getcolorFilter(),
                  fit: BoxFit.fitHeight,
                  image: NetworkImage('https://bit.ly/3jOueGG'),
                ),
              ),
            ),
            SizedBox(height: 16.0),
            Row(
              children: overlayColorButtons().toList(),
            )
          ],
        ),
      ),
    );
  }
}

SlideTransition in Flutter



import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:flutter/gestures.dart';

class _HomePageState extends State<HomePage>
    with SingleTickerProviderStateMixin {
  late final _controller = AnimationController(
    duration: Duration(milliseconds: 500),
    vsync: this,
  );

  late final _animation = Tween<Offset>(
    begin: Offset(0.0, 0.0),
    end: Offset(-0.83, 0.0),
  ).animate(
    CurvedAnimation(
      parent: _controller,
      curve: Curves.easeInQuint,
    ),
  );

  var _isExpanded = false;

  @override
  void dispose() {
    super.dispose();
    _controller.dispose();
  }

  @override
  Widget build(BuildContext context) {
    _controller.forward();
    return Scaffold(
      body: SizedBox.expand(
        child: Stack(
          fit: StackFit.passthrough,
          children: [
            Image.network(
              'https://bit.ly/3BWYDbz',
              fit: BoxFit.fitHeight,
            ),
            Positioned(
              top: 200.0,
              child: SlideTransition(
                position: _animation,
                child: GestureDetector(
                  onTap: () {
                    _isExpanded = !_isExpanded;
                    if (_isExpanded) {
                      _controller.reverse();
                    } else {
                      _controller.forward();
                    }
                  },
                  child: Box(),
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class Box extends StatelessWidget {
  const Box({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      decoration: BoxDecoration(
        color: Colors.blue[200]?.withAlpha(200),
        border: Border.all(
          color: Colors.blue,
          style: BorderStyle.solid,
          width: 1.0,
        ),
        borderRadius: BorderRadius.only(
          topRight: Radius.circular(10),
          bottomRight: Radius.circular(10),
        ),
      ),
      child: Padding(
        padding: const EdgeInsets.all(8.0),
        child: Row(
          children: [
            Text(
              'By: Jesper Anhede',
              style: TextStyle(
                fontSize: 18.0,
              ),
            ),
            SizedBox(width: 10.0),
            Icon(
              Icons.info,
              color: Colors.pink[400],
            ),
          ],
        ),
      ),
    );
  }
}

Expansion Panels and Lists in Flutter



import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

class Event {
  final String title;
  final String details;
  final String imageUrl;
  bool isExpanded = false;

  Event({
    required this.title,
    required this.details,
    required this.imageUrl,
  });

  @override
  bool operator ==(covariant Event other) => title == other.title;
}

const diwaliDetails =
    '''Diwali, or Dipawali, is India's biggest and most important holiday of the year. The festival gets its name from the row (avali) of clay lamps (deepa) that Indians light outside their homes to symbolize the inner light that protects from spiritual darkness. This festival is as important to Hindus as the Christmas holiday is to Christians.''';

const halloweenDetails =
    '''Halloween or Hallowe'en, less commonly known as Allhalloween, All Hallows' Eve, or All Saints' Eve, is a celebration observed in many countries on 31 October, the eve of the Western Christian feast of All Hallows' Day.''';

final events = [
  Event(
    title: 'Diwali',
    details: diwaliDetails,
    imageUrl: 'https://bit.ly/3mGg8YW',
  ),
  Event(
    title: 'Halloween',
    details: halloweenDetails,
    imageUrl: 'https://bit.ly/3wb1w7j',
  ),
];

extension ToPanel on Event {
  ExpansionPanel toPanel() {
    return ExpansionPanel(
      headerBuilder: (context, isExpanded) {
        return Padding(
          padding: const EdgeInsets.all(8.0),
          child: Text(
            title,
            style: TextStyle(fontSize: 30.0),
          ),
        );
      },
      isExpanded: isExpanded,
      body: Container(
        height: 250,
        width: double.infinity,
        decoration: BoxDecoration(
          image: DecorationImage(
            fit: BoxFit.fitWidth,
            colorFilter: ColorFilter.mode(
              Colors.black.withOpacity(0.5),
              BlendMode.luminosity,
            ),
            image: NetworkImage(imageUrl),
          ),
        ),
        child: SingleChildScrollView(
          child: Padding(
            padding: const EdgeInsets.all(8.0),
            child: Text(
              details,
              textAlign: TextAlign.center,
              style: TextStyle(fontSize: 20, color: Colors.white, shadows: [
                Shadow(
                  blurRadius: 1.0,
                  offset: Offset.zero,
                  color: Colors.black,
                )
              ]),
            ),
          ),
        ),
      ),
    );
  }
}

class HomePage extends StatefulWidget {
  HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Expansion Panels in Flutter'),
      ),
      body: SingleChildScrollView(
        child: ExpansionPanelList(
          children: events.map((e) => e.toPanel()).toList(),
          expansionCallback: (panelIndex, isExpanded) {
            setState(() {
              events[panelIndex].isExpanded = !isExpanded;
            });
          },
        ),
      ),
    );
  }
}

Complete CRUD App in Flutter

//Want to support my work 🤝? https://buymeacoffee.com/vandad

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:path_provider/path_provider.dart';
import 'package:sqflite/sqflite.dart';
import 'package:path_provider/path_provider.dart'
    show getApplicationDocumentsDirectory;

class Person implements Comparable {
  final int id;
  final String firstName;
  final String lastName;
  const Person(this.id, this.firstName, this.lastName);

  String get fullName => '$firstName $lastName';

  Person.fromData(Map<String, Object?> data)
      : id = data['ID'] as int,
        firstName = data['FIRST_NAME'] as String,
        lastName = data['LAST_NAME'] as String;

  @override
  int compareTo(covariant Person other) => other.id.compareTo(id);

  @override
  bool operator ==(covariant Person other) => id == other.id;

  @override
  String toString() =>
      'Person, ID = $id, firstName = $firstName, lastName = $lastName';
}

class PersonDB {
  final _controller = StreamController<List<Person>>.broadcast();
  List<Person> _persons = [];
  Database? _db;
  final String dbName;
  PersonDB({required this.dbName});

  Future<bool> close() async {
    final db = _db;
    if (db == null) {
      return false;
    }
    await db.close();
    return true;
  }

  Future<bool> open() async {
    if (_db != null) {
      return true;
    }
    final directory = await getApplicationDocumentsDirectory();
    final path = '${directory.path}/$dbName';
    try {
      final db = await openDatabase(path);
      _db = db;

      // create the table if it doesn't exist

      final create = '''CREATE TABLE IF NOT EXISTS PEOPLE (
          ID INTEGER PRIMARY KEY AUTOINCREMENT,
          FIRST_NAME STRING NOT NULL,
          LAST_NAME STRING NOT NULL
        )''';

      await db.execute(create);

      // if everything went fine, we then read all the objects
      // and populate the stream

      _persons = await _fetchPeople();
      _controller.add(_persons);
      return true;
    } catch (e) {
      print('error = $e');
      return false;
    }
  }

  Future<List<Person>> _fetchPeople() async {
    final db = _db;
    if (db == null) {
      return [];
    }

    try {
      // read the existing data if any
      final readResult = await db.query(
        'PEOPLE',
        distinct: true,
        columns: ['ID', 'FIRST_NAME', 'LAST_NAME'],
        orderBy: 'ID',
      );

      final people = readResult.map((row) => Person.fromData(row)).toList();
      return people;
    } catch (e) {
      print('error = $e');
      return [];
    }
  }

  Future<bool> delete(Person person) async {
    final db = _db;
    if (db == null) {
      return false;
    }
    try {
      final deletedCount = await db.delete(
        'PEOPLE',
        where: 'ID = ?',
        whereArgs: [person.id],
      );

      // delete it locally as well

      if (deletedCount == 1) {
        _persons.remove(person);
        _controller.add(_persons);
        return true;
      } else {
        return false;
      }
    } catch (e) {
      print('Error inserting $e');
      return false;
    }
  }

  Future<bool> create(String firstName, String lastName) async {
    final db = _db;
    if (db == null) {
      return false;
    }
    try {
      final id = await db.insert(
        'PEOPLE',
        {
          'FIRST_NAME': firstName,
          'LAST_NAME': lastName,
        },
      );

      final person = Person(id, firstName, lastName);
      _persons.add(person);
      _controller.add(_persons);

      return true;
    } catch (e) {
      print('Error inserting $e');
      return false;
    }
  }

  // uses the person's id to update its first name and last name
  Future<bool> update(Person person) async {
    final db = _db;
    if (db == null) {
      return false;
    }
    try {
      final updatedCount = await db.update(
        'PEOPLE',
        {
          'FIRST_NAME': person.firstName,
          'LAST_NAME': person.lastName,
        },
        where: 'ID = ?',
        whereArgs: [person.id],
      );

      if (updatedCount == 1) {
        _persons.removeWhere((p) => p.id == person.id);
        _persons.add(person);
        _controller.add(_persons);
        return true;
      } else {
        return false;
      }
    } catch (e) {
      print('Error inserting $e');
      return false;
    }
  }

  Stream<List<Person>> all() =>
      _controller.stream.map((event) => event..sort());
}

typedef OnCompose = void Function(String firstName, String lastName);

class ComposeWidget extends StatefulWidget {
  final OnCompose onCompose;

  const ComposeWidget({Key? key, required this.onCompose}) : super(key: key);

  @override
  State<ComposeWidget> createState() => _ComposeWidgetState();
}

class _ComposeWidgetState extends State<ComposeWidget> {
  final firstNameController = TextEditingController();
  final lastNameController = TextEditingController();

  @override
  void dispose() {
    firstNameController.dispose();
    lastNameController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(8.0),
      child: Column(children: [
        TextField(
          style: TextStyle(fontSize: 24),
          decoration: InputDecoration(
            hintText: 'Enter first name',
          ),
          controller: firstNameController,
        ),
        TextField(
          style: TextStyle(fontSize: 24),
          decoration: InputDecoration(
            hintText: 'Enter last name',
          ),
          controller: lastNameController,
        ),
        TextButton(
          onPressed: () {
            final firstName = firstNameController.text;
            final lastName = lastNameController.text;
            widget.onCompose(firstName, lastName);
          },
          child: Text(
            'Add to list',
            style: TextStyle(fontSize: 24),
          ),
        ),
      ]),
    );
  }
}

class HomePage extends StatefulWidget {
  HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  late final PersonDB _crudStorage;

  @override
  void initState() {
    _crudStorage = PersonDB(dbName: 'db.sqlite');
    _crudStorage.open();
    super.initState();
  }

  @override
  void dispose() {
    _crudStorage.close();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('SQLite in Flutter'),
      ),
      body: StreamBuilder(
        stream: _crudStorage.all(),
        builder: (context, snapshot) {
          switch (snapshot.connectionState) {
            case ConnectionState.active:
            case ConnectionState.waiting:
              if (snapshot.data == null) {
                return Center(child: CircularProgressIndicator());
              }
              final people = snapshot.data as List<Person>;
              return Column(
                children: [
                  ComposeWidget(
                    onCompose: (firstName, lastName) async {
                      await _crudStorage.create(firstName, lastName);
                    },
                  ),
                  Expanded(
                    child: ListView.builder(
                      itemCount: people.length,
                      itemBuilder: (context, index) {
                        final person = people[index];
                        return ListTile(
                          onTap: () async {
                            final update =
                                await showUpdateDialog(context, person);
                            if (update == null) {
                              return;
                            }
                            await _crudStorage.update(update);
                          },
                          title: Text(
                            person.fullName,
                            style: TextStyle(fontSize: 24),
                          ),
                          subtitle: Text(
                            'ID: ${person.id}',
                            style: TextStyle(fontSize: 18),
                          ),
                          trailing: TextButton(
                            onPressed: () async {
                              final shouldDelete =
                                  await showDeleteDialog(context);
                              if (shouldDelete) {
                                await _crudStorage.delete(person);
                              }
                            },
                            child: Icon(
                              Icons.disabled_by_default_rounded,
                              color: Colors.red,
                            ),
                          ),
                        );
                      },
                    ),
                  ),
                ],
              );
            default:
              return Center(child: CircularProgressIndicator());
          }
        },
      ),
    );
  }
}

final firstNameController = TextEditingController();
final lastNameController = TextEditingController();

Future<Person?> showUpdateDialog(BuildContext context, Person person) {
  firstNameController.text = person.firstName;
  lastNameController.text = person.lastName;
  return showDialog(
    context: context,
    builder: (context) {
      return AlertDialog(
        content: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            Text('Enter your udpated values here:'),
            TextField(controller: firstNameController),
            TextField(controller: lastNameController),
          ],
        ),
        actions: [
          TextButton(
            onPressed: () {
              Navigator.of(context).pop(null);
            },
            child: Text('Cancel'),
          ),
          TextButton(
            onPressed: () {
              final newPerson = Person(
                person.id,
                firstNameController.text,
                lastNameController.text,
              );
              Navigator.of(context).pop(newPerson);
            },
            child: Text('Save'),
          ),
        ],
      );
    },
  ).then((value) {
    if (value is Person) {
      return value;
    } else {
      return null;
    }
  });
}

Future<bool> showDeleteDialog(BuildContext context) {
  return showDialog(
    context: context,
    builder: (context) {
      return AlertDialog(
        content: Text('Are you sure you want to delete this item?'),
        actions: [
          TextButton(
            onPressed: () {
              Navigator.of(context).pop(false);
            },
            child: Text('No'),
          ),
          TextButton(
            onPressed: () {
              Navigator.of(context).pop(true);
            },
            child: Text('Delete'),
          )
        ],
      );
    },
  ).then(
    (value) {
      if (value is bool) {
        return value;
      } else {
        return false;
      }
    },
  );
}

SQLite Storage in Flutter



import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:path_provider/path_provider.dart';
import 'package:sqflite/sqflite.dart';
import 'package:path_provider/path_provider.dart'
    show getApplicationDocumentsDirectory;

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class Person implements Comparable {
  final int id;
  final String firstName;
  final String lastName;
  const Person(this.id, this.firstName, this.lastName);

  String get fullName => '$firstName $lastName';

  Person.fromData(Map<String, Object?> data)
      : id = data['ID'] as int,
        firstName = data['FIRST_NAME'] as String,
        lastName = data['LAST_NAME'] as String;

  @override
  int compareTo(covariant Person other) => other.id.compareTo(id);
}

typedef OnCompose = void Function(String firstName, String lastName);

class ComposeWidget extends StatefulWidget {
  final OnCompose onCompose;

  const ComposeWidget({Key? key, required this.onCompose}) : super(key: key);

  @override
  State<ComposeWidget> createState() => _ComposeWidgetState();
}

class _ComposeWidgetState extends State<ComposeWidget> {
  final firstNameController = TextEditingController();
  final lastNameController = TextEditingController();

  @override
  void dispose() {
    firstNameController.dispose();
    lastNameController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(8.0),
      child: Column(children: [
        TextField(
          style: TextStyle(fontSize: 24),
          decoration: InputDecoration(
            hintText: 'Enter first name',
          ),
          controller: firstNameController,
        ),
        TextField(
          style: TextStyle(fontSize: 24),
          decoration: InputDecoration(
            hintText: 'Enter last name',
          ),
          controller: lastNameController,
        ),
        TextButton(
          onPressed: () {
            final firstName = firstNameController.text;
            final lastName = lastNameController.text;
            widget.onCompose(firstName, lastName);
          },
          child: Text(
            'Add to list',
            style: TextStyle(fontSize: 24),
          ),
        ),
      ]),
    );
  }
}

class _HomePageState extends State<HomePage> {
  late final Database db;
  bool hasSetUpAlready = false;

  Future<bool> setupDatabase() async {
    if (hasSetUpAlready == false) {
      final directory = await getApplicationDocumentsDirectory();
      final path = '${directory.path}/db.sqlite';
      try {
        db = await openDatabase(path);

        // create the table if it doesn't exist

        final create = '''CREATE TABLE IF NOT EXISTS PEOPLE (
          ID INTEGER PRIMARY KEY AUTOINCREMENT,
          FIRST_NAME STRING NOT NULL,
          LAST_NAME STRING NOT NULL
        )''';

        await db.execute(create);
        hasSetUpAlready = true;
        return true;
      } catch (e) {
        print('error = $e');
        hasSetUpAlready = false;
        return false;
      }
    } else {
      return true;
    }
  }

  Future<List<Person>> fetchPersons() async {
    if (!await setupDatabase()) {
      return [];
    }

    try {
      // read the existing data if any
      final readResult = await db.query(
        'PEOPLE',
        distinct: true,
        columns: ['ID', 'FIRST_NAME', 'LAST_NAME'],
        orderBy: 'ID',
      );

      final people = readResult.map((row) => Person.fromData(row)).toList()
        ..sort();
      return people;
    } catch (e) {
      print('error = $e');
      return [];
    }
  }

  Future<bool> addPerson(String firstName, String lastName) async {
    try {
      await db.insert(
        'PEOPLE',
        {
          'FIRST_NAME': firstName,
          'LAST_NAME': lastName,
        },
      );
      return true;
    } catch (e) {
      print('Error inserting $e');
      return false;
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('SQLite in Flutter'),
      ),
      body: FutureBuilder(
        future: fetchPersons(),
        builder: (context, snapshot) {
          switch (snapshot.connectionState) {
            case ConnectionState.done:
              final people = snapshot.data as List<Person>;
              return Column(
                children: [
                  ComposeWidget(
                    onCompose: (firstName, lastName) async {
                      await addPerson(firstName, lastName);
                      setState(() {});
                    },
                  ),
                  Expanded(
                    child: ListView.builder(
                      itemCount: people.length,
                      itemBuilder: (context, index) {
                        final person = people[index];
                        return ListTile(
                          title: Text(
                            person.fullName,
                            style: TextStyle(fontSize: 24),
                          ),
                          subtitle: Text(
                            'ID: ${person.id}',
                            style: TextStyle(fontSize: 18),
                          ),
                        );
                      },
                    ),
                  ),
                ],
              );
            default:
              return CircularProgressIndicator();
          }
        },
      ),
    );
  }
}

Circular Progress with Percentage in Flutter



import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

class SizedCircularProgressIndicator extends StatelessWidget {
  final double progress;
  final double width;
  final double height;
  final TextStyle? textStyle;
  const SizedCircularProgressIndicator({
    Key? key,
    this.textStyle,
    required this.progress,
    required this.width,
    required this.height,
  }) : super(key: key);

  TextStyle get style => textStyle ?? TextStyle(fontSize: 30.0);
  int get _progress => (progress * 100.0).toInt();

  @override
  Widget build(BuildContext context) {
    return Stack(
      alignment: Alignment.center,
      children: [
        Text('$_progress%', style: style),
        SizedBox(
          width: width,
          height: height,
          child: CircularProgressIndicator(
            backgroundColor: Colors.white70,
            value: progress,
            color: Colors.blueAccent,
            strokeWidth: 3.0,
          ),
        ),
      ],
    );
  }
}

const images = [
  'https://bit.ly/3x7J5Qt',
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3qYOtDm',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3yvFg7X',
  'https://bit.ly/3ywzOla',
  'https://bit.ly/3wnASpW',
  'https://bit.ly/3jXSDto',
];

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: PageView.builder(
        scrollDirection: Axis.horizontal,
        itemCount: images.length,
        itemBuilder: (context, index) {
          return WithBlurredBackground(imageUrl: images[index]);
        },
      ),
    );
  }
}

class WithBlurredBackground extends StatelessWidget {
  final String imageUrl;

  const WithBlurredBackground({Key? key, required this.imageUrl})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SizedBox.expand(
      child: Stack(
        alignment: Alignment.center,
        fit: StackFit.passthrough,
        children: [
          SizedBox.expand(
            child: ClipRect(
              child: ImageFiltered(
                imageFilter: ImageFilter.blur(
                  sigmaX: 10.0,
                  sigmaY: 10.0,
                ),
                child: Image.network(
                  imageUrl,
                  fit: BoxFit.fitHeight,
                ),
              ),
            ),
          ),
          NetworkImageWithProgress(url: imageUrl),
        ],
      ),
    );
  }
}

class NetworkImageWithProgress extends StatelessWidget {
  final String url;

  const NetworkImageWithProgress({Key? key, required this.url})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Image.network(
      url,
      loadingBuilder: (context, child, loadingProgress) {
        final totalBytes = loadingProgress?.expectedTotalBytes;
        final bytesLoaded = loadingProgress?.cumulativeBytesLoaded;
        if (totalBytes != null && bytesLoaded != null) {
          return SizedCircularProgressIndicator(
            height: 100,
            width: 100,
            progress: bytesLoaded / totalBytes,
          );
        } else {
          return child;
        }
      },
      errorBuilder: (context, error, stackTrace) {
        return Text('Error!');
      },
    );
  }
}

Opening URLs in Flutter



import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:url_launcher/url_launcher.dart';

class Person {
  final String profileUrl;
  final String name;
  final String email;
  final String phoneNumber;
  final String websiteUrl;

  const Person({
    Key? key,
    required this.profileUrl,
    required this.name,
    required this.email,
    required this.phoneNumber,
    required this.websiteUrl,
  });

  Person.vandad()
      : profileUrl = 'https://bit.ly/3jwusS0',
        name = 'Vandad Nahavandipoor',
        email = 'vandad.np@gmail.com',
        phoneNumber = '071234567',
        websiteUrl = 'https://pixolity.se';
}

void open(String url) async {
  if (await canLaunch(url)) {
    await launch(url);
  }
}

class PersonNameView extends StatelessWidget {
  final Person person;
  const PersonNameView(this.person, {Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Text(
      person.name,
      style: TextStyle(
        fontSize: 20,
        fontWeight: FontWeight.bold,
        color: Colors.black,
      ),
    );
  }
}

class PersonEmailView extends StatelessWidget {
  final Person person;
  const PersonEmailView(this.person, {Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return TextButton(
      onPressed: () {
        open('mailto:${person.email}');
      },
      child: Text(
        '💌 Email me',
        style: TextStyle(fontSize: 20.0),
      ),
    );
  }
}

class PersonPhoneView extends StatelessWidget {
  final Person person;
  const PersonPhoneView(this.person, {Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return TextButton(
      onPressed: () {
        open('tel://${person.phoneNumber}');
      },
      child: Text(
        '🤙🏻 Call me',
        style: TextStyle(fontSize: 20.0),
      ),
    );
  }
}

class PersonWebsiteView extends StatelessWidget {
  final Person person;
  const PersonWebsiteView(this.person, {Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return TextButton(
      onPressed: () {
        open(person.websiteUrl);
      },
      child: Text(
        '🌍 Visit my website',
        style: TextStyle(fontSize: 20.0),
      ),
    );
  }
}

const bigText = TextStyle(fontSize: 20.0);

class PersonView extends StatelessWidget {
  final Person person;
  const PersonView({Key? key, required this.person}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      decoration: BoxDecoration(
          color: Colors.blue[50],
          borderRadius: BorderRadius.circular(16.0),
          border: Border.all(color: Colors.white, width: 3.0),
          boxShadow: [
            BoxShadow(
              blurRadius: 30.0,
              color: Colors.black.withAlpha(50),
              spreadRadius: 20.0,
            ),
          ]),
      child: Padding(
        padding: const EdgeInsets.all(16.0),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            CircleAvatar(
              radius: 100.0,
              backgroundImage: NetworkImage(person.profileUrl),
            ),
            SizedBox(height: 10),
            PersonNameView(person),
            PersonEmailView(person),
            PersonPhoneView(person),
            PersonWebsiteView(person)
          ],
        ),
      ),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: SingleChildScrollView(
          child: PersonView(
            person: Person.vandad(),
          ),
        ),
      ),
    );
  }
}

Commodore 64 Screen in Flutter



import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

const textColor = Color.fromRGBO(156, 156, 247, 1);

class BoxPainter extends CustomPainter {
  final bool isBlinking;
  BoxPainter({required this.isBlinking});

  @override
  void paint(Canvas canvas, Size size) {
    if (isBlinking) {
      final rect = Rect.fromLTWH(
        size.width / 20.0,
        size.height / 2.8,
        size.width / 24.0,
        size.height / 13.0,
      );
      final paint = Paint()..color = textColor;
      canvas.drawRect(rect, paint);
    }
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => true;
}

class ReadyPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final textStyle = TextStyle(
      color: textColor,
      fontSize: size.width / 45.0,
      fontFamily: 'C64',
    );
    final span = TextSpan(
      text: 'READY',
      style: textStyle,
    );
    final painter = TextPainter(
      text: span,
      textDirection: TextDirection.ltr,
    );

    painter.layout(
      minWidth: 0,
      maxWidth: size.width,
    );
    final offset = Offset(
      painter.width / 2.0,
      painter.height * 8.0,
    );
    painter.paint(canvas, offset);
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => false;
}

class SubTitlePainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final textStyle = TextStyle(
      color: textColor,
      fontSize: size.width / 45.0,
      fontFamily: 'C64',
    );
    final span = TextSpan(
      text: '64K RAM SYSTEM 38911 BASIC BYTES FREE',
      style: textStyle,
    );
    final painter = TextPainter(
      text: span,
      textDirection: TextDirection.ltr,
    );

    painter.layout(
      minWidth: 0,
      maxWidth: size.width,
    );
    final offset = Offset(
      size.width - painter.width - (size.width / 11),
      painter.height * 6.0,
    );
    painter.paint(canvas, offset);
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => false;
}

class TitlePainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final textStyle = TextStyle(
      color: textColor,
      fontSize: size.width / 40.0,
      fontFamily: 'C64',
    );
    final span = TextSpan(
      text: '**** COMMODORE 64 BASIC V2 ****',
      style: textStyle,
    );
    final painter = TextPainter(
      text: span,
      textDirection: TextDirection.ltr,
    );

    painter.layout(
      minWidth: 0,
      maxWidth: size.width,
    );
    final offset = Offset(
      size.width - painter.width - (size.width / 9),
      size.height / 6,
    );
    painter.paint(canvas, offset);
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => false;
}

class BackgroundPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final border = size.width / 20.0;

    final color = Color.fromRGBO(
      58,
      57,
      213,
      1,
    );

    final paint = Paint()..color = color;

    final rect = Rect.fromLTWH(
      border,
      border,
      size.width - (border * 2.0),
      size.height - (border * 2.0),
    );

    canvas.drawRect(rect, paint);
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => false;
}

class BorderPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final paint = Paint()..color = textColor;
    final rect = Rect.fromLTWH(
      0.0,
      0.0,
      size.width,
      size.height,
    );

    canvas.drawRect(rect, paint);
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => false;
}

class Commodore64Painter extends CustomPainter {
  final bool isBlinking;

  late final List<CustomPainter> painters;

  Commodore64Painter({required this.isBlinking}) {
    painters = [
      BorderPainter(),
      BackgroundPainter(),
      TitlePainter(),
      SubTitlePainter(),
      ReadyPainter(),
      BoxPainter(isBlinking: isBlinking)
    ];
  }

  @override
  void paint(Canvas canvas, Size size) {
    painters.forEach(
      (p) => p.paint(
        canvas,
        size,
      ),
    );
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => painters
      .map((p) => p.shouldRepaint(oldDelegate))
      .reduce((p1, p2) => p1 || p2);
}

class Commodore64 extends StatefulWidget {
  const Commodore64({Key? key}) : super(key: key);

  @override
  State<Commodore64> createState() => _Commodore64State();
}

class _Commodore64State extends State<Commodore64> {
  bool _isBlinking = false;

  final timer = Stream.periodic(Duration(seconds: 1), (value) => value);

  void _triggerRedraw() async {
    await for (final _ in timer) {
      setState(() {
        _isBlinking = !_isBlinking;
      });
    }
  }

  @override
  void initState() {
    super.initState();
    _triggerRedraw();
  }

  @override
  Widget build(BuildContext context) {
    return LayoutBuilder(builder: (context, constraints) {
      return Container(
        width: constraints.maxWidth,
        height: constraints.maxWidth / (16.0 / 9.0),
        child: CustomPaint(
          painter: Commodore64Painter(isBlinking: _isBlinking),
        ),
      );
    });
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Commodore64(),
      ),
    );
  }
}

Animated Lists in Flutter



import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

class NetworkImage extends StatelessWidget {
  final String url;
  const NetworkImage({
    Key? key,
    required this.url,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Image.network(
      url,
      loadingBuilder: (context, child, loadingProgress) {
        final totalBytes = loadingProgress?.expectedTotalBytes;
        final bytesLoaded = loadingProgress?.cumulativeBytesLoaded;
        if (totalBytes != null && bytesLoaded != null) {
          return LinearProgressIndicator(
            value: bytesLoaded / totalBytes,
          );
        } else {
          return child;
        }
      },
      errorBuilder: (context, error, stackTrace) {
        return Text('Error!');
      },
    );
  }
}

class NetworkImageCard extends StatelessWidget {
  final String url;
  const NetworkImageCard({
    Key? key,
    required this.url,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Container(
        clipBehavior: Clip.antiAlias,
        decoration: BoxDecoration(
          borderRadius: BorderRadius.circular(20.0),
        ),
        child: NetworkImage(
          url: url,
        ),
      ),
    );
  }
}

const imageUrls = [
  'https://bit.ly/3x7J5Qt',
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3qYOtDm',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3yvFg7X',
  'https://bit.ly/3ywzOla',
  'https://bit.ly/3wnASpW',
  'https://bit.ly/3jXSDto',
];

Stream<String> images() => Stream.periodic(
      Duration(seconds: 3),
      (index) => index % imageUrls.length,
    ).map((index) => imageUrls[index]);

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  final GlobalKey<AnimatedListState> _key = GlobalKey();

  List<String> imageUrls = [];

  void populateList() async {
    await for (final url in images()) {
      imageUrls.insert(0, url);
      _key.currentState?.insertItem(
        0,
        duration: Duration(milliseconds: 400),
      );
    }
  }

  @override
  Widget build(BuildContext context) {
    populateList();
    return Scaffold(
      appBar: AppBar(
        title: Text('Animated Lists in Flutter'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(8.0),
        child: AnimatedList(
          key: _key,
          initialItemCount: imageUrls.length,
          itemBuilder: (context, index, animation) {
            final imageUrl = imageUrls[index];
            return SizeTransition(
              sizeFactor: animation.drive(
                CurveTween(curve: Curves.elasticInOut),
              ),
              child: Column(
                children: [
                  NetworkImageCard(url: imageUrl),
                  SizedBox(height: 10.0),
                ],
              ),
            );
          },
        ),
      ),
    );
  }
}

CheckboxListTile in Flutter

import 'package:flutter/material.dart';



enum Item { umbrella, coat, boots }

extension Info on Item {
  String get title {
    switch (this) {
      case Item.umbrella:
        return 'Umbrella';
      case Item.boots:
        return 'Boots';
      case Item.coat:
        return 'Jacket';
    }
  }

  String get icon {
    switch (this) {
      case Item.umbrella:
        return '☂️';
      case Item.boots:
        return '🥾';
      case Item.coat:
        return '🧥';
    }
  }
}

typedef OnChecked = void Function(bool);

class Tile extends StatelessWidget {
  final Item item;
  final bool isChecked;
  final OnChecked onChecked;
  const Tile({
    Key? key,
    required this.item,
    required this.isChecked,
    required this.onChecked,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return ConstrainedBox(
      constraints: BoxConstraints(minHeight: 100.0),
      child: Center(
        child: CheckboxListTile(
          shape: ContinuousRectangleBorder(),
          value: isChecked,
          secondary: Text(
            item.icon,
            style: TextStyle(fontSize: 30.0),
          ),
          title: Text(
            item.title,
            style: TextStyle(fontSize: 40.0),
          ),
          onChanged: (value) {
            onChecked(value ?? false);
          },
        ),
      ),
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  final Set<Item> _enabledItems = {};

  Widget get listView {
    return ListView.builder(
      shrinkWrap: true,
      itemBuilder: (context, index) {
        final item = Item.values[index];
        final isChecked = _enabledItems.contains(item);
        return Tile(
          isChecked: isChecked,
          item: item,
          onChecked: (isChecked) {
            setState(() {
              if (isChecked) {
                _enabledItems.add(item);
              } else {
                _enabledItems.remove(item);
              }
            });
          },
        );
      },
      itemCount: Item.values.length,
    );
  }

  Widget get title {
    return Padding(
      padding: const EdgeInsets.all(8.0),
      child: Text(
        "Remember to pick all items! It's going to be rainy today!",
        textAlign: TextAlign.center,
        style: TextStyle(fontSize: 40),
      ),
    );
  }

  Widget get readyButton {
    final onPressed = () async {
      // program this
      await showDialog(
        context: context,
        builder: (context) {
          return AlertDialog(
            content: Text('You seem to be ready for a rainy day! ✅'),
            actions: [
              TextButton(
                onPressed: () {
                  Navigator.of(context).pop();
                },
                child: Text('OK'),
              )
            ],
          );
        },
      );
    };

    final isEnabled = _enabledItems.containsAll(Item.values);

    return FractionallySizedBox(
      widthFactor: 0.8,
      child: ElevatedButton(
        onPressed: isEnabled ? onPressed : null,
        child: Text('Ready!'),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Checkbox List Tile in Flutter'),
      ),
      body: SingleChildScrollView(
        child: Column(
          children: [
            title,
            listView,
            SizedBox(height: 50.0),
            readyButton,
          ],
        ),
      ),
    );
  }
}

- Operator on String in Dart



extension Minus on String {
  String operator -(String rhs) => replaceAll(rhs, '');
}

void testIt() {
  assert('foo bar' - 'foo ' == 'bar');
  assert('foo bar foo' - 'foo' == ' bar ');
  assert('bar' - 'foo' == 'bar');
  assert('BAR' - 'bar' == 'BAR');
  assert('foo' - 'FOO' == 'foo');
  assert('foobarbaz' - 'bar' == 'foobaz');
}

Dart Progress for Future<T>



import 'dart:io' show stdout;
import 'dart:async' show Future, Stream;

const loadingSequence = ['⢿', '⣻', '⣽', '⣾', '⣷', '⣯', '⣟', '⡿'];
const escape = '\x1B[38;5;';
const color = '${escape}1m';
const textColor = '${escape}6m';

String progress({required int value, required String text}) {
  final progress = '$color${loadingSequence[value % loadingSequence.length]}';
  final coloredText = '$textColor$text';
  return '$progress\t$coloredText';
}

Future<T> performWithProgress<T>({
  required Future<T> task,
  required String progressText,
}) {
  final stream = Stream<String>.periodic(
    Duration(milliseconds: 100),
    (value) => progress(
      value: value,
      text: progressText,
    ),
  );

  final subscription = stream.listen(
    (event) {
      stdout.write('\r $event');
    },
  );

  task.whenComplete(() {
    stdout.write('\r ✅\t$progressText');
    stdout.write('\n');
    subscription.cancel();
  });

  return task;
}

final task1 = Future.delayed(Duration(seconds: 1), () => 'Result 1');
final task2 = Future.delayed(Duration(seconds: 2), () => 'Result 2');
final task3 = Future.delayed(Duration(seconds: 3), () => 'Result 3');

void main(List<String> args) async {
  var result = await performWithProgress(
    task: task1,
    progressText: 'Loading task 1',
  );
  print('\tTask 1 result: $result');
  result = await performWithProgress(
    task: task2,
    progressText: 'Loading task 2',
  );
  print('\tTask 2 result: $result');
  result = await performWithProgress(
    task: task3,
    progressText: 'Loading task 3',
  );
  print('\tTask 3 result: $result');
}

Move Widget Shadows with Animation



import 'package:flutter/material.dart';

class ImageTransition extends AnimatedWidget {
  final String imageUrl;

  Animation<double> get shadowXOffset => listenable as Animation<double>;

  const ImageTransition(this.imageUrl, {shadowXOffset})
      : super(listenable: shadowXOffset);

  @override
  Widget build(BuildContext context) {
    return Container(
      clipBehavior: Clip.antiAlias,
      decoration: BoxDecoration(
        borderRadius: BorderRadius.circular(20.0),
        boxShadow: [
          BoxShadow(
            blurRadius: 10,
            offset: Offset(shadowXOffset.value, 20.0),
            color: Colors.black.withAlpha(100),
            spreadRadius: -10,
          )
        ],
      ),
      child: Image.network(imageUrl),
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class CustomCurve extends CurveTween {
  CustomCurve() : super(curve: Curves.easeInOutSine);
  @override
  double transform(double t) {
    return (super.transform(t) - 0.5) * 25.0;
  }
}

class _HomePageState extends State<HomePage>
    with SingleTickerProviderStateMixin {
  late final AnimationController _controller;
  late final Animation<double> _animation;

  @override
  void initState() {
    _controller = AnimationController(
      vsync: this,
      duration: Duration(seconds: 1),
    );
    _animation = CustomCurve().animate(_controller);
    super.initState();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    _controller.repeat(reverse: true);
    return Scaffold(
      body: Padding(
        padding: const EdgeInsets.all(8.0),
        child: Center(
          child: ImageTransition(
            'https://bit.ly/3x7J5Qt',
            shadowXOffset: _animation,
          ),
        ),
      ),
    );
  }
}

Gallery with Blurred Backgrounds in Flutter


import 'package:flutter/material.dart';

const images = [
  'https://bit.ly/3x7J5Qt',
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3qYOtDm',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3yvFg7X',
  'https://bit.ly/3ywzOla',
  'https://bit.ly/3wnASpW',
  'https://bit.ly/3jXSDto',
];

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: PageView.builder(
        scrollDirection: Axis.horizontal,
        itemCount: images.length,
        itemBuilder: (context, index) {
          return WithBlurredBackground(imageUrl: images[index]);
        },
      ),
    );
  }
}

class WithBlurredBackground extends StatelessWidget {
  final String imageUrl;

  const WithBlurredBackground({Key? key, required this.imageUrl})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SizedBox.expand(
      child: Stack(
        alignment: Alignment.center,
        fit: StackFit.passthrough,
        children: [
          SizedBox.expand(
            child: ClipRect(
              child: ImageFiltered(
                imageFilter: ImageFilter.blur(
                  sigmaX: 10.0,
                  sigmaY: 10.0,
                ),
                child: Image.network(
                  imageUrl,
                  fit: BoxFit.fitHeight,
                ),
              ),
            ),
          ),
          Image.network(imageUrl),
        ],
      ),
    );
  }
}

Custom Path Clippers in Flutter



import 'package:flutter/material.dart';

const images = [
  'https://bit.ly/3x7J5Qt',
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3qYOtDm',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3yvFg7X',
  'https://bit.ly/3ywzOla',
  'https://bit.ly/3wnASpW',
  'https://bit.ly/3jXSDto',
];

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SingleChildScrollView(
        child: Padding(
          padding: const EdgeInsets.only(
            top: 40.0,
            left: 10.0,
            right: 10.0,
          ),
          child: Column(
            children: images
                .map((url) => ElevatedNetworkImage(url: url))
                .expand(
                  (img) => [
                    img,
                    SizedBox(height: 30.0),
                  ],
                )
                .toList(),
          ),
        ),
      ),
    );
  }
}

class ElevatedNetworkImage extends StatelessWidget {
  final String url;
  const ElevatedNetworkImage({Key? key, required this.url}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return PhysicalShape(
      color: Colors.white,
      clipper: Clipper(),
      elevation: 20.0,
      clipBehavior: Clip.none,
      shadowColor: Colors.white.withAlpha(200),
      child: CutEdges(
        child: Image.network(url),
      ),
    );
  }
}

class Clipper extends CustomClipper<Path> {
  static const variance = 0.2;
  static const reverse = 1.0 - variance;

  @override
  Path getClip(Size size) {
    final path = Path();

    path.moveTo(0.0, size.height * Clipper.variance);
    path.lineTo(size.width * Clipper.variance, 0.0);
    path.lineTo(size.width, 0.0);
    path.lineTo(size.width, size.height * Clipper.reverse);
    path.lineTo(size.width * Clipper.reverse, size.height);
    path.lineTo(0.0, size.height);
    path.lineTo(0.0, size.height * Clipper.variance);
    path.close;
    return path;
  }

  @override
  bool shouldReclip(covariant CustomClipper<Path> oldClipper) => false;
}

class CutEdges extends StatelessWidget {
  final Widget child;

  const CutEdges({Key? key, required this.child}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return ClipPath(
      clipper: Clipper(),
      child: child,
    );
  }
}

Frost Effect on Images in Flutter



import 'package:flutter/material.dart';

const images = [
  'https://bit.ly/3x7J5Qt',
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3qYOtDm',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3yvFg7X',
  'https://bit.ly/3ywzOla',
  'https://bit.ly/3wnASpW',
  'https://bit.ly/3jXSDto',
];

final loremIpsum =
    'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.';

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Padding(
          padding: const EdgeInsets.fromLTRB(
            8.0,
            0.0,
            8.0,
            0.0,
          ),
          child: SingleChildScrollView(
            child: Column(
              children: images
                  .map(
                    (url) => GlossyNetworkImageWithProgress(
                      url: url,
                      title: 'Image title',
                      description: loremIpsum,
                    ),
                  )
                  .expand(
                    (image) => [
                      image,
                      SizedBox(height: 16.0),
                    ],
                  )
                  .toList(),
            ),
          ),
        ),
      ),
    );
  }
}

class GlossyNetworkImageWithProgress extends StatefulWidget {
  final String url;
  final String title;
  final String description;

  const GlossyNetworkImageWithProgress(
      {Key? key,
      required this.url,
      required this.title,
      required this.description})
      : super(key: key);

  @override
  _GlossyNetworkImageWithProgressState createState() =>
      _GlossyNetworkImageWithProgressState();
}

class _GlossyNetworkImageWithProgressState
    extends State<GlossyNetworkImageWithProgress>
    with SingleTickerProviderStateMixin {
  late final AnimationController _controller;
  late final Animation<double> _animation;

  @override
  void initState() {
    super.initState();

    _controller = AnimationController(
      vsync: this,
      duration: Duration(seconds: 1),
    );

    _animation = Tween(
      begin: 0.0,
      end: 1.0,
    ).animate(_controller);
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final networkImage = Image.network(
      widget.url,
      fit: BoxFit.fitHeight,
      frameBuilder: (context, child, frame, wasSynchronouslyLoaded) {
        _controller.reset();
        _controller.forward();
        return FadeTransition(
          opacity: _animation,
          child: CustomBox(
            child: child,
          ),
        );
      },
      loadingBuilder: (context, child, loadingProgress) {
        final totalBytes = loadingProgress?.expectedTotalBytes;
        final bytesLoaded = loadingProgress?.cumulativeBytesLoaded;
        if (totalBytes != null && bytesLoaded != null) {
          return CustomBox(
            child: CircularProgressIndicator(
              backgroundColor: Colors.white70,
              value: bytesLoaded / totalBytes,
              color: Colors.blue[900],
              strokeWidth: 5.0,
            ),
          );
        } else {
          return child;
        }
      },
      errorBuilder: (context, error, stackTrace) {
        return Text('Error!');
      },
    );

    return BottomGloss(
      networkImage: networkImage,
      title: widget.title,
      description: widget.description,
    );
  }
}

class BottomGloss extends StatelessWidget {
  final String title;
  final String description;

  const BottomGloss(
      {Key? key,
      required this.networkImage,
      required this.title,
      required this.description})
      : super(key: key);

  final Image networkImage;

  @override
  Widget build(BuildContext context) {
    return ClipRRect(
      borderRadius: BorderRadius.all(Radius.circular(8.0)),
      child: Stack(
        fit: StackFit.passthrough,
        children: [
          networkImage,
          Container(
            height: 300.0,
            alignment: Alignment.bottomCenter,
            child: ClipRect(
              child: FractionallySizedBox(
                heightFactor: 0.5,
                child: BackdropFilter(
                  filter: ImageFilter.blur(
                    sigmaX: 10.0,
                    sigmaY: 10.0,
                  ),
                  child: BottomContents(
                    title: title,
                    description: description,
                  ),
                ),
              ),
            ),
          ),
        ],
      ),
    );
  }
}

class BottomContents extends StatelessWidget {
  final String title;
  final String description;

  const BottomContents({
    Key? key,
    required this.title,
    required this.description,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.white.withOpacity(0.4),
      child: Padding(
        padding: const EdgeInsets.all(8.0),
        child: SingleChildScrollView(
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: [
              TitleText(text: title),
              SizedBox(height: 8.0),
              SubTitleText(text: description),
            ],
          ),
        ),
      ),
    );
  }
}

class SubTitleText extends StatelessWidget {
  final String text;
  const SubTitleText({Key? key, required this.text}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Text(
      text,
      style: TextStyle(
        color: Colors.black,
        fontSize: 20.0,
      ),
    );
  }
}

class TitleText extends StatelessWidget {
  final String text;
  const TitleText({Key? key, required this.text}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Text(
      text,
      style: TextStyle(
        color: Colors.white,
        fontSize: 30.0,
      ),
    );
  }
}

class CustomBox extends StatelessWidget {
  final Widget child;

  const CustomBox({Key? key, required this.child}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SizedBox(
      height: 300.0,
      width: MediaQuery.of(context).size.width,
      child: child is ProgressIndicator ? Center(child: child) : child,
    );
  }
}

Custom Clippers in Flutter

import 'package:flutter/material.dart';
import 'dart:math' show min;

const gridImages = [
  'https://bit.ly/3x7J5Qt',
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/3jRSRCu',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3qYOtDm',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3yvFg7X',
  'https://bit.ly/3ywzOla',
  'https://bit.ly/3wnASpW',
  'https://bit.ly/3jXSDto',
];

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: GridView.count(
        padding: const EdgeInsets.fromLTRB(8.0, 48.0, 8.0, 48.0),
        crossAxisCount: 2,
        mainAxisSpacing: 8.0,
        crossAxisSpacing: 8.0,
        children: gridImages
            .map((url) => NetworkImageWithProgress(url: url))
            .toList(),
      ),
    );
  }
}

class CircularClipper extends CustomClipper<Rect> {
  @override
  Rect getClip(Size size) {
    final center = Offset(
      size.width / 2.0,
      size.height / 2.0,
    );
    final minWidthorHeight = min(size.width, size.height);
    return Rect.fromCenter(
      center: center,
      width: minWidthorHeight,
      height: minWidthorHeight,
    );
  }

  @override
  bool shouldReclip(covariant CustomClipper<Rect> oldClipper) => false;
}

class Circular extends StatelessWidget {
  final Widget child;
  const Circular({Key? key, required this.child}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return ClipOval(
      clipper: CircularClipper(),
      child: child,
    );
  }
}

class CustomBox extends StatelessWidget {
  final Widget child;

  const CustomBox({Key? key, required this.child}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SizedBox(
      height: 220.0,
      width: MediaQuery.of(context).size.width,
      child: child is ProgressIndicator
          ? Center(child: child)
          : Circular(child: child),
    );
  }
}

class NetworkImageWithProgress extends StatefulWidget {
  final String url;

  const NetworkImageWithProgress({Key? key, required this.url})
      : super(key: key);

  @override
  _NetworkImageWithProgressState createState() =>
      _NetworkImageWithProgressState();
}

class _NetworkImageWithProgressState extends State<NetworkImageWithProgress>
    with SingleTickerProviderStateMixin {
  late final AnimationController _controller;
  late final Animation<double> _animation;

  @override
  void initState() {
    super.initState();

    _controller = AnimationController(
      vsync: this,
      duration: Duration(seconds: 1),
    );

    _animation = Tween(
      begin: 0.0,
      end: 1.0,
    ).animate(_controller);
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Image.network(
      widget.url,
      fit: BoxFit.fitHeight,
      frameBuilder: (context, child, frame, wasSynchronouslyLoaded) {
        _controller.reset();
        _controller.forward();
        return FadeTransition(
          opacity: _animation,
          child: CustomBox(
            child: child,
          ),
        );
      },
      loadingBuilder: (context, child, loadingProgress) {
        final totalBytes = loadingProgress?.expectedTotalBytes;
        final bytesLoaded = loadingProgress?.cumulativeBytesLoaded;
        if (totalBytes != null && bytesLoaded != null) {
          return CustomBox(
            child: CircularProgressIndicator(
              backgroundColor: Colors.white70,
              value: bytesLoaded / totalBytes,
              color: Colors.blue[900],
              strokeWidth: 5.0,
            ),
          );
        } else {
          return child;
        }
      },
      errorBuilder: (context, error, stackTrace) {
        return Text('Error!');
      },
    );
  }
}

Check if Website is Up or Down in Dart



class UpStatus {
  final bool isUp;
  final DateTime timestamp;
  const UpStatus(this.isUp, this.timestamp);
}

class Pling {
  final String url;
  final Duration interval;
  const Pling({
    required this.url,
    required this.interval,
  });
  Stream<UpStatus> checkIfUp() =>
      Stream.periodic(interval, (_) => DateTime.now()).asyncExpand(
        (now) => HttpClient()
            .headUrl(Uri.parse(url))
            .then((req) => req..followRedirects = false)
            .then((req) => req.close())
            .then((resp) => resp.statusCode)
            .then((statusCode) => statusCode == 200)
            .onError((error, stackTrace) => false)
            .then((isUp) => UpStatus(isUp, now))
            .asStream(),
      );
}

const oneSecond = Duration(seconds: 1);
const url = 'https://dart.dev';

extension IsOrIsNot on bool {
  String get isOrIsNot => this ? 'is' : 'is not';
}

void testIt() async {
  final pling = Pling(
    url: url,
    interval: oneSecond,
  );
  await for (final upStatus in pling.checkIfUp()) {
    final timestamp = upStatus.timestamp;
    final isUpStr = upStatus.isUp.isOrIsNot;
    print('$url $isUpStr up at $timestamp');
  }
}

Section Titles on ListView in Flutter

import 'package:flutter/material.dart';

final List<Section> allSections = [
  Section(
    'Spring',
    [
      'https://cnn.it/3xu58Ap',
      'https://bit.ly/3ueqqC1',
    ],
  ),
  Section(
    'Summer',
    [
      'https://bit.ly/3ojNhLc',
      'https://bit.ly/2VcCSow',
    ],
  ),
  Section(
    'Autumn',
    [
      'https://bit.ly/3ib1TJk',
      'https://bit.ly/2XSpjvq',
    ],
  ),
  Section(
    'Winter',
    [
      'https://bit.ly/3iaQNE7',
      'https://bit.ly/3AY8YE4',
    ],
  ),
];

class Section {
  final String title;
  final List<String> urls;
  const Section(this.title, this.urls);
}

extension ToWidgets on Section {
  Iterable<Widget> toNetworkImageCards() {
    return [
      Padding(
        padding: const EdgeInsets.all(8.0),
        child: Text(
          title,
          style: TextStyle(
            fontSize: 40,
          ),
        ),
      ),
      ...urls.expand(
        (url) => [
          NetworkImageCard(url: url),
          SizedBox(height: 10),
        ],
      ),
    ];
  }
}

class NetworkImageCard extends StatelessWidget {
  final String url;
  const NetworkImageCard({
    Key? key,
    required this.url,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Container(
        child: NetworkImageWithProgress(
          url: url,
        ),
      ),
    );
  }
}

class NetworkImageWithProgress extends StatefulWidget {
  final String url;

  const NetworkImageWithProgress({Key? key, required this.url})
      : super(key: key);

  @override
  _NetworkImageWithProgressState createState() =>
      _NetworkImageWithProgressState();
}

class _NetworkImageWithProgressState extends State<NetworkImageWithProgress>
    with SingleTickerProviderStateMixin {
  late final AnimationController _controller;
  late final Animation<double> _animation;

  @override
  void initState() {
    super.initState();

    _controller = AnimationController(
      vsync: this,
      duration: Duration(seconds: 1),
    );

    _animation = Tween(
      begin: 0.0,
      end: 1.0,
    ).animate(_controller);
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Image.network(
      widget.url,
      fit: BoxFit.fitWidth,
      frameBuilder: (context, child, frame, wasSynchronouslyLoaded) {
        _controller.reset();
        _controller.forward();
        return FadeTransition(
          opacity: _animation,
          child: CustomBox(
            child: child,
          ),
        );
      },
      loadingBuilder: (context, child, loadingProgress) {
        final totalBytes = loadingProgress?.expectedTotalBytes;
        final bytesLoaded = loadingProgress?.cumulativeBytesLoaded;
        if (totalBytes != null && bytesLoaded != null) {
          return CustomBox(
            child: CircularProgressIndicator(
              backgroundColor: Colors.white70,
              value: bytesLoaded / totalBytes,
              color: Colors.blue[900],
              strokeWidth: 5.0,
            ),
          );
        } else {
          return child;
        }
      },
      errorBuilder: (context, error, stackTrace) {
        return Text('Error!');
      },
    );
  }
}

class CustomBox extends StatelessWidget {
  final Widget child;

  const CustomBox({Key? key, required this.child}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SizedBox(
      height: 220.0,
      width: MediaQuery.of(context).size.width,
      child: child is ProgressIndicator ? Center(child: child) : child,
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ListView.builder(
        itemBuilder: (context, index) {
          final section = allSections[index];
          return Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: section.toNetworkImageCards().toList(),
          );
        },
        itemCount: allSections.length,
      ),
    );
  }
}

Circular Progress in Flutter



import 'package:flutter/material.dart';

class CustomBox extends StatelessWidget {
  final Widget child;

  const CustomBox({Key? key, required this.child}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SizedBox(
      height: 220.0,
      width: MediaQuery.of(context).size.width,
      child: Center(child: child),
    );
  }
}

class NetworkImageWithProgress extends StatefulWidget {
  final String url;

  const NetworkImageWithProgress({Key? key, required this.url})
      : super(key: key);

  @override
  _NetworkImageWithProgressState createState() =>
      _NetworkImageWithProgressState();
}

class _NetworkImageWithProgressState extends State<NetworkImageWithProgress>
    with SingleTickerProviderStateMixin {
  late final AnimationController _controller;
  late final Animation<double> _animation;

  @override
  void initState() {
    super.initState();

    _controller = AnimationController(
      vsync: this,
      duration: Duration(seconds: 1),
    );

    _animation = Tween(
      begin: 0.0,
      end: 1.0,
    ).animate(_controller);
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Image.network(
      widget.url,
      fit: BoxFit.fitWidth,
      frameBuilder: (context, child, frame, wasSynchronouslyLoaded) {
        _controller.reset();
        _controller.forward();
        return FadeTransition(
          opacity: _animation,
          child: CustomBox(
            child: child,
          ),
        );
      },
      loadingBuilder: (context, child, loadingProgress) {
        final totalBytes = loadingProgress?.expectedTotalBytes;
        final bytesLoaded = loadingProgress?.cumulativeBytesLoaded;
        if (totalBytes != null && bytesLoaded != null) {
          return CustomBox(
            child: CircularProgressIndicator(
              backgroundColor: Colors.white70,
              value: bytesLoaded / totalBytes,
              color: Colors.blue[900],
              strokeWidth: 5.0,
            ),
          );
        } else {
          return child;
        }
      },
      errorBuilder: (context, error, stackTrace) {
        return Text('Error!');
      },
    );
  }
}

final images = [
  'https://bit.ly/3x7J5Qt',
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3ywzOla',
].map((url) => NetworkImageWithProgress(url: url)).expand(
      (element) => [
        element,
        SizedBox(
          height: 10.0,
        )
      ],
    );

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SingleChildScrollView(
        child: Column(
          children: images.toList(),
        ),
      ),
    );
  }
}

Displaying Scroll Wheels in Flutter



import 'package:flutter/material.dart';

class FadingNetworkImage extends StatefulWidget {
  final String url;

  const FadingNetworkImage({Key? key, required this.url}) : super(key: key);

  @override
  _FadingNetworkImageState createState() => _FadingNetworkImageState();
}

class _FadingNetworkImageState extends State<FadingNetworkImage>
    with SingleTickerProviderStateMixin {
  late final AnimationController _controller;
  late final Animation<double> _animation;

  @override
  void initState() {
    super.initState();

    _controller =
        AnimationController(vsync: this, duration: Duration(seconds: 1));

    _animation = Tween(begin: 0.0, end: 1.0).animate(_controller);
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Image.network(
      widget.url,
      frameBuilder: (context, child, frame, wasSynchronouslyLoaded) {
        _controller.reset();
        _controller.forward();
        return FadeTransition(
          opacity: _animation,
          child: child,
        );
      },
      loadingBuilder: (context, child, loadingProgress) {
        final totalBytes = loadingProgress?.expectedTotalBytes;
        final bytesLoaded = loadingProgress?.cumulativeBytesLoaded;
        if (totalBytes != null && bytesLoaded != null) {
          return LinearProgressIndicator(
            value: bytesLoaded / totalBytes,
          );
        } else {
          return child;
        }
      },
      errorBuilder: (context, error, stackTrace) {
        return Text('Error!');
      },
    );
  }
}

final images = [
  'https://bit.ly/3x7J5Qt',
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3ywzOla',
].map((i) => NetworkImageCard(url: i));

class NetworkImageCard extends StatelessWidget {
  final String url;
  const NetworkImageCard({
    Key? key,
    required this.url,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Container(
        clipBehavior: Clip.antiAlias,
        decoration: BoxDecoration(
          borderRadius: BorderRadius.circular(20.0),
          boxShadow: [
            BoxShadow(
              blurRadius: 5,
              offset: Offset(0, 0),
              color: Colors.black.withAlpha(40),
              spreadRadius: 5,
            )
          ],
        ),
        child: FadingNetworkImage(
          url: url,
        ),
      ),
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ListWheelScrollView(
        itemExtent: 164.0,
        squeeze: 0.9,
        perspective: 0.003,
        children: images.toList(),
      ),
    );
  }
}

Post Messages to Slack with Dart



import 'dart:convert' show utf8;
import 'dart:convert' show json;

class SlackMessage {
  final String? inChannel;
  final String? userName;
  final String message;
  final String? iconEmoji;

  const SlackMessage({
    required this.inChannel,
    required this.userName,
    required this.message,
    required this.iconEmoji,
  });

  Future<bool> send(String webhookUrl) async {
    final payload = {
      'text': message,
      if (inChannel != null) 'channel': inChannel!,
      if (userName != null) 'username': userName!,
      if (iconEmoji != null) 'icon_emoji': iconEmoji!
    };

    final request = await HttpClient().postUrl(Uri.parse(webhookUrl));
    final payloadData = utf8.encode(json.encode(payload));
    request.add(payloadData);
    final response = await request.close();
    return response.statusCode == 200;
  }
}

const webhookUrl = 'put your webhook url here';

void testIt() async {
  final message = SlackMessage(
    inChannel: 'dart',
    userName: 'Flutter',
    message: 'Hello from Dart in Terminal',
    iconEmoji: 'blue_heart:',
  );
  if (await message.send(webhookUrl)) {
    print('Successfully sent the message');
  } else {
    print('Could not send the message');
  }
}

Unwrap List<T?>? in Dart



extension Unwrap<T> on List<T?>? {
  List<T> unwrap() => (this ?? []).whereType<T>().toList();
}

void testOptionalListOfOptionals() {
  final List<int?>? optionalListOfOptionals = [1, 2, null, 3, null];
  final unwrapped = optionalListOfOptionals.unwrap(); // List<int>
  print(unwrapped); // prints [1, 2, 3]
}

void testListOfOptionals() {
  final listOfOptionals = [20, 30, null, 40]; // List<int?>
  final unwrapped = listOfOptionals.unwrap(); // List<int>
  print(unwrapped); // prints [20, 30, 40]
}

void testNormalList() {
  final list = [50, 60, 70]; // List<int>
  final unwrapped = list.unwrap(); // List<int>
  print(unwrapped); // prints [50, 60, 70]
}

Avoiding UI Jitters When Switching Widgets in Flutter



const imageUrls = [
  'https://cnn.it/3xu58Ap', // spring
  'https://bit.ly/2VcCSow', // summer
  'https://bit.ly/3A3zStC', // autumn
  'https://bit.ly/2TNY7wi' // winter
];

extension ToNetworkImage<T extends String> on List<T> {
  List<Widget> toNetworkImages() => map((s) => Image.network(s)).toList();
}

class HomePage extends StatefulWidget {
  @override
  State createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  var _currentIndex = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Indexed Stack')),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            IndexedStack(
              index: _currentIndex,
              children: imageUrls.toNetworkImages(),
            ),
            TextButton(
              onPressed: () {
                setState(
                  () {
                    _currentIndex++;
                    if (_currentIndex >= imageUrls.length) {
                      _currentIndex = 0;
                    }
                  },
                );
              },
              child: Text('Go to next season'),
            )
          ],
        ),
      ),
    );
  }
}

Detect Redirects in Dart



Future<bool> doesRedirect(String url) => HttpClient()
    .headUrl(Uri.parse(url))
    .then((req) => req..followRedirects = false)
    .then((req) => req.close())
    .then((resp) => resp.statusCode)
    .then((statusCode) => [301, 302, 303, 307, 308].contains(statusCode));

void testIt() async {
  final test1 = await doesRedirect('https://cnn.it/3xu58Ap');
  assert(test1 == true);

  final test2 = await doesRedirect('https://dart.dev');
  assert(test2 == false);

  final test3 = await doesRedirect('https://bit.ly/2VcCSow');
  assert(test3 == true);
}

Proportional Constraints in Flutter



class ProportionalWidthNetworkImage extends StatelessWidget {
  final String url;
  final double widthProportion;

  const ProportionalWidthNetworkImage(
      {Key? key, required this.url, required this.widthProportion})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    return LayoutBuilder(
      builder: (context, constraints) {
        return Image.network(
          url,
          loadingBuilder: (context, child, loadingProgress) {
            final widget =
                loadingProgress == null ? child : LinearProgressIndicator();
            return Container(
              width: constraints.maxWidth * widthProportion,
              child: widget,
            );
          },
        );
      },
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: ProportionalWidthNetworkImage(
          url: 'https://cnn.it/3xu58Ap',
          widthProportion: 0.8,
        ),
      ),
    );
  }
}

Displaying Cupertino Action Sheets in Flutter



import 'package:flutter/cupertino.dart';

enum Season { spring, summer, autumn, winter }

extension Title on Season {
  String get title => describeEnum(this).capitalized;
}

extension Caps on String {
  String get capitalized => this[0].toUpperCase() + substring(1);
}

extension ToWidget on Season {
  Widget toWidget() {
    switch (this) {
      case Season.spring:
        return Image.network('https://cnn.it/3xu58Ap');
      case Season.summer:
        return Image.network('https://bit.ly/2VcCSow');
      case Season.autumn:
        return Image.network('https://bit.ly/3A3zStC');
      case Season.winter:
        return Image.network('https://bit.ly/2TNY7wi');
    }
  }
}

class HomePage extends StatefulWidget {
  HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

Future<Season> _chooseSeason(
  BuildContext context,
  Season currentSeason,
) async {
  CupertinoActionSheet actionSheet(BuildContext context) {
    return CupertinoActionSheet(
      title: Text('Choose your favorite season:'),
      actions: Season.values
          .map(
            (season) => CupertinoActionSheetAction(
              onPressed: () {
                Navigator.of(context).pop(season);
              },
              child: Text(season.title),
            ),
          )
          .toList(),
      cancelButton: CupertinoActionSheetAction(
        onPressed: () {
          Navigator.of(context).pop(currentSeason);
        },
        child: Text('Cancel'),
      ),
    );
  }

  return await showCupertinoModalPopup(
    context: context,
    builder: (context) => actionSheet(context),
  );
}

class _HomePageState extends State<HomePage> {
  var _season = Season.spring;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(_season.title),
      ),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          _season.toWidget(),
          TextButton(
            onPressed: () async {
              _season = await _chooseSeason(
                context,
                _season,
              );
              setState(() {});
            },
            child: Text('Choose a season'),
          ),
        ],
      ),
    );
  }
}

Rotating List<T> in Dart



extension Rotate<T> on List<T> {
  int _rotationTimes(int places) {
    if (isEmpty) {
      return 0;
    }
    if (places == 0) {
      throw ArgumentError('places should be more than 0');
    }
    return places % length;
  }

  List<T> rotatedRight(int places) {
    final times = _rotationTimes(places);
    if (times == 0) {
      return this;
    } else {
      final cutOff = length - times;
      return sublist(cutOff)..addAll(sublist(0, cutOff));
    }
  }

  List<T> rotatedLeft(int places) {
    final times = _rotationTimes(places);
    if (times == 0) {
      return this;
    } else {
      return sublist(times)..addAll(sublist(0, times));
    }
  }
}

extension Equality<T extends Comparable> on List<T> {
  bool isEqualTo(List<T> other) {
    if (other.length != length) {
      return false;
    }
    for (var i = 0; i < length; i++) {
      if (other[i] != this[i]) {
        return false;
      }
    }
    return true;
  }
}

const arr = [1, 2, 3];

void testIt() {
  assert(arr.rotatedRight(1).isEqualTo([3, 1, 2]));
  assert(arr.rotatedRight(2).isEqualTo([2, 3, 1]));
  assert(arr.rotatedRight(3).isEqualTo([1, 2, 3]));
  assert(arr.rotatedRight(4).isEqualTo([3, 1, 2]));
  assert(arr.rotatedLeft(1).isEqualTo([2, 3, 1]));
  assert(arr.rotatedLeft(2).isEqualTo([3, 1, 2]));
  assert(arr.rotatedLeft(3).isEqualTo([1, 2, 3]));
  assert(arr.rotatedLeft(4).isEqualTo([2, 3, 1]));
}

Displaying SnackBars in Flutter



class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Hello world'),
      ),
      body: Center(
        child: TextButton(
          onPressed: () {
            final now = DateFormat('kk:mm:ss').format(DateTime.now());
            ScaffoldMessenger.of(context).removeCurrentSnackBar();
            ScaffoldMessenger.of(context).showSnackBar(
              SnackBar(
                behavior: SnackBarBehavior.floating,
                elevation: 5.0,
                backgroundColor:
                    Colors.blue[600]!.withOpacity(0.8).withAlpha(200),
                shape: RoundedRectangleBorder(
                  borderRadius: BorderRadius.circular(10),
                  side: BorderSide(
                    color: Colors.black.withOpacity(0.4),
                    width: 3.0,
                  ),
                ),
                content: Text('Some text $now'),
              ),
            );
          },
          child: Text('Show toast'),
        ),
      ),
    );
  }
}

Custom Tab Bar Using ToggleButtons in Flutter



class TabBarButton extends StatelessWidget {
  final IconData icon;
  final double size;

  const TabBarButton({Key? key, required this.icon, this.size = 60.0})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(8.0),
      child: Icon(
        icon,
        size: size,
      ),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Toggle Buttons'),
      ),
      body: Column(
        children: [
          CustomTabBar(),
        ],
      ),
    );
  }
}

class CustomTabBar extends StatefulWidget {
  const CustomTabBar({Key? key}) : super(key: key);

  @override
  _CustomTabBarState createState() => _CustomTabBarState();
}

class _CustomTabBarState extends State<CustomTabBar> {
  var _selection = [false, false, false];

  @override
  Widget build(BuildContext context) {
    return Expanded(
      child: Align(
        alignment: FractionalOffset.bottomCenter,
        child: SafeArea(
          child: ToggleButtons(
            isSelected: _selection,
            onPressed: (index) {
              setState(() {
                _selection = List.generate(
                  _selection.length,
                  (i) => index == i ? true : false,
                );
              });
            },
            selectedColor: Colors.white,
            fillColor: Colors.blue,
            borderRadius: BorderRadius.circular(10.0),
            borderWidth: 4.0,
            borderColor: Colors.blue[400],
            selectedBorderColor: Colors.blue,
            highlightColor: Colors.blue.withOpacity(0.2),
            children: [
              TabBarButton(icon: Icons.settings),
              TabBarButton(icon: Icons.add),
              TabBarButton(icon: Icons.settings_remote)
            ],
          ),
        ),
      ),
    );
  }
}

Hashable Mixins in Dart



enum PetType { cat, dog }

mixin Pet {
  String get name;
  int get age;
  PetType get type;
  @override
  String toString() => 'Pet ($type), name = $name, age = $age';
  @override
  int get hashCode => hashValues(name, age, type);
  @override
  bool operator ==(covariant Pet o) => o.hashCode == hashCode;
}

class Cat with Pet {
  @override
  final String name;
  @override
  final int age;
  @override
  final PetType type;
  const Cat({required this.name, required this.age}) : type = PetType.cat;
}

void testIt() {
  final cats = <Cat>{
    Cat(name: 'Kitty 1', age: 2),
    Cat(name: 'Kitty 2', age: 3),
    Cat(name: 'Kitty 1', age: 2),
  };
  cats.forEach(print);
  /* 👆🏻 prints the following:
  Pet (PetType.cat), name = Kitty 1, age = 2
  Pet (PetType.cat), name = Kitty 2, age = 3
  */
}

Flutter Tips and Tricks in Terminal



import 'dart:convert' show utf8;
import 'dart:io' show HttpClient, exit, Process, stderr;
import 'dart:math' show Random;

const rawBlobRoot =
    'https://raw.githubusercontent.com/vandadnp/flutter-tips-and-tricks/main/';

void main(List<String> args) async {
  final url = Uri.https('bit.ly', '/2V1GKsC');
  try {
    final client = HttpClient();
    final images = await client
        .getUrl(url)
        .then((req) => req.close())
        .then((resp) => resp.transform(utf8.decoder).join())
        .then((body) => body.split('\n').map((e) => e.trim()))
        .then((iter) => iter.toList())
        .then((list) => list..retainWhere((s) => s.endsWith('.jpg)')))
        .then((imageList) => imageList.map((e) => e.replaceAll('![](', '')))
        .then((imageList) => imageList.map((e) => e.replaceAll(')', '')))
        .then((iter) => iter.toList());

    final found = images[Random().nextInt(images.length)];
    final result = '$rawBlobRoot$found';
    await Process.run('open', [result]);
    exit(0);
  } catch (e) {
    stderr.writeln('Could not proceed due to $e');
    exit(1);
  }
}

Searching List<List<T>> in Dart



const arr1 = [1, 2, 3];
const arr2 = [4, 5, 6];
const arr3 = [7, 8, 9];
const arr = [arr1, arr2, arr3];

extension FlattenFind<T extends Comparable> on Iterable<Iterable<T>> {
  bool containsElement(T value) {
    for (final arr in this) {
      if (arr.contains(value)) {
        return true;
      }
    }
    return false;
  }
}

void testIt() {
  assert(arr.containsElement(2));
  assert(arr.containsElement(8));
  assert(!arr.containsElement(10));
  assert(!arr.containsElement(10));
}

Cloning Objects in Dart



class Person {
  final Map<String, Object> _values;
  static const FIRST_NAME_KEY = 'FIRST_NAME';
  static const LAST_NAME_KEY = 'LAST_NAME';

  Person.from(Map<String, Object> props) : _values = props;

  Person({
    required String firstName,
    required String lastName,
    Map<String, Object>? props,
  }) : _values = {
          FIRST_NAME_KEY: firstName,
          LAST_NAME_KEY: lastName,
        };

  @override
  bool operator ==(covariant Person other) =>
      other.firstName == firstName && other.lastName == lastName;

  @override
  String toString() => _values.toString();
}

extension Properties on Person {
  String get firstName => _values[Person.FIRST_NAME_KEY].toString();
  set firstName(String newValue) => _values[Person.FIRST_NAME_KEY] = newValue;

  String get lastName => _values[Person.LAST_NAME_KEY].toString();
  set lastName(String newValue) => _values[Person.LAST_NAME_KEY] = newValue;
}

extension Clone on Person {
  Person clone([Map<String, Object>? additionalProps]) =>
      Person.from(Map.from(_values)..addAll(additionalProps ?? {}));
}

extension Subscripts on Person {
  Object? operator [](String key) => _values[key];
  operator []=(String key, Object value) => _values[key] = value;
}

void testIt() {
  final foo = Person(
    firstName: 'Foo Firstname',
    lastName: 'Foo Lastname',
  );
  print(foo); // {FIRST_NAME: Foo Firstname, LAST_NAME: Foo Lastname}
  final copyOfFoo = foo.clone();
  print(copyOfFoo); // {FIRST_NAME: Foo Firstname, LAST_NAME: Foo Lastname}
  final bar = foo.clone({'age': 30});
  print(bar); // {FIRST_NAME: Foo Firstname, LAST_NAME: Foo Lastname, age: 30}
  assert(foo == copyOfFoo);
  assert(foo == bar);
  assert(foo['age'] == null);
  assert(copyOfFoo['age'] == null);
  assert(bar['age'] == 30);
}

Color Filters in Flutter



class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  var sliderValue = 0.0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Color Filters in Flutter!'),
      ),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          ColorFiltered(
            colorFilter: ColorFilter.mode(
              Colors.orange.withOpacity(sliderValue),
              BlendMode.colorBurn,
            ),
            child: Image.network('https://tinyurl.com/4vtvh35h'),
          ),
          Slider(
            value: sliderValue,
            onChanged: (value) {
              setState(() {
                sliderValue = value;
              });
            },
          )
        ],
      ),
    );
  }
}

Flattening Lists in Dart



class Person {
  final String name;
  const Person(this.name);
  @override
  String toString() => 'Person: $name';
}

class House {
  final List<Person>? tennants;
  final List<Person> builders;
  const House({
    required this.tennants,
    required this.builders,
  });
}

const houses = [
  House(tennants: null, builders: [
    Person('Builder 1'),
  ]),
  House(tennants: [
    Person('Tennant 1'),
    Person('Tennant 2'),
  ], builders: [
    Person('Builder 3')
  ]),
];

extension OptionalFlattend<T> on Iterable<List<T>?> {
  Iterable<T> flattened() => expand((e) => e ?? []);
}

void testOptionalFlatten() {
  final allTennants = houses.map((h) => h.tennants).flattened();
  print(allTennants); // Person: Tennant 1, Person: Tennant 2
}

extension Flattend<T> on Iterable<List<T>> {
  Iterable<T> flattened() => expand((e) => e);
}

void testNonOptionalFlatten() {
  final allBuilders = houses.map((h) => h.builders).flattened();
  print(allBuilders); // Person: Builder 1, Person: Builder 2
}

void testIt() {
  testOptionalFlatten();
  testNonOptionalFlatten();
}

Managing Duplicates in List<T> in Dart



extension Duplicates<T> on List<T> {
  void addAllByAvoidingDuplicates(Iterable<T> values) =>
      replaceRange(0, length, {
        ...([...this] + [...values])
      });

  int get numberOfDuplicates => length - {...this}.length;

  bool get containsDuplicates => numberOfDuplicates > 0;

  List<T> get uniques => [
        ...{...this}
      ];

  void removeDuplicates() => replaceRange(
        0,
        length,
        uniques,
      );

  List<T> get duplicates => [
        for (var i = 0; i < length; i++)
          [...this].skip(i + 1).contains(this[i]) ? this[i] : null
      ].whereType<T>().toList();
}

void testIt() {
  final values = [3, 2, 10, 30, 40, 30, 100, 10];

  assert(values.numberOfDuplicates == 2);
  assert(values.containsDuplicates == true);

  assert(values.uniques.length == values.length - 2);
  print(values.uniques); // [3, 2, 10, 30, 40, 100]

  values.removeDuplicates();
  print(values); // [3, 2, 10, 30, 40, 100]

  assert(values.numberOfDuplicates == 0);
  assert(!values.containsDuplicates);
  assert(values.duplicates.isEmpty);

  values.addAllByAvoidingDuplicates([3, 2, 10, 200]);
  print(values); // [3, 2, 10, 30, 40, 100, 200]
  assert(values.containsDuplicates == false);
}

FlatMap and CompactMap in Dart



extension CompactMap<T> on List<T> {
  List<E> compactMap<E>(E? Function(T element) f) {
    Iterable<E> imp(E? Function(T element) f) sync* {
      for (final value in this) {
        final mapped = f(value);
        if (mapped != null) {
          yield mapped;
        }
      }
    }

    return imp(f).toList();
  }
}

extension FlatMap<T> on T? {
  E? flatMap<E>(E? Function(T value) f) {
    if (this != null) {
      return f(this!);
    } else {
      return null;
    }
  }
}

void testIt() {
  final foo = [1, 2, null, 3, null, 4];
  final bar = foo.compactMap((element) => element.flatMap((e) => e * 2));
  print(bar); // prints 2, 4, 6, 8
}

Equality of List<T> in Dart



extension Equality<T extends Comparable> on List<T> {
  bool isEqualTo(List<T> other) {
    if (other.length != length) {
      return false;
    }
    for (var i = 0; i < length; i++) {
      if (other[i] != this[i]) {
        return false;
      }
    }
    return true;
  }
}

int ascendingComparator<T extends Comparable>(T lhs, T rhs) =>
    lhs.compareTo(rhs);
int descendingComparator<T extends Comparable>(T lhs, T rhs) =>
    rhs.compareTo(lhs);

extension Sorted<T extends Comparable> on List<T> {
  List<T> sorted({bool descending = false}) => descending
      ? ([...this]..sort(descendingComparator))
      : ([...this]..sort(ascendingComparator));
}

void testIt() {
  assert([1, 2, 3].isEqualTo([1, 2, 3]));
  assert(![1, 2, 3].isEqualTo([1, 2, 2]));
  assert([3, 1, 2].sorted().isEqualTo([1, 2, 3]));
  assert(![3, 1, 2].sorted().isEqualTo([3, 1, 2]));
  assert(['Foo', 'Bar', 'Baz'].isEqualTo(['Foo', 'Bar', 'Baz']));
  assert(!['Foo', 'Bar', 'Baz'].isEqualTo(['foo', 'Bar', 'Baz']));
}

Constants in Dart




class Person {
  final String name;
  final int age;
  const Person({required this.name, required this.age});
}

const foo = Person(name: 'Foo', age: 20);
const foo2 = Person(name: 'Foo', age: 20);
const bar = Person(name: 'Bar', age: 20);

void assert_eq(Object lhs, Object rhs) {
  assert(lhs == rhs);
}

void assert_ne(Object lhs, Object rhs) {
  assert(lhs != rhs);
}

void testIt() {
  assert_eq(foo, foo2);
  assert_ne(foo, bar);
  assert_ne(foo2, bar);
}

Displaying Scrollable Bottom Sheets in Flutter



class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Scrollable Sheet')),
      body: DraggableScrollableSheet(
        initialChildSize: 0.2,
        minChildSize: 0.2,
        maxChildSize: 0.8,
        builder: (context, scrollController) {
          return Container(
            decoration: decoration(),
            clipBehavior: Clip.antiAlias,
            child: SingleChildScrollView(
              controller: scrollController,
              child: column(),
            ),
          );
        },
      ),
    );
  }
}

const urls = [
  'https://tinyurl.com/4vtvh35h',
  'https://tinyurl.com/pujhs55w',
  'https://tinyurl.com/u5k7zueh',
];

List<Widget> imageWithLoremIpsum(String uri) => [
      Image.network(uri),
      SizedBox(height: 10),
      loremIpsum(),
      SizedBox(height: 10),
    ];

Column column() => Column(
      children: imageWithLoremIpsum(urls[0]) +
          imageWithLoremIpsum(urls[1]) +
          imageWithLoremIpsum(urls[2]),
    );

Text loremIpsum() => Text(
      'Lorem ipsum ' * 10,
      textAlign: TextAlign.center,
    );

BoxDecoration decoration() => BoxDecoration(
      border: Border.all(color: Colors.white),
      borderRadius: BorderRadius.only(
        topLeft: Radius.circular(10),
        topRight: Radius.circular(10),
      ),
      color: Colors.white70,
    );

YouTube Ad Remover in Dart



import 'dart:io' show stdout, stderr, exitCode;
import 'package:collection/collection.dart' show IterableExtension;

// example argument: https://www.youtube.com/watch?v=mtETXtSP0pA
void main(List<String> args) async {
  if (args.isEmpty) {
    stdout.writeln('usage: dart youtube.dart "https://..."');
    return;
  }

  final link =
      args.firstWhereOrNull((element) => Uri.tryParse(element) != null);

  if (link == null) {
    stderr.writeln('No YouTube url found');
    exitCode = 1;
    return;
  }

  try {
    final uri = Uri.parse(link);
    if (uri.scheme.toLowerCase() != 'https' ||
        uri.host.toLowerCase() != 'www.youtube.com' ||
        uri.queryParameters['v'] == null) {
      throw FormatException();
    } else {
      final videoId = uri.queryParameters['v'];
      final embedUri = Uri.parse('${uri.scheme}://${uri.host}/embed/$videoId');
      stdout.writeln(embedUri);
      exitCode = 0;
    }
  } on FormatException catch (e) {
    stderr.writeln('Invalid Uri, try again! err = $e');
    exitCode = 1;
    return;
  }
}

Fade Between Widgets in Flutter



const urls = [
  'https://bit.ly/3qYOtDm',
  'https://bit.ly/3wt11Ec',
];

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  var isShowingFirstImage = true;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('AnimatedCrossFade in Flutter'),
      ),
      body: Center(
        child: AnimatedCrossFade(
          layoutBuilder: (topChild, topChildKey, bottomChild, bottomChildKey) {
            return GestureDetector(
              onTap: () {
                setState(() {
                  isShowingFirstImage = !isShowingFirstImage;
                });
              },
              child: AnimatedCrossFade.defaultLayoutBuilder(
                  topChild, topChildKey, bottomChild, bottomChildKey),
            );
          },
          firstChild: Image.network(urls[0]),
          secondChild: Image.network(urls[1]),
          crossFadeState: isShowingFirstImage
              ? CrossFadeState.showFirst
              : CrossFadeState.showSecond,
          duration: Duration(milliseconds: 400),
        ),
      ),
    );
  }
}

Sort Descriptors in Dart



int ascendingComparator<T extends Comparable>(T lhs, T rhs) =>
    lhs.compareTo(rhs);
int descendingComparator<T extends Comparable>(T lhs, T rhs) =>
    rhs.compareTo(lhs);

extension Sorted<T extends Comparable> on List<T> {
  List<T> sorted({bool descending = false}) => descending
      ? (this..sort(descendingComparator))
      : (this..sort(ascendingComparator));
}

class Person implements Comparable {
  final int age;
  final String name;
  const Person({required this.age, required this.name});
  @override
  int compareTo(covariant Person other) => age.compareTo(other.age);
  @override
  String toString() => 'Person, name = $name ($age)';
}

void testIt() {
  final people = [
    Person(age: 39, name: 'Father Foo'),
    Person(age: 40, name: 'Mother Bar'),
    Person(age: 13, name: 'Son Baz'),
  ];

  print('ascending sort');
  people.sorted().forEach(print);
  // prints Son Baz (13), Father Foo (39), Mother Bar (40)
  print('descending sort');
  people.sorted(descending: true).forEach(print);
  // prints Mother Bar (40), Father Foo (39), Son Baz (13)
}

User Sortable Columns and Tables in Flutter



class Language {
  final String name;
  final Image image;
  const Language(this.name, this.image);
  Language.dart()
      : name = 'Dart',
        image = Image.network('https://bit.ly/3yH1Ivj');
  Language.rust()
      : name = 'Rust',
        image = Image.network('https://bit.ly/3lPTqhb');
  Language.python()
      : name = 'Python',
        image = Image.network('https://bit.ly/3iCFCEP');

  Language.java()
      : name = 'Java',
        image = Image.network('https://bit.ly/3CCapJH');
  static List<Language> all = [
    Language.dart(),
    Language.rust(),
    Language.python(),
    Language.java(),
  ];
}

extension Sort on List<Language> {
  void sortByName(bool ascending) => sort((lhs, rhs) =>
      ascending ? lhs.name.compareTo(rhs.name) : rhs.name.compareTo(lhs.name));
}

List<DataRow> rows(List<Language> langs) => langs
    .map(
      (l) => DataRow(
        cells: [
          DataCell(
            Padding(
              padding: const EdgeInsets.all(8.0),
              child: l.image,
            ),
          ),
          DataCell(Text(l.name)),
        ],
      ),
    )
    .toList();

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  final List<Language> _langs = Language.all..sortByName(true);
  int sortedColumnIndex = 1;
  var isSortedAscending = true;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('WhatsApp')),
      body: DataTable(
        sortAscending: isSortedAscending,
        sortColumnIndex: sortedColumnIndex,
        columns: [
          DataColumn(label: Text('Image')),
          DataColumn(
            label: Text('Name'),
            onSort: (columnIndex, ascending) {
              setState(() {
                sortedColumnIndex = columnIndex;
                isSortedAscending = ascending;
                _langs.sortByName(ascending);
              });
            },
          ),
        ],
        rows: rows(_langs),
      ),
    );
  }
}

Content-Length of List<Uri> in Dart

Recursive Dot Notation on Maps in Dart




final person = {
  'firstName': 'Foo',
  'lastName': 'Bar',
  'age': 30,
  'address': {
    'street': {
      'name': 'Baz street',
      'numberOfHouses': 20,
    },
    'houseNumber': '#20',
    'city': 'Stockholm',
    'country': 'Sweden'
  },
};

extension KeyPath on Map {
  Object? valueFor({required String keyPath}) {
    final keysSplit = keyPath.split('.');
    final thisKey = keysSplit.removeAt(0);
    final thisValue = this[thisKey];
    if (keysSplit.isEmpty) {
      return thisValue;
    } else if (thisValue is Map) {
      return thisValue.valueFor(keyPath: keysSplit.join('.'));
    }
  }
}

void testIt() {
  assert(person.valueFor(keyPath: 'firstName') == 'Foo');
  assert(person.valueFor(keyPath: 'age') == 30);
  assert(person.valueFor(keyPath: 'address.street.name') == 'Baz street');
  assert(person.valueFor(keyPath: 'address.houseNumber') == '#20');
}

Allow User Selection of Text in Flutter



const text = 'Flutter is an open-source UI software development'
    ' kit created by Google. It is used to develop cross platform applications'
    ' for Android, iOS, Linux, Mac, Windows, Google Fuchsia, '
    'and the web from a single codebase.';

const imageUrl = 'https://bit.ly/3gT5Qk2';

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Selectable Text in Flutter'),
      ),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Image.network(imageUrl),
          SizedBox(height: 10.0),
          Padding(
            padding: const EdgeInsets.all(8.0),
            child: SelectableText(
              text,
              textAlign: TextAlign.center,
              showCursor: true,
              cursorColor: Colors.blue,
              toolbarOptions: ToolbarOptions(
                copy: true,
                selectAll: true,
              ),
              style: TextStyle(
                fontSize: 20,
                fontWeight: FontWeight.w300,
              ),
            ),
          ),
        ],
      ),
    );
  }
}

Placing Constraints on Widgets in Flutter



const dashes = [
  'https://bit.ly/3gHlTCU',
  'https://bit.ly/3wOLO1c',
  'https://bit.ly/3cXWD9j',
  'https://bit.ly/3gT5Qk2',
];

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('ConstrainedBox in Flutter'),
      ),
      body: InteractiveViewer(
        minScale: 1.0,
        maxScale: 2.0,
        child: SingleChildScrollView(
          scrollDirection: Axis.vertical,
          child: Table(
            defaultVerticalAlignment: TableCellVerticalAlignment.middle,
            children: dashes
                .map(
                  (dash) => TableRow(
                    children: [
                      ConstrainedBox(
                        constraints: BoxConstraints(
                          minHeight: 300,
                        ),
                        child: Image.network(dash),
                      ),
                    ],
                  ),
                )
                .toList(),
          ),
        ),
      ),
    );
  }
}

Animating Position Changes in Flutter



class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  var isMovedUp = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('AnimatedPositioned in Flutter')),
      body: Center(
        child: GestureDetector(
          onTap: () => setState(() => isMovedUp = !isMovedUp),
          child: Stack(
            clipBehavior: Clip.none,
            alignment: Alignment.center,
            children: [
              Image.network('https://bit.ly/2VcCSow'),
              Text(
                'Summer 😎',
                style: TextStyle(
                  fontSize: 30,
                  color: Colors.black,
                ),
              ),
              AnimatedPositioned(
                duration: Duration(seconds: 1),
                bottom: isMovedUp ? 140 : 10.0,
                curve: Curves.elasticInOut,
                child: CircleAvatar(
                  radius: 100,
                  backgroundImage: NetworkImage('https://bit.ly/3cXWD9j'),
                  backgroundColor: Colors.orange[300],
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

Transitioning Between Widgets in Flutter



enum Season { spring, summer, autumn, winter }

extension Caps on String {
  String get capitalized => this[0].toUpperCase() + substring(1);
}

extension Title on Season {
  String get title => describeEnum(this).capitalized;
}

class TitledImage {
  final String title;
  final Uri uri;
  final ValueKey key;
  const TitledImage(this.title, this.uri, this.key);

  TitledImage.spring()
      : title = Season.spring.title,
        uri = Uri.https('cnn.it', '/3xu58Ap'),
        key = ValueKey(1);

  TitledImage.summer()
      : title = Season.summer.title,
        uri = Uri.https('bit.ly', '/2VcCSow'),
        key = ValueKey(2);

  TitledImage.autumn()
      : title = Season.autumn.title,
        uri = Uri.https('bit.ly', '/3A3zStC'),
        key = ValueKey(3);

  TitledImage.winter()
      : title = Season.winter.title,
        uri = Uri.https('bit.ly', '/2TNY7wi'),
        key = ValueKey(4);
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  var _img = TitledImage.summer();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(_img.title)),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          AnimatedSwitcher(
            switchInCurve: Curves.easeIn,
            switchOutCurve: Curves.easeOut,
            duration: Duration(milliseconds: 300),
            transitionBuilder: (child, animation) {
              return FadeTransition(opacity: animation, child: child);
            },
            child: Image.network(
              _img.uri.toString(),
              key: _img.key,
            ),
          ),
          getButtons(),
        ],
      ),
    );
  }

  Widget getButtons() {
    return Row(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        TextButton(
          onPressed: () => setState(() => _img = TitledImage.spring()),
          child: Text(Season.spring.title),
        ),
        TextButton(
          onPressed: () => setState(() => _img = TitledImage.summer()),
          child: Text(Season.summer.title),
        ),
        TextButton(
          onPressed: () => setState(() => _img = TitledImage.autumn()),
          child: Text(Season.autumn.title),
        ),
        TextButton(
          onPressed: () => setState(() => _img = TitledImage.winter()),
          child: Text(Season.winter.title),
        ),
      ],
    );
  }
}

Doubly Linked Lists in Dart



class Person extends LinkedListEntry<Person> {
  final String name;
  final int age;
  Person({
    required this.name,
    required this.age,
  });

  @override
  String toString() => 'Person name = $name, age = $age';
}

void testIt() {
  final persons = LinkedList<Person>();
  final dad = Person(name: 'Father Foo', age: 47);
  final mom = Person(name: 'Mother Bar', age: 47);
  final daughter = Person(name: 'Daughter Baz', age: 22);
  persons.addAll([dad, mom, daughter]);

  print(persons.first.previous); // null
  print(persons.first); // Person name = Father Foo, age = 47
  print(persons.first.next); // Person name = Mother Bar, age = 47
  print(persons.last.previous); // Person name = Mother Bar, age = 47
  print(persons.first.next?.next); // Person name = Daughter Baz, age = 22
  print(persons.last.next); // null
}

Reordering Items Inside List Views in Flutter



class Item {
  final Color color;
  final String text;
  final UniqueKey uniqueKey;
  Item(this.color, this.text) : uniqueKey = UniqueKey();
}

extension ToListItem on Item {
  Widget toListItem() => LimitedBox(
        key: uniqueKey,
        maxHeight: 200,
        child: Container(
          color: color,
          child: Padding(
            padding: const EdgeInsets.all(20),
            child: Text(
              text,
              style: TextStyle(
                color: Colors.white,
                fontSize: 100,
              ),
            ),
          ),
        ),
      );
}

class _HomePageState extends State<HomePage> {
  var items = [
    Item(Colors.deepPurple, 'Foo'),
    Item(Colors.blueGrey, 'Bar'),
    Item(Colors.lightGreen, 'Baz')
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Reordered List View in Flutter'),
      ),
      body: ReorderableListView(
        onReorder: (oldIndex, newIndex) {
          setState(() {
            final item = items.removeAt(oldIndex);
            items.insert(newIndex, item);
          });
        },
        children: items.map((i) => i.toListItem()).toList(),
      ),
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

Custom Stream Transformers in Dart



in this example we have created our own string transformer that
can trim a Stream<String> by trimming whitespace from both
beginning and end of the string
*/

import 'dart:convert' show utf8;

class StringTrimmer extends StreamTransformerBase<String, String> {
  const StringTrimmer();
  @override
  Stream<String> bind(Stream<String> stream) =>
      Stream.fromFuture(stream.join(' ')).map((str) => str.trim());
}

final string =
    '''   A long line of text with spaces in the beginning and the end, 
    divided into three lines just for the purpose of this demonstration    ''';

void testIt() async {
  final bytes = utf8.encode(string);
  final result = await Stream.value(bytes)
      .transform(utf8.decoder)
      .transform(LineSplitter())
      .transform(StringTrimmer())
      .join();
  print(result);
}

Expanding Stream Elements in Dart

/*


in this example we expand every element inside our Stream<int> to
a stream that in turn contains n+1 elements where n is the index generated
by our main stream, that's to say, 0, 1, 2, 3, 4, etc

*/
Stream<int> nestedEvents(int count) {
  return Stream.periodic(
    Duration(seconds: 1),
    (e) => e,
  ).take(count).asyncExpand(
        (i) => Stream.fromIterable(
          Iterable.generate(i + 1),
        ),
      );
}

void testIt() async {
  /* 
  prints the followings in this order
  0, 1
  0, 1, 2
  0, 1, 2, 3
  0, 1, 2, 3, 4
  */
  await for (final value in nestedEvents(5)) {
    print('Value is $value');
  }
}

Consume Streams for a Duration in Dart

extension TakeFor<T> on Stream<T> {
  Stream<T> takeFor(Duration duration) {
    final upTo = DateTime.now().add(duration);
    return takeWhile((_) {
      final now = DateTime.now();
      return now.isBefore(upTo) | now.isAtSameMomentAs(upTo);
    });
  }
}

Stream<DateTime> source() => Stream.periodic(
      Duration(milliseconds: 500),
      (_) => DateTime.now(),
    );

void testIt() async {
  await for (final dateTime in source().takeFor(
    Duration(seconds: 4),
  )) {
    print('date time is $dateTime');
  }
}

Shortening URLs in Dart

import 'dart:convert' show json;

Future<Uri> shortenUri(Uri uri, String bitlyToken) async {
  final client = HttpClient();

  final endpoint = Uri.https('api-ssl.bitly.com', '/v4/shorten');

  final response = await client.postUrl(endpoint).then(
    (req) {

      req.headers
        ..set(HttpHeaders.contentTypeHeader, 'application/json')
        ..set(HttpHeaders.authorizationHeader, 'Bearer $bitlyToken');

      final body = {
        'long_url': uri.toString(),
        'domain': 'bit.ly',
      };
      final bodyBytes = utf8.encode(json.encode(body));
      req.add(bodyBytes);

      return req.close();
    },
  );

  final responseBody = await response.transform(utf8.decoder).join();
  final responseJson = json.decode(responseBody) as Map<String, dynamic>;
  return Uri.parse(responseJson['link']);
}

void testIt() async {
  print(await shortenUri(
    Uri.parse('https://pixolity.se'),
    'XXX',
  ));
}

LimitedBox Widget as ListView Items in Flutter

const images = [
  'https://bit.ly/3x7J5Qt',
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/3jRSRCu',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3qYOtDm',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3yvFg7X',
  'https://bit.ly/3ywzOla',
  'https://bit.ly/3wnASpW',
  'https://bit.ly/3jXSDto',
];

extension ToListItemImage on String {
  Widget toListItemImage() {
    return LimitedBox(
      maxHeight: 150.0,
      child: Image.network(
        this,
        fit: BoxFit.fitWidth,
      ),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Limited Box in Flutter')),
      body: ListView(
        children: images.map((str) => str.toListItemImage()).toList(),
      ),
    );
  }
}

Generically Convert Anything to Int in Dart

extension ToInt on Object {
  int toInt() {
    final list = [
      if (this is Iterable<Object>)
        ...(List.of(this as Iterable<Object>))
      else if (this is int)
        [this as int]
      else
        (double.tryParse(toString()) ?? 0.0).round()
    ];
    return list
        .map((e) => (double.tryParse(e.toString()) ?? 0.0).round())
        .reduce((lhs, rhs) => lhs + rhs);
  }
}

void testIt() {
  assert(1.toInt() == 1);
  assert((2.2).toInt() == 2);
  assert((2.0).toInt() == 2);
  assert('3'.toInt() == 3);
  assert(['4', '5'].toInt() == 9);
  assert([4, 5].toInt() == 9);
  assert(['2.4', '3.5'].toInt() == 6);
  assert(['2', '3.5'].toInt() == 6);
  assert({'2', 3, '4.2'}.toInt() == 9);
  assert(['2', 3, '4.2', 5.3].toInt() == 14);
}

Validating URL Certificates in Dart

import 'dart:io' show HttpClient;

Future<bool> isSecuredWithValidCert(String uriString) async {
  final uri = Uri.parse(uriString);
  final client = HttpClient();
  try {
    await client.headUrl(uri).then((r) => r.close());
    return true;
  } on HandshakeException {
    return false;
  }
}

void testIt() async {
  await isSecuredWithValidCert('https://expired.badssl.com');
  await isSecuredWithValidCert('https://wrong.host.badssl.com');
  await isSecuredWithValidCert('https://self-signed.badssl.com');
  await isSecuredWithValidCert('https://untrusted-root.badssl.com');
  await isSecuredWithValidCert('https://revoked.badssl.com');
}

Displaying Popup Menus in Flutter

enum ImageAction { copy }

PopupMenuItem<ImageAction> copyButton({VoidCallback? onPressed}) =>
    PopupMenuItem<ImageAction>(
      value: ImageAction.copy,
      child: TextButton.icon(
        icon: Icon(Icons.copy),
        label: Text('Copy'),
        onPressed: onPressed,
      ),
    );

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter'),
      ),
      body: Center(
        child: PopupMenuButton<ImageAction>(
          elevation: 10,
          offset: Offset(0, 50),
          itemBuilder: (_) => [
            copyButton(
              onPressed: () {
                print('Copy the image...');
              },
            ),
          ],
          child: Image.network('https://bit.ly/3ywI8l6'),
        ),
      ),
    );
  }
}

Implementing Drag and Drop in Flutter

class HomePage extends StatefulWidget {
  HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  String? _imageUrl;

  bool shouldAccept(String? value) => Uri.tryParse(value ?? '') != null;

  Widget dragTargetBuilder(
    BuildContext context,
    List<String?> incoming,
    dynamic rejected,
  ) {
    final emptyContainer = Container(
      color: Colors.grey[200],
      height: 200,
      child: Center(
        child: Text('Drag an image here'),
      ),
    );

    if (incoming.isNotEmpty) {
      _imageUrl = incoming.first;
    }

    if (_imageUrl == null) {
      return emptyContainer;
    }

    try {
      final uri = Uri.parse(_imageUrl ?? '');
      return Container(
        color: Colors.grey[200],
        height: 200,
        child: Center(
          child: Image.network(uri.toString()),
        ),
      );
    } on FormatException {
      return emptyContainer;
    }
  }

  static final firstImageUrl = 'https://bit.ly/3xnoJTm';
  static final secondImageUrl = 'https://bit.ly/3hIuC78';
  final firstImage = Image.network(firstImageUrl);
  final secondImage = Image.network(secondImageUrl);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Tooltips in Flutter')),
      body: Padding(
        padding: const EdgeInsets.all(8.0),
        child: Column(
          children: [
            DragTarget<String>(
              onWillAccept: shouldAccept,
              builder: dragTargetBuilder,
            ),
            SizedBox(height: 10.0),
            DraggableImage(
              imageWidget: firstImage,
              imageUrl: firstImageUrl,
            ),
            SizedBox(height: 10.0),
            DraggableImage(
              imageWidget: secondImage,
              imageUrl: secondImageUrl,
            ),
          ],
        ),
      ),
    );
  }
}

class DraggableImage extends StatelessWidget {
  const DraggableImage({
    Key? key,
    required this.imageWidget,
    required this.imageUrl,
  }) : super(key: key);

  final Image imageWidget;
  final String imageUrl;

  @override
  Widget build(BuildContext context) {
    return Draggable<String>(
      data: imageUrl,
      feedback: Container(
        width: MediaQuery.of(context).size.width,
        decoration: BoxDecoration(
          boxShadow: [
            BoxShadow(
              blurRadius: 30,
              color: Colors.black,
              spreadRadius: 10,
            ),
          ],
        ),
        child: imageWidget,
      ),
      child: imageWidget,
    );
  }
}

Dismissing List Items in Flutter

const gridImages = [
  'https://bit.ly/3x7J5Qt',
  'https://bit.ly/3dLJNeD',
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/3jRSRCu',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3qYOtDm',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3yvFg7X',
  'https://bit.ly/3ywzOla',
  'https://bit.ly/3wnASpW',
  'https://bit.ly/3jXSDto',
];

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        slivers: [
          CustomAppBar(),
          CustomGridView(),
          CustomListView(
            imageUrls: gridImages,
          ),
        ],
      ),
    );
  }
}

class _CustomListViewState extends State<CustomListView> {
  @override
  Widget build(BuildContext context) {
    return SliverPadding(
      padding: EdgeInsets.all(8.0),
      sliver: SliverList(
        delegate: SliverChildBuilderDelegate(
          (context, index) {
            final url = widget.imageUrls[index];
            return Dismissible(
              key: ValueKey(url),
              onDismissed: (_) {
                widget.imageUrls.remove(url);
              },
              background: Container(
                color: Colors.red,
                child: FittedBox(
                  alignment: Alignment.centerRight,
                  fit: BoxFit.fitHeight,
                  child: Icon(Icons.delete, color: Colors.white),
                ),
              ),
              child: Padding(
                padding: const EdgeInsets.only(bottom: 8.0),
                child: Image.network(url),
              ),
            );
          },
          childCount: widget.imageUrls.length,
        ),
      ),
    );
  }
}

class CustomListView extends StatefulWidget {
  final List<String> imageUrls;

  const CustomListView({
    Key? key,
    required this.imageUrls,
  }) : super(key: key);

  @override
  _CustomListViewState createState() => _CustomListViewState();
}

class CustomGridView extends StatelessWidget {
  const CustomGridView({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SliverPadding(
      padding: EdgeInsets.all(8.0),
      sliver: SliverGrid(
        gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
          crossAxisCount: 3,
          mainAxisSpacing: 10,
          crossAxisSpacing: 10,
          childAspectRatio: 1.0,
        ),
        delegate: SliverChildBuilderDelegate(
          (context, index) {
            return Container(
              width: 100,
              height: 100,
              child: Image.network(gridImages[index]),
            );
          },
          childCount: gridImages.length,
        ),
      ),
    );
  }
}

class CustomAppBar extends StatelessWidget {
  const CustomAppBar({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SliverAppBar(
      backgroundColor: Colors.orange[300],
      forceElevated: true,
      pinned: false,
      snap: false,
      floating: true,
      expandedHeight: 172,
      flexibleSpace: FlexibleSpaceBar(
        title: Text(
          'Flutter',
          style: TextStyle(
            fontSize: 30,
            color: Colors.white,
            decoration: TextDecoration.underline,
          ),
        ),
        collapseMode: CollapseMode.parallax,
        background: Image.network('https://bit.ly/3x7J5Qt'),
      ),
    );
  }
}

Animating Widgets with Ease in Flutter

class Ball extends StatefulWidget {
  const Ball({Key? key}) : super(key: key);

  @override
  _BallState createState() => _BallState();
}

class _BallState extends State<Ball> with SingleTickerProviderStateMixin {
  late final AnimationController _controller;
  late final Animation _animation;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      vsync: this,
      duration: Duration(seconds: 4),
      reverseDuration: Duration(seconds: 4),
    );
    _animation = Tween(begin: 0.0, end: 2 * pi).animate(_controller);
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    _controller.repeat();
    return AnimatedBuilder(
      animation: _animation,
      builder: (context, image) {
        return Transform.rotate(
          angle: _animation.value,
          child: image,
        );
      },
      child: Image.network('https://bit.ly/3xspdrp'),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Animated Builder in Flutter'),
      ),
      body: Center(
        child: Ball(),
      ),
    );
  }
}

Displaying Tool Tips in Flutter

const imagesAndInfo = [
  ['https://bit.ly/3xnoJTm', 'Stockholm, Sweden'],
  ['https://bit.ly/3hIuC78', 'Dalarna, Sweden'],
  ['https://bit.ly/3wi9mdG', 'Brighton, UK'],
  ['https://bit.ly/3dSSMuy', 'Hove, UK'],
  ['https://bit.ly/3xoWCmV', 'Kerala, India'],
  ['https://bit.ly/3hGmjZC', 'Salvador da Bahia, Brazil']
];

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Tooltips in Flutter')),
      body: ListView.builder(
        itemCount: imagesAndInfo.length,
        itemBuilder: (_, index) {
          return Padding(
            padding: const EdgeInsets.only(top: 8.0, left: 8.0, right: 8.0),
            child: Tooltip(
              decoration: BoxDecoration(
                color: Colors.black,
                boxShadow: [
                  BoxShadow(
                    color: Colors.white.withAlpha(180),
                    offset: Offset.zero,
                    spreadRadius: 30.0,
                    blurRadius: 30.0,
                  ),
                ],
                borderRadius: BorderRadius.all(Radius.circular(8.0)),
              ),
              textStyle: TextStyle(fontSize: 20, color: Colors.white),
              message: imagesAndInfo[index][1],
              child: Image.network(
                imagesAndInfo[index][0],
              ),
            ),
          );
        },
      ),
    );
  }
}

Displaying Assorted Widgets Inside TableView in Flutter

const natureUrls = [
  'https://bit.ly/3dAtFwy',
  'https://bit.ly/36cHehe',
  'https://bit.ly/365uqt1',
  'https://bit.ly/3x7J5Qt',
  'https://bit.ly/3jBvJYU',
  'https://bit.ly/3yhbHHi'
];

extension ToImage on String {
  Widget toPaddedNetworkImage() => Padding(
        padding: const EdgeInsets.all(8.0),
        child: Image.network(this),
      );
}

extension ToImages on List<String> {
  List<Widget> toPaddedNetworkImages() =>
      map((str) => str.toPaddedNetworkImage()).toList();
}

extension ToTableRow on List<Widget> {
  TableRow toTableRow() => TableRow(children: this);
}

class ListPaginator<T> extends Iterable {
  final List<List<T>> list;
  ListPaginator({required List<T> input, required int itemsPerPage})
      : list = [
          for (var i = 0; i < input.length; i += itemsPerPage)
            input.getRange(i, min(input.length, i + itemsPerPage)).toList(),
        ];

  @override
  Iterator get iterator => list.iterator;
}

class HomePage extends StatelessWidget {
  final provider = ListPaginator<String>(
    input: natureUrls,
    itemsPerPage: 3,
  );
  HomePage({Key? key}) : super(key: key);

  Iterable<TableRow> getRows() sync* {
    for (final List<String> urlBatch in provider) {
      final networkImages = urlBatch.toPaddedNetworkImages();
      yield TableRow(children: networkImages);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('TableView in Flutter'),
      ),
      body: SingleChildScrollView(
        child: Table(
          defaultVerticalAlignment: TableCellVerticalAlignment.bottom,
          children: getRows().toList(),
        ),
      ),
    );
  }
}

Page Indicator with Page View in Flutter

const dashes = [
  'https://bit.ly/3gHlTCU',
  'https://bit.ly/3wOLO1c',
  'https://bit.ly/3cXWD9j',
  'https://bit.ly/3gT5Qk2',
];

class PageText extends StatelessWidget {
  final int current;
  final int total;

  const PageText({
    Key? key,
    required this.current,
    required this.total,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Text(
      'Page ${current + 1} of $total',
      style: TextStyle(fontSize: 30.0, shadows: [
        Shadow(
          offset: Offset(0.0, 1.0),
          blurRadius: 20.0,
          color: Colors.black.withAlpha(140),
        )
      ]),
    );
  }
}

class _HomePageState extends State<HomePage> {
  var _index = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Page Indicator')),
      body: SafeArea(
        child: Column(
          children: [
            Expanded(
              child: PageView.builder(
                onPageChanged: (pageIndex) {
                  setState(() => _index = pageIndex);
                },
                scrollDirection: Axis.horizontal,
                itemCount: dashes.length,
                itemBuilder: (context, index) {
                  return Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: [
                      Image.network(dashes[index]),
                      Text('Dash #${index + 1}'),
                    ],
                  );
                },
              ),
            ),
            PageText(current: _index, total: dashes.length)
          ],
        ),
      ),
    );
  }
}

Animating and Moving a Floating Action Button in Flutter

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

const List<FloatingActionButtonLocation> locations = [
  FloatingActionButtonLocation.centerDocked,
  FloatingActionButtonLocation.startDocked,
  FloatingActionButtonLocation.startFloat,
  FloatingActionButtonLocation.centerFloat,
  FloatingActionButtonLocation.endFloat,
  FloatingActionButtonLocation.endDocked
];

extension GoAround<T> on List<T> {
  T elementByGoingAround(int index) {
    final finalIndex = index >= length ? index.remainder(length) : index;
    return this[finalIndex];
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  var _locationIndex = 0;

  FloatingActionButtonLocation get location =>
      locations.elementByGoingAround(_locationIndex);

  @override
  Widget build(BuildContext context) {

    return Scaffold(
      appBar: AppBar(
        title: Text('Floating Action Button'),
      ),
      floatingActionButtonLocation: location,
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          setState(() => _locationIndex += 1);
        },
        child: Icon(Icons.add),
      ),
      bottomNavigationBar: BottomNavigationBar(
        backgroundColor: Colors.yellow[600],
        selectedItemColor: Colors.black,
        items: [
          BottomNavigationBarItem(
            icon: Icon(Icons.bedtime),
            label: 'Item 1',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.access_alarms),
            label: 'Item 2',
          )
        ],
        currentIndex: 0,
      ),
    );
  }
}

Fading Network Image Widget in Flutter

class FadingNetworkImage extends StatefulWidget {
  final String url;

  const FadingNetworkImage({Key? key, required this.url}) : super(key: key);

  @override
  _FadingNetworkImageState createState() => _FadingNetworkImageState();
}

class _FadingNetworkImageState extends State<FadingNetworkImage>
    with SingleTickerProviderStateMixin {
  late final AnimationController _controller;
  late final Animation<double> _animation;

  @override
  void initState() {
    super.initState();

    _controller =
        AnimationController(vsync: this, duration: Duration(seconds: 1));

    _animation = Tween(begin: 0.0, end: 1.0).animate(_controller);
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Image.network(
      widget.url,
      frameBuilder: (context, child, frame, wasSynchronouslyLoaded) {
        _controller.reset();
        _controller.forward();
        return FadeTransition(opacity: _animation, child: child);
      },
      loadingBuilder: (context, child, loadingProgress) {
        final totalBytes = loadingProgress?.expectedTotalBytes;
        final bytesLoaded = loadingProgress?.cumulativeBytesLoaded;
        if (totalBytes != null && bytesLoaded != null) {
          return LinearProgressIndicator(
            value: bytesLoaded / totalBytes,
          );
        } else {
          return child;
        }
      },
      errorBuilder: (context, error, stackTrace) {
        return Text('Error!');
      },
    );
  }
}

const dashes = [
  'https://bit.ly/3gHlTCU',
  'https://bit.ly/3wOLO1c',
  'https://bit.ly/3cXWD9j',
  'https://bit.ly/3gT5Qk2',
];

extension GoAround<T> on List<T> {
  T elementByGoingAround(int index) {
    final finalIndex = index >= length ? index.remainder(length) : index;
    return this[finalIndex];
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  int _index = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Faded Image'),
      ),
      body: Center(
          child: Column(
        children: [
          FadingNetworkImage(
            url: dashes.elementByGoingAround(_index),
          ),
          TextButton(
            onPressed: () {
              setState(() => _index += 1);
            },
            child: Text('Load next Dash'),
          ),
        ],
      )),
    );
  }
}

Transparent Alert Dialogs in Flutter

TextStyle get whiteTextStyle => TextStyle(color: Colors.white);

Future<void> showTextDialog({
  required BuildContext context,
  required String text,
}) {
  return showDialog(
    context: context,
    builder: (context) {
      return AlertDialog(
        shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.all(
            Radius.circular(10),
          ),
          side: BorderSide(
            color: Colors.white,
            style: BorderStyle.solid,
            width: 2,
          ),
        ),
        backgroundColor: Colors.black.withAlpha(150),
        titleTextStyle: whiteTextStyle,
        contentTextStyle: whiteTextStyle,
        content: Text(text),
        actions: [
          TextButton(
            style: TextButton.styleFrom(primary: Colors.white),
            onPressed: () {
              Navigator.of(context).pop();
            },
            child: Text('OK'),
          )
        ],
      );
    },
  );
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(
          'Rounded Corder Dialog',
        ),
      ),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Image.network('https://bit.ly/3ywI8l6'),
          TextButton(
            onPressed: () async {
              await showTextDialog(
                context: context,
                text: 'Hello world',
              );
            },
            child: Text('Show dialog'),
          ),
        ],
      ),
    );
  }
}

Network Image Size in Dart

import 'dart:ui' as ui;

Future<Size> getImageSize(String uri) {
  final image = Image.network('https://bit.ly/3dAtFwy');
  final comp = Completer<ui.Image>();
  image.image
      .resolve(
        ImageConfiguration.empty,
      )
      .addListener(
        ImageStreamListener(
          (ImageInfo info, _) => comp.complete(info.image),
        ),
      );
  return comp.future.then(
    (image) => Size(
      image.width.toDouble(),
      image.height.toDouble(),
    ),
  );
}

void testIt() async {
  final imageSize = await getImageSize('https://bit.ly/3dAtFwy');
  print(imageSize);
  assert(imageSize.width == 2048.0);
  assert(imageSize.height == 1365.0);
  print(imageSize.aspectRatio);
}

Animated Icons in Flutter

class _HomePageState extends State<HomePage>
    with SingleTickerProviderStateMixin {
  late final Animation<double> _animation;
  late final AnimationController _controller;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      vsync: this,
      duration: Duration(seconds: 1),
    );
    _animation = Tween(
      begin: 0.0,
      end: 1.0,
    ).animate(_controller);
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    _controller.repeat(reverse: true);
    return Scaffold(
      appBar: AppBar(
        title: Text('Animated Icons in Fluter'),
      ),
      body: Center(
        child: AnimatedIcon(
          color: Colors.green[300],
          size: MediaQuery.of(context).size.width,
          icon: AnimatedIcons.search_ellipsis,
          progress: _animation,
        ),
      ),
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

Custom Scroll Views in Flutter

const gridImages = [
  'https://bit.ly/3x7J5Qt',
  'https://bit.ly/3dLJNeD',
  'https://bit.ly/3ywI8l6',
  'https://bit.ly/3jRSRCu',
  'https://bit.ly/36fNNj9',
  'https://bit.ly/3jOueGG',
  'https://bit.ly/3qYOtDm',
  'https://bit.ly/3wt11Ec',
  'https://bit.ly/3yvFg7X',
  'https://bit.ly/3ywzOla',
  'https://bit.ly/3wnASpW',
  'https://bit.ly/3jXSDto',
];

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        slivers: [
          CustomAppBar(),
          CustomGridView(),
          CustomListView(),
        ],
      ),
    );
  }
}

class CustomListView extends StatelessWidget {
  const CustomListView({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SliverPadding(
      padding: EdgeInsets.all(8.0),
      sliver: SliverList(
        delegate: SliverChildBuilderDelegate(
          (context, index) {
            return Padding(
              padding: const EdgeInsets.only(bottom: 8.0),
              child: Image.network(gridImages[index]),
            );
          },
          childCount: gridImages.length,
        ),
      ),
    );
  }
}

class CustomGridView extends StatelessWidget {
  const CustomGridView({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SliverPadding(
      padding: EdgeInsets.all(8.0),
      sliver: SliverGrid(
        gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
          crossAxisCount: 3,
          mainAxisSpacing: 10,
          crossAxisSpacing: 10,
          childAspectRatio: 1.0,
        ),
        delegate: SliverChildBuilderDelegate(
          (context, index) {
            return Container(
              width: 100,
              height: 100,
              child: Image.network(gridImages[index]),
            );
          },
          childCount: gridImages.length,
        ),
      ),
    );
  }
}

class CustomAppBar extends StatelessWidget {
  const CustomAppBar({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SliverAppBar(
      backgroundColor: Colors.orange[300],
      forceElevated: true,
      pinned: false,
      snap: false,
      floating: true,
      expandedHeight: 172,
      flexibleSpace: FlexibleSpaceBar(
        title: Text(
          'Flutter',
          style: TextStyle(
            fontSize: 30,
            color: Colors.white,
            decoration: TextDecoration.underline,
          ),
        ),
        collapseMode: CollapseMode.parallax,
        background: Image.network('https://bit.ly/3x7J5Qt'),
      ),
    );
  }
}

Parallax App Bar in Flutter

JSON HTTP Requests in Dart

URL Timeouts in Dart

Detecting URL File Types in Dart

Paginated Lists in Dart

Requesting DELETE on APIs in Dart

Animated Containers in Flutter

Hiding Widgets in Flutter

Simple Opacity Animation in Flutter

Vignette Widget in Flutter

Drop Down Button Configuration and Usage in Flutter

Expandable List Items in Flutter

Infinite Scrolling in Flutter

Infinite Arrays in Dart

Custom Color Picker Component in Flutter

Displaying and Reacting to Switches in Flutter

Displaying Bottom Bars in Flutter

Displaying Buttons on AppBar in Flutter

Displaying Bottom Sheets in Flutter

Converting Enums to Radio Buttons in Flutter

Check Existence of Websites in Flutter

Images inside AlertDialog in Flutter

Returning Values from AlertDialog in Flutter

Simple Grid View in Flutter

Rendering Bullet Points in Flutter

Retrying Futures in Flutter

Containers as ClipOvals in Flutter

Rich Texts in Flutter

Wrapping Widgets in Flutter

Sweep Gradients in Flutter

Stream and StreamBuilder in Flutter

Blur Effect in Flutter

Convert Enums to Strings in Dart

Replacing Text in TextField in Flutter

Aspect Ratio in Flutter

Zoom and Pan in Flutter

Resizing Images in Flutter to Fit Screen Height

Validating URLs in Flutter

FrameBuilder for Network Images in Flutter

Adding Shadow to Icons in Flutter

Calculating Median of Lists in Dart

Generic Functions with Reduce in Dart

Passing Back Data From a Screen to the Previous One in Flutter

Flinging an Animation in Flutter

Fade Animations in Flutter

Throttling User Input in Flutter

Censoring TextFields in Flutter

Customizing TextButton in Flutter

Multiline TextFields in Flutter

Filtering TextField Input in Flutter

Focusing Manually on TextFields in Flutter

Data Streams Over HTTP/HTTPs in Dart

Catching Nonexistent Accessors or Methods in Dart

Using Expando in Dart

Implementing Custom Maps in Dart

Dynamically Calling Functions in Dart

Factory Constructors in Dart

Calculating the Sum of List Items in Dart

Removing Duplicate Strings in Lists in Dart (Case-Insensitive)

Implementing Range in Dart

Converting Lists to Maps in Dart

Implementing Hashable in Dart

Random Name Generator in Dart

Capturing Stack Traces in Dart Exceptions

Removing Duplicates from Lists in Dart

Optional Spread Operator in Dart

Calling Optional Functions in Dart

Odd-Even Sort in Dart

Implementing Zip and Tuples in Dart

Swapping Values in Lists with XOR in Dart

Waiting for Multiple Futures in Dart

Using Queues as Stacks in Dart

Custom Iterators in Dart

Iterables as Ranges and Transform in Dart

Errors vs Exceptions in Dart

Custom Annotations in Dart

Classes as Enums in Dart

Spread Operator in Collection Literals in Dart

StreamBuilder and StreamController in Dart

Almost Equal in Dart

Enum Associated Values in Dart

Implementing Comparable in Dart

Implementing Custom Integer Types in Dart

Custom Subscripts in Dart

Dart List Enumeration with Index

Applying Mixins to Other Mixins in Dart

Parameter Types in Dart

Custom Exceptions in Dart

rethrowing Exceptions in Dart

mixins and JSON Parsing in Dart

mixins vs abstract classes in Dart

Drawing Shapes in Flutter with LayoutBuilder, CustomPaint and CustomPainter

Generic Type Aliases in Dart

Callable Classes in Dart

Synchronous Generators in Dart

Implicit Interfaces in Dart

Did you know that in #Dart, every #class implicitly exports an #interface that can be #implemented (as opposed to #extended) by other classes? This is called "implicit interface".

Do you know how "const" constructors work in #Dart?

Did you know that in #Dart, it is actually preferred to use #async and #await over using raw #Futures?

In #Dart, you can use a combination of #Initializer #List plus default values for your class #member #fields to create elegant and handy convenience initializers

Did you know that in #Dart, you can extract elements of a certain type from your Lists using the #whereType #generic #function instead of calculating the #equality yourselves?

Do you know about #Type #Promotion in Dart?

"address" is an optional field of the "Person" class. If you look at the "doThis()" function you see that I'm saving the value of address in a local variable and then comparing it with null and then returning if it's null. The Dart compiler is intelligent enough to understand that after the if-statement, "address" is NOT null anymore since you've already compared it with null and returned from the function.

If you look at the "insteadOfThis" function, the first one, the Dart compiler cannot make the same assumption if you don't first store the value of address in a local variable. In that first function the Dart compiler, even after the if-statement, needs you to refer to address as an optional, using "address?" syntax.

The mechanism the Dart compiler uses in the "doThis()" function is called Type Promotion.

4 lines of #Dart code that include the #spread operator, #cascade #operator, #generics, #extensions, #private prefix and #getters

Functions as First Class Citizens in Dart

Download Details: 
Author: vandadnp
Source Code: https://github.com/vandadnp/flutter-tips-and-tricks

#flutter #dart #programming #developer 

Adaline  Kulas

Adaline Kulas

1594162500

Multi-cloud Spending: 8 Tips To Lower Cost

A multi-cloud approach is nothing but leveraging two or more cloud platforms for meeting the various business requirements of an enterprise. The multi-cloud IT environment incorporates different clouds from multiple vendors and negates the dependence on a single public cloud service provider. Thus enterprises can choose specific services from multiple public clouds and reap the benefits of each.

Given its affordability and agility, most enterprises opt for a multi-cloud approach in cloud computing now. A 2018 survey on the public cloud services market points out that 81% of the respondents use services from two or more providers. Subsequently, the cloud computing services market has reported incredible growth in recent times. The worldwide public cloud services market is all set to reach $500 billion in the next four years, according to IDC.

By choosing multi-cloud solutions strategically, enterprises can optimize the benefits of cloud computing and aim for some key competitive advantages. They can avoid the lengthy and cumbersome processes involved in buying, installing and testing high-priced systems. The IaaS and PaaS solutions have become a windfall for the enterprise’s budget as it does not incur huge up-front capital expenditure.

However, cost optimization is still a challenge while facilitating a multi-cloud environment and a large number of enterprises end up overpaying with or without realizing it. The below-mentioned tips would help you ensure the money is spent wisely on cloud computing services.

  • Deactivate underused or unattached resources

Most organizations tend to get wrong with simple things which turn out to be the root cause for needless spending and resource wastage. The first step to cost optimization in your cloud strategy is to identify underutilized resources that you have been paying for.

Enterprises often continue to pay for resources that have been purchased earlier but are no longer useful. Identifying such unused and unattached resources and deactivating it on a regular basis brings you one step closer to cost optimization. If needed, you can deploy automated cloud management tools that are largely helpful in providing the analytics needed to optimize the cloud spending and cut costs on an ongoing basis.

  • Figure out idle instances

Another key cost optimization strategy is to identify the idle computing instances and consolidate them into fewer instances. An idle computing instance may require a CPU utilization level of 1-5%, but you may be billed by the service provider for 100% for the same instance.

Every enterprise will have such non-production instances that constitute unnecessary storage space and lead to overpaying. Re-evaluating your resource allocations regularly and removing unnecessary storage may help you save money significantly. Resource allocation is not only a matter of CPU and memory but also it is linked to the storage, network, and various other factors.

  • Deploy monitoring mechanisms

The key to efficient cost reduction in cloud computing technology lies in proactive monitoring. A comprehensive view of the cloud usage helps enterprises to monitor and minimize unnecessary spending. You can make use of various mechanisms for monitoring computing demand.

For instance, you can use a heatmap to understand the highs and lows in computing visually. This heat map indicates the start and stop times which in turn lead to reduced costs. You can also deploy automated tools that help organizations to schedule instances to start and stop. By following a heatmap, you can understand whether it is safe to shut down servers on holidays or weekends.

#cloud computing services #all #hybrid cloud #cloud #multi-cloud strategy #cloud spend #multi-cloud spending #multi cloud adoption #why multi cloud #multi cloud trends #multi cloud companies #multi cloud research #multi cloud market

Rupert  Beatty

Rupert Beatty

1666245660

A Collection Of Swift Tips & Tricks That I've Shared on Twitter

Swift tips & tricks ⚡️

One of the things I really love about Swift is how I keep finding interesting ways to use it in various situations, and when I do - I usually share them on Twitter. Here's a collection of all the tips & tricks that I've shared so far. Each entry has a link to the original tweet, if you want to respond with some feedback or question, which is always super welcome! 🚀

⚠️ This list is no longer being updated. For my latest Swift tips, checkout the "Tips" section on Swift by Sundell.

Also make sure to check out all of my other Swift content:

102 Making async tests faster and more stable

🚀 Here are some quick tips to make async tests faster & more stable:

  • 😴 Avoid sleep() - use expectations instead
  • ⏱ Use generous timeouts to avoid flakiness on CI
  • 🧐 Put all assertions at the end of each test, not inside closures
// BEFORE:

class MentionDetectorTests: XCTestCase {
    func testDetectingMention() {
        let detector = MentionDetector()
        let string = "This test was written by @johnsundell."

        detector.detectMentions(in: string) { mentions in
            XCTAssertEqual(mentions, ["johnsundell"])
        }
        
        sleep(2)
    }
}

// AFTER:

class MentionDetectorTests: XCTestCase {
    func testDetectingMention() {
        let detector = MentionDetector()
        let string = "This test was written by @johnsundell."

        var mentions: [String]?
        let expectation = self.expectation(description: #function)

        detector.detectMentions(in: string) {
            mentions = $0
            expectation.fulfill()
        }

        waitForExpectations(timeout: 10)
        XCTAssertEqual(mentions, ["johnsundell"])
    }
}

For more on async testing, check out "Unit testing asynchronous Swift code".

101 Adding support for Apple Pencil double-taps

✍️ Adding support for the new Apple Pencil double-tap feature is super easy! All you have to do is to create a UIPencilInteraction, add it to a view, and implement one delegate method. Hopefully all pencil-compatible apps will soon adopt this.

let interaction = UIPencilInteraction()
interaction.delegate = self
view.addInteraction(interaction)

extension ViewController: UIPencilInteractionDelegate {
    func pencilInteractionDidTap(_ interaction: UIPencilInteraction) {
        // Handle pencil double-tap
    }
}

For more on using this and other iPad Pro features, check out "Building iPad Pro features in Swift".

100 Combining values with functions

😎 Here's a cool function that combines a value with a function to return a closure that captures that value, so that it can be called without any arguments. Super useful when working with closure-based APIs and we want to use some of our properties without having to capture self.

func combine<A, B>(_ value: A, with closure: @escaping (A) -> B) -> () -> B {
    return { closure(value) }
}

// BEFORE:

class ProductViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        buyButton.handler = { [weak self] in
            guard let self = self else {
                return
            }
            
            self.productManager.startCheckout(for: self.product)
        }
    }
}

// AFTER:

class ProductViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        buyButton.handler = combine(product, with: productManager.startCheckout)
    }
}

99 Dependency injection using functions

💉 When I'm only using a single function from a dependency, I love to inject that function as a closure, instead of having to create a protocol and inject the whole object. Makes dependency injection & testing super simple.

final class ArticleLoader {
    typealias Networking = (Endpoint) -> Future<Data>
    
    private let networking: Networking
    
    init(networking: @escaping Networking = URLSession.shared.load) {
        self.networking = networking
    }
    
    func loadLatest() -> Future<[Article]> {
        return networking(.latestArticles).decode()
    }
}

For more on this technique, check out "Simple Swift dependency injection with functions".

98 Using a custom exception handler

💥 It's cool that you can easily assign a closure as a custom NSException handler. This is super useful when building things in Playgrounds - since you can't use breakpoints - so instead of just signal SIGABRT, you'll get the full exception description if something goes wrong.

NSSetUncaughtExceptionHandler { exception in
    print(exception)
}

97 Using type aliases to give semantic meaning to primitives

❤️ I love that in Swift, we can use the type system to make our code so much more self-documenting - one way of doing so is to use type aliases to give the primitive types that we use a more semantic meaning.

extension List.Item {
    // Using type aliases, we can give semantic meaning to the
    // primitive types that we use, without having to introduce
    // wrapper types.
    typealias Index = Int
}

extension List {
    enum Mutation {
        // Our enum cases now become a lot more self-documenting,
        // without having to add additional parameter labels to
        // explain them.
        case add(Item, Item.Index)
        case update(Item, Item.Index)
        case remove(Item.Index)
    }
}

For more on self-documenting code, check out "Writing self-documenting Swift code".

96 Specializing protocols using constraints

🤯 A little late night prototyping session reveals that protocol constraints can not only be applied to extensions - they can also be added to protocol definitions!

This is awesome, since it lets us easily define specialized protocols based on more generic ones.

protocol Component {
    associatedtype Container
    func add(to container: Container)
}

// Protocols that inherit from other protocols can include
// constraints to further specialize them.
protocol ViewComponent: Component where Container == UIView {
    associatedtype View: UIView
    var view: View { get }
}

extension ViewComponent {
    func add(to container: UIView) {
        container.addSubview(view)
    }
}

For more on specializing protocols, check out "Specializing protocols in Swift".

95 Unwrapping an optional or throwing an error

📦 Here's a super handy extension on Swift's Optional type, which gives us a really nice API for easily unwrapping an optional, or throwing an error in case the value turned out to be nil:

extension Optional {
    func orThrow(_ errorExpression: @autoclosure () -> Error) throws -> Wrapped {
        switch self {
        case .some(let value):
            return value
        case .none:
            throw errorExpression()
        }
    }
}

let file = try loadFile(at: path).orThrow(MissingFileError())

For more ways that optionals can be extended, check out "Extending optionals in Swift".

94 Testing code that uses static APIs

👩‍🔬 Testing code that uses static APIs can be really tricky, but there's a way that it can often be done - using Swift's first class function capabilities!

Instead of accessing that static API directly, we can inject the function we want to use, which enables us to mock it!

// BEFORE

class FriendsLoader {
    func loadFriends(then handler: @escaping (Result<[Friend]>) -> Void) {
        Networking.loadData(from: .friends) { result in
            ...
        }
    }
}

// AFTER

class FriendsLoader {
    typealias Handler<T> = (Result<T>) -> Void
    typealias DataLoadingFunction = (Endpoint, @escaping Handler<Data>) -> Void

    func loadFriends(using dataLoading: DataLoadingFunction = Networking.loadData,
                     then handler: @escaping Handler<[Friend]>) {
        dataLoading(.friends) { result in
            ...
        }
    }
}

// MOCKING IN TESTS

let dataLoading: FriendsLoader.DataLoadingFunction = { _, handler in
    handler(.success(mockData))
}

friendsLoader.loadFriends(using: dataLoading) { result in
    ...
}

93 Matching multiple enum cases with associated values

🐾 Swift's pattern matching capabilities are so powerful! Two enum cases with associated values can even be matched and handled by the same switch case - which is super useful when handling state changes with similar data.

enum DownloadState {
    case inProgress(progress: Double)
    case paused(progress: Double)
    case cancelled
    case finished(Data)
}

func downloadStateDidChange(to state: DownloadState) {
    switch state {
    case .inProgress(let progress), .paused(let progress):
        updateProgressView(with: progress)
    case .cancelled:
        showCancelledMessage()
    case .finished(let data):
        process(data)
    }
}

92 Multiline string literals

🅰 One really nice benefit of Swift multiline string literals - even for single lines of text - is that they don't require quotes to be escaped. Perfect when working with things like HTML, or creating a custom description for an object.

let html = highlighter.highlight("Array<String>")

XCTAssertEqual(html, """
<span class="type">Array</span>&lt;<span class="type">String</span>&gt;
""")

91 Reducing sequences

💎 While it's very common in functional programming, the reduce function might be a bit of a hidden gem in Swift. It provides a super useful way to transform a sequence into a single value.

extension Sequence where Element: Equatable {
    func numberOfOccurrences(of target: Element) -> Int {
        return reduce(0) { result, element in
            guard element == target else {
                return result
            }

            return result + 1
        }
    }
}

You can read more about transforming collections in "Transforming collections in Swift".

90 Avoiding manual Codable implementations

📦 When I use Codable in Swift, I want to avoid manual implementations as much as possible, even when there's a mismatch between my code structure and the JSON I'm decoding.

One way that can often be achieved is to use private data containers combined with computed properties.

struct User: Codable {
    let name: String
    let age: Int

    var homeTown: String { return originPlace.name }

    private let originPlace: Place
}

private extension User {
    struct Place: Codable {
        let name: String
    }
}

extension User {
    struct Container: Codable {
        let user: User
    }
}

89 Using feature flags instead of feature branches

🚢 Instead of using feature branches, I merge almost all of my code directly into master - and then I use feature flags to conditionally enable features when they're ready. That way I can avoid merge conflicts and keep shipping!

extension ListViewController {
    func addSearchIfNeeded() {
        // Rather than having to keep maintaining a separate
        // feature branch for a new feature, we can use a flag
        // to conditionally turn it on.
        guard FeatureFlags.searchEnabled else {
            return
        }

        let resultsVC = SearchResultsViewController()
        let searchVC = UISearchController(
            searchResultsController: resultsVC
        )

        searchVC.searchResultsUpdater = resultsVC
        navigationItem.searchController = searchVC
    }
}

You can read more about feature flags in "Feature flags in Swift".

88 Lightweight data hierarchies using tuples

💾 Here I'm using tuples to create a lightweight hierarchy for my data, giving me a nice structure without having to introduce any additional types.

struct CodeSegment {
    var tokens: (
        previous: String?,
        current: String
    )

    var delimiters: (
        previous: Character?
        next: Character?
    )
}

handle(segment.tokens.current)

You can read more about tuples in "Using tuples as lightweight types in Swift"

87 The rule of threes

3️⃣ Whenever I have 3 properties or local variables that share the same prefix, I usually try to extract them into their own method or type. That way I can avoid massive types & methods, and also increase readability, without falling into a "premature optimization" trap.

Before

public func generate() throws {
    let contentFolder = try folder.subfolder(named: "content")

    let articleFolder = try contentFolder.subfolder(named: "posts")
    let articleProcessor = ContentProcessor(folder: articleFolder)
    let articles = try articleProcessor.process()

    ...
}

After

public func generate() throws {
    let contentFolder = try folder.subfolder(named: "content")
    let articles = try processArticles(in: contentFolder)
    ...
}

private func processArticles(in folder: Folder) throws -> [ContentItem] {
    let folder = try folder.subfolder(named: "posts")
    let processor = ContentProcessor(folder: folder)
    return try processor.process()
}

86 Useful Codable extensions

👨‍🔧 Here's two extensions that I always add to the Encodable & Decodable protocols, which for me really make the Codable API nicer to use. By using type inference for decoding, a lot of boilerplate can be removed when the compiler is already able to infer the resulting type.

extension Encodable {
    func encoded() throws -> Data {
        return try JSONEncoder().encode(self)
    }
}

extension Data {
    func decoded<T: Decodable>() throws -> T {
        return try JSONDecoder().decode(T.self, from: self)
    }
}

let data = try user.encoded()

// By using a generic type in the decoded() method, the
// compiler can often infer the type we want to decode
// from the current context.
try userDidLogin(data.decoded())

// And if not, we can always supply the type, still making
// the call site read very nicely.
let otherUser = try data.decoded() as User

85 Using shared UserDefaults suites

📦 UserDefaults is a lot more powerful than what it first might seem like. Not only can it store more complex values (like dates & dictionaries) and parse command line arguments - it also enables easy sharing of settings & lightweight data between apps in the same App Group.

let sharedDefaults = UserDefaults(suiteName: "my-app-group")!
let useDarkMode = sharedDefaults.bool(forKey: "dark-mode")

// This value is put into the shared suite.
sharedDefaults.set(true, forKey: "dark-mode")

// If you want to treat the shared settings as read-only (and add
// local overrides on top of them), you can simply add the shared
// suite to the standard UserDefaults.
let combinedDefaults = UserDefaults.standard
combinedDefaults.addSuite(named: "my-app-group")

// This value is a local override, not added to the shared suite.
combinedDefaults.set(true, forKey: "app-specific-override")

84 Custom UIView backing layers

🎨 By overriding layerClass you can tell UIKit what CALayer class to use for a UIView's backing layer. That way you can reduce the amount of layers, and don't have to do any manual layout.

final class GradientView: UIView {
    override class var layerClass: AnyClass { return CAGradientLayer.self }

    var colors: (start: UIColor, end: UIColor)? {
        didSet { updateLayer() }
    }

    private func updateLayer() {
        let layer = self.layer as! CAGradientLayer
        layer.colors = colors.map { [$0.start.cgColor, $0.end.cgColor] }
    }
}

83 Auto-Equatable enums with associated values

✅ That the compiler now automatically synthesizes Equatable conformances is such a huge upgrade for Swift! And the cool thing is that it works for all kinds of types - even for enums with associated values! Especially useful when using enums for verification in unit tests.

struct Article: Equatable {
    let title: String
    let text: String
}

struct User: Equatable {
    let name: String
    let age: Int
}

extension Navigator {
    enum Destination: Equatable {
        case profile(User)
        case article(Article)
    }
}

func testNavigatingToArticle() {
    let article = Article(title: "Title", text: "Text")
    controller.select(article)
    XCTAssertEqual(navigator.destinations, [.article(article)])
}

82 Defaults for associated types

🤝 Associated types can have defaults in Swift - which is super useful for types that are not easily inferred (for example when they're not used for a specific instance method or property).

protocol Identifiable {
    associatedtype RawIdentifier: Codable = String

    var id: Identifier<Self> { get }
}

struct User: Identifiable {
    let id: Identifier<User>
    let name: String
}

struct Group: Identifiable {
    typealias RawIdentifier = Int

    let id: Identifier<Group>
    let name: String
}

81 Creating a dedicated identifier type

🆔 If you want to avoid using plain strings as identifiers (which can increase both type safety & readability), it's really easy to create a custom Identifier type that feels just like a native Swift type, thanks to protocols!

More on this topic in "Type-safe identifiers in Swift".

struct Identifier: Hashable {
    let string: String
}

extension Identifier: ExpressibleByStringLiteral {
    init(stringLiteral value: String) {
        string = value
    }
}

extension Identifier: CustomStringConvertible {
    var description: String {
        return string
    }
}

extension Identifier: Codable {
    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        string = try container.decode(String.self)
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        try container.encode(string)
    }
}

struct Article: Codable {
    let id: Identifier
    let title: String
}

let article = Article(id: "my-article", title: "Hello world!")

80 Assigning optional tuple members to variables

🙌 A really cool thing about using tuples to model the internal state of a Swift type, is that you can unwrap an optional tuple's members directly into local variables.

Very useful in order to group multiple optional values together for easy unwrapping & handling.

class ImageTransformer {
    private var queue = [(image: UIImage, transform: Transform)]()

    private func processNext() {
        // When unwrapping an optional tuple, you can assign the members
        // directly to local variables.
        guard let (image, transform) = queue.first else {
            return
        }

        let context = Context()
        context.draw(image)
        context.apply(transform)
        ...
    }
}

79 Struct convenience initializers

❤️ I love to structure my code using extensions in Swift. One big benefit of doing so when it comes to struct initializers, is that defining a convenience initializer doesn't remove the default one the compiler generates - best of both worlds!

struct Article {
    let date: Date
    var title: String
    var text: String
    var comments: [Comment]
}

extension Article {
    init(title: String, text: String) {
        self.init(date: Date(), title: title, text: text, comments: [])
    }
}

let articleA = Article(title: "Best Cupcake Recipe", text: "...")

let articleB = Article(
    date: Date(),
    title: "Best Cupcake Recipe",
    text: "...",
    comments: [
        Comment(user: currentUser, text: "Yep, can confirm!")
    ]
)

78 Usages of throwing functions

🏈 A big benefit of using throwing functions for synchronous Swift APIs is that the caller can decide whether they want to treat the return value as optional (try?) or required (try).

func loadFile(named name: String) throws -> File {
    guard let url = urlForFile(named: name) else {
        throw File.Error.missing
    }

    do {
        let data = try Data(contentsOf: url)
        return File(url: url, data: data)
    } catch {
        throw File.Error.invalidData(error)
    }
}

let requiredFile = try loadFile(named: "AppConfig.json")

let optionalFile = try? loadFile(named: "UserSettings.json")

77 Nested generic types

🐝 Types that are nested in generics automatically inherit their parent's generic types - which is super useful when defining accessory types (for things like states or outcomes).

struct Task<Input, Output> {
    typealias Closure = (Input) throws -> Output

    let closure: Closure
}

extension Task {
    enum Result {
        case success(Output)
        case failure(Error)
    }
}

76 Equatable & Hashable structures

🤖 Now that the Swift compiler automatically synthesizes Equatable & Hashable conformances for value types, it's easier than ever to setup model structures with nested types that are all Equatable/Hashable!

typealias Value = Hashable & Codable

struct User: Value {
    var name: String
    var age: Int
    var lastLoginDate: Date?
    var settings: Settings
}

extension User {
    struct Settings: Value {
        var itemsPerPage: Int
        var theme: Theme
    }
}

extension User.Settings {
    enum Theme: String, Value {
        case light
        case dark
    }
}

You can read more about using nested types in Swift here.

75 Conditional conformances

🎉 Swift 4.1 is here! One of the key features it brings is conditional conformances, which lets you have a type only conform to a protocol under certain constraints.

protocol UnboxTransformable {
    associatedtype RawValue

    static func transform(_ value: RawValue) throws -> Self?
}

extension Array: UnboxTransformable where Element: UnboxTransformable {
    typealias RawValue = [Element.RawValue]

    static func transform(_ value: RawValue) throws -> [Element]? {
        return try value.compactMap(Element.transform)
    }
}

I also have an article with lots of more info on conditional conformances here. Paul Hudson also has a great overview of all Swift 4.1 features here.

74 Generic type aliases

🕵️‍♀️ A cool thing about Swift type aliases is that they can be generic! Combine that with tuples and you can easily define simple generic types.

typealias Pair<T> = (T, T)

extension Game {
    func calculateScore(for players: Pair<Player>) -> Int {
        ...
    }
}

You can read more about using tuples as lightweight types here.

73 Parsing command line arguments using UserDefaults

☑️ A really cool "hidden" feature of UserDefaults is that it contains any arguments that were passed to the app at launch!

Super useful both in Swift command line tools & scripts, but also to temporarily override a value when debugging iOS apps.

let defaults = UserDefaults.standard
let query = defaults.string(forKey: "query")
let resultCount = defaults.integer(forKey: "results")

72 Using the & operator

👏 Swift's & operator is awesome! Not only can you use it to compose protocols, you can compose other types too! Very useful if you want to hide concrete types & implementation details.

protocol LoadableFromURL {
    func load(from url: URL)
}

class ContentViewController: UIViewController, LoadableFromURL {
    func load(from url: URL) {
        ...
    }
}

class ViewControllerFactory {
    func makeContentViewController() -> UIViewController & LoadableFromURL {
        return ContentViewController()
    }
}

71 Capturing multiple values in mocks

🤗 When capturing values in mocks, using an array (instead of just a single value) makes it easy to verify that only a certain number of values were passed.

Perfect for protecting against "over-calling" something.

class UserManagerTests: XCTestCase {
    func testObserversCalledWhenUserFirstLogsIn() {
        let manager = UserManager()

        let observer = ObserverMock()
        manager.addObserver(observer)

        // First login, observers should be notified
        let user = User(id: 123, name: "John")
        manager.userDidLogin(user)
        XCTAssertEqual(observer.users, [user])

        // If the same user logs in again, observers shouldn't be notified
        manager.userDidLogin(user)
        XCTAssertEqual(observer.users, [user])
    }
}

private extension UserManagerTests {
    class ObserverMock: UserManagerObserver {
        private(set) var users = [User]()

        func userDidChange(to user: User) {
            users.append(user)
        }
    }
}

70 Reducing the need for mocks

👋 When writing tests, you don't always need to create mocks - you can create stubs using real instances of things like errors, URLs & UserDefaults.

Here's how to do that for some common tasks/object types in Swift:

// Create errors using NSError (#function can be used to reference the name of the test)
let error = NSError(domain: #function, code: 1, userInfo: nil)

// Create non-optional URLs using file paths
let url = URL(fileURLWithPath: "Some/URL")

// Reference the test bundle using Bundle(for:)
let bundle = Bundle(for: type(of: self))

// Create an explicit UserDefaults object (instead of having to use a mock)
let userDefaults = UserDefaults(suiteName: #function)

// Create queues to control/await concurrent operations
let queue = DispatchQueue(label: #function)

For when you actually do need mocking, check out "Mocking in Swift".

69 Using "then" as an external parameter label for closures

⏱ I've started using "then" as an external parameter label for completion handlers. Makes the call site read really nicely (Because I do ❤️ conversational API design) regardless of whether trailing closure syntax is used or not.

protocol DataLoader {
    // Adding type aliases to protocols can be a great way to
    // reduce verbosity for parameter types.
    typealias Handler = (Result<Data>) -> Void
    associatedtype Endpoint

    func loadData(from endpoint: Endpoint, then handler: @escaping Handler)
}

loader.loadData(from: .messages) { result in
    ...
}

loader.loadData(from: .messages, then: { result in
    ...
})

68 Combining lazily evaluated sequences with the builder pattern

😴 Combining lazily evaluated sequences with builder pattern-like properties can lead to some pretty sweet APIs for configurable sequences in Swift.

Also useful for queries & other things you "build up" and then execute.

// Extension adding builder pattern-like properties that return
// a new sequence value with the given configuration applied
extension FileSequence {
    var recursive: FileSequence {
        var sequence = self
        sequence.isRecursive = true
        return sequence
    }

    var includingHidden: FileSequence {
        var sequence = self
        sequence.includeHidden = true
        return sequence
    }
}

// BEFORE

let files = folder.makeFileSequence(recursive: true, includeHidden: true)

// AFTER

let files = folder.files.recursive.includingHidden

Want an intro to lazy sequences? Check out "Swift sequences: The art of being lazy".

67 Faster & more stable UI tests

My top 3 tips for faster & more stable UI tests:

📱 Reset the app's state at the beginning of every test.

🆔 Use accessibility identifiers instead of UI strings.

⏱ Use expectations instead of waiting time.

func testOpeningArticle() {
    // Launch the app with an argument that tells it to reset its state
    let app = XCUIApplication()
    app.launchArguments.append("--uitesting")
    app.launch()
    
    // Check that the app is displaying an activity indicator
    let activityIndicator = app.activityIndicator.element
    XCTAssertTrue(activityIndicator.exists)
    
    // Wait for the loading indicator to disappear = content is ready
    expectation(for: NSPredicate(format: "exists == 0"),
                evaluatedWith: activityIndicator)
                
    // Use a generous timeout in case the network is slow
    waitForExpectations(timeout: 10)
    
    // Tap the cell for the first article
    app.tables.cells["Article.0"].tap()
    
    // Assert that a label with the accessibility identifier "Article.Title" exists
    let label = app.staticTexts["Article.Title"]
    XCTAssertTrue(label.exists)
}

66 Accessing the clipboard from a Swift script

📋 It's super easy to access the contents of the clipboard from a Swift script. A big benefit of Swift scripting is being able to use Cocoa's powerful APIs for Mac apps.

import Cocoa

let clipboard = NSPasteboard.general.string(forType: .string)

65 Using tuples for view state

🎯 Using Swift tuples for view state can be a super nice way to group multiple properties together and render them reactively using the layout system.

By using a tuple we don't have to either introduce a new type or make our view model-aware.

class TextView: UIView {
    var state: (title: String?, text: String?) {
        // By telling UIKit that our view needs layout and binding our
        // state in layoutSubviews, we can react to state changes without
        // doing unnecessary layout work.
        didSet { setNeedsLayout() }
    }

    private let titleLabel = UILabel()
    private let textLabel = UILabel()

    override func layoutSubviews() {
        super.layoutSubviews()

        titleLabel.text = state.title
        textLabel.text = state.text

        ...
    }
}

64 Throwing tests and LocalizedError

⚾️ Swift tests can throw, which is super useful in order to avoid complicated logic or force unwrapping. By making errors conform to LocalizedError, you can also get a nice error message in Xcode if there's a failure.

class ImageCacheTests: XCTestCase {
    func testCachingAndLoadingImage() throws {
        let bundle = Bundle(for: type(of: self))
        let cache = ImageCache(bundle: bundle)
        
        // Bonus tip: You can easily load images from your test
        // bundle using this UIImage initializer
        let image = try require(UIImage(named: "sample", in: bundle, compatibleWith: nil))
        try cache.cache(image, forKey: "key")
        
        let cachedImage = try cache.image(forKey: "key")
        XCTAssertEqual(image, cachedImage)
    }
}

enum ImageCacheError {
    case emptyKey
    case dataConversionFailed
}

// When using throwing tests, making your errors conform to
// LocalizedError will render a much nicer error message in
// Xcode (per default only the error code is shown).
extension ImageCacheError: LocalizedError {
    var errorDescription: String? {
        switch self {
        case .emptyKey:
            return "An empty key was given"
        case .dataConversionFailed:
            return "Failed to convert the given image to Data"
        }
    }
}

For more information, and the implementation of the require method used above, check out "Avoiding force unwrapping in Swift unit tests".

63 The difference between static and class properties

✍️ Unlike static properties, class properties can be overridden by subclasses (however, they can't be stored, only computed).

class TableViewCell: UITableViewCell {
    class var preferredHeight: CGFloat { return 60 }
}

class TallTableViewCell: TableViewCell {
    override class var preferredHeight: CGFloat { return 100 }
}

62 Creating extensions with static factory methods

👨‍🎨 Creating extensions with static factory methods can be a great alternative to subclassing in Swift, especially for things like setting up UIViews, CALayers or other kinds of styling.

It also lets you remove a lot of styling & setup from your view controllers.

extension UILabel {
    static func makeForTitle() -> UILabel {
        let label = UILabel()
        label.font = .boldSystemFont(ofSize: 24)
        label.textColor = .darkGray
        label.adjustsFontSizeToFitWidth = true
        label.minimumScaleFactor = 0.75
        return label
    }

    static func makeForText() -> UILabel {
        let label = UILabel()
        label.font = .systemFont(ofSize: 16)
        label.textColor = .black
        label.numberOfLines = 0
        return label
    }
}

class ArticleViewController: UIViewController {
    lazy var titleLabel = UILabel.makeForTitle()
    lazy var textLabel = UILabel.makeForText()
}

61 Child view controller auto-resizing

🧒 An awesome thing about child view controllers is that they're automatically resized to match their parent, making them a super nice solution for things like loading & error views.

class ListViewController: UIViewController {
    func loadItems() {
        let loadingViewController = LoadingViewController()
        add(loadingViewController)

        dataLoader.loadItems { [weak self] result in
            loadingViewController.remove()
            self?.handle(result)
        }
    }
}

For more about child view controller (including the add and remove methods used above), check out "Using child view controllers as plugins in Swift".

60 Using zip

🤐 Using the zip function in Swift you can easily combine two sequences. Super useful when using two sequences to do some work, since zip takes care of all the bounds-checking.

func render(titles: [String]) {
    for (label, text) in zip(titleLabels, titles) {
        print(text)
        label.text = text
    }
}

59 Defining custom option sets

🎛 The awesome thing about option sets in Swift is that they can automatically either be passed as a single member or as a set. Even cooler is that you can easily define your own option sets as well, perfect for options and other non-exclusive values.

// Option sets are awesome, because you can easily pass them
// both using dot syntax and array literal syntax, like when
// using the UIView animation API:
UIView.animate(withDuration: 0.3,
               delay: 0,
               options: .allowUserInteraction,
               animations: animations)

UIView.animate(withDuration: 0.3,
               delay: 0,
               options: [.allowUserInteraction, .layoutSubviews],
               animations: animations)

// The cool thing is that you can easily define your own option
// sets as well, by defining a struct that has an Int rawValue,
// that will be used as a bit mask.
extension Cache {
    struct Options: OptionSet {
        static let saveToDisk = Options(rawValue: 1)
        static let clearOnMemoryWarning = Options(rawValue: 1 << 1)
        static let clearDaily = Options(rawValue: 1 << 2)

        let rawValue: Int
    }
}

// We can now use Cache.Options just like UIViewAnimationOptions:
Cache(options: .saveToDisk)
Cache(options: [.saveToDisk, .clearDaily])

58 Using the where clause with associated types

🙌 Using the where clause when designing protocol-oriented APIs in Swift can let your implementations (or others' if it's open source) have a lot more freedom, especially when it comes to collections.

See "Using generic type constraints in Swift 4" for more info.

public protocol PathFinderMap {
    associatedtype Node
    // Using the 'where' clause for associated types, we can
    // ensure that a type meets certain requirements (in this
    // case that it's a sequence with Node elements).
    associatedtype NodeSequence: Sequence where NodeSequence.Element == Node

    // Instead of using a concrete type (like [Node]) here, we
    // give implementors of this protocol more freedom while
    // still meeting our requirements. For example, one
    // implementation might use Set<Node>.
    func neighbors(of node: Node) -> NodeSequence
}

57 Using first class functions when iterating over a dictionary

👨‍🍳 Combine first class functions in Swift with the fact that Dictionary elements are (Key, Value) tuples and you can build yourself some pretty awesome functional chains when iterating over a Dictionary.

func makeActor(at coordinate: Coordinate, for building: Building) -> Actor {
    let actor = Actor()
    actor.position = coordinate.point
    actor.animation = building.animation
    return actor
}

func render(_ buildings: [Coordinate : Building]) {
    buildings.map(makeActor).forEach(add)
}

56 Calling instance methods as static functions

😎 In Swift, you can call any instance method as a static function and it will return a closure representing that method. This is how running tests using SPM on Linux works.

More about this topic in my blog post "First class functions in Swift".

// This produces a '() -> Void' closure which is a reference to the
// given view's 'removeFromSuperview' method.
let closure = UIView.removeFromSuperview(view)

// We can now call it just like we would any other closure, and it
// will run 'view.removeFromSuperview()'
closure()

// This is how running tests using the Swift Package Manager on Linux
// works, you return your test functions as closures:
extension UserManagerTests {
    static var allTests = [
        ("testLoggingIn", testLoggingIn),
        ("testLoggingOut", testLoggingOut),
        ("testUserPermissions", testUserPermissions)
    ]
}

55 Dropping suffixes from method names to support multiple arguments

👏 One really nice benefit of dropping suffixes from method names (and just using verbs, when possible) is that it becomes super easy to support both single and multiple arguments, and it works really well semantically.

extension UIView {
    func add(_ subviews: UIView...) {
        subviews.forEach(addSubview)
    }
}

view.add(button)
view.add(label)

// By dropping the "Subview" suffix from the method name, both
// single and multiple arguments work really well semantically.
view.add(button, label)

54 Constraining protocols to classes to ensure mutability

👽 Using the AnyObject (or class) constraint on protocols is not only useful when defining delegates (or other weak references), but also when you always want instances to be mutable without copying.

// By constraining a protocol with 'AnyObject' it can only be adopted
// by classes, which means all instances will always be mutable, and
// that it's the original instance (not a copy) that will be mutated.
protocol DataContainer: AnyObject {
    var data: Data? { get set }
}

class UserSettingsManager {
    private var settings: Settings
    private let dataContainer: DataContainer

    // Since DataContainer is a protocol, we an easily mock it in
    // tests if we use dependency injection
    init(settings: Settings, dataContainer: DataContainer) {
        self.settings = settings
        self.dataContainer = dataContainer
    }

    func saveSettings() throws {
        let data = try settings.serialize()

        // We can now assign properties on an instance of our protocol
        // because the compiler knows it's always going to be a class
        dataContainer.data = data
    }
}

53 String-based enums in string interpolation

🍣 Even if you define a custom raw value for a string-based enum in Swift, the full case name will be used in string interpolation.

Super useful when using separate raw values for JSON, while still wanting to use the full case name in other contexts.

extension Building {
    // This enum has custom raw values that are used when decoding
    // a value, for example from JSON.
    enum Kind: String {
        case castle = "C"
        case town = "T"
        case barracks = "B"
        case goldMine = "G"
        case camp = "CA"
        case blacksmith = "BL"
    }

    var animation: Animation {
        return Animation(
            // When used in string interpolation, the full case name is still used.
            // For 'castle' this will be 'buildings/castle'.
            name: "buildings/\(kind)",
            frameCount: frameCount,
            frameDuration: frameDuration
        )
    }
}

52 Expressively comparing a value with a list of candidates

👨‍🔬 Continuing to experiment with expressive ways of comparing a value with a list of candidates in Swift. Adding an extension on Equatable is probably my favorite approach so far.

extension Equatable {
    func isAny(of candidates: Self...) -> Bool {
        return candidates.contains(self)
    }
}

let isHorizontal = direction.isAny(of: .left, .right)

See tip 35 for my previous experiment.

51 UIView bounds and transforms

📐 A really interesting side-effect of a UIView's bounds being its rect within its own coordinate system is that transforms don't affect it at all. That's why it's usually a better fit than frame when doing layout calculations of subviews.

let view = UIView()
view.frame.size = CGSize(width: 100, height: 100)
view.transform = CGAffineTransform(scaleX: 2, y: 2)

print(view.frame) // (-50.0, -50.0, 200.0, 200.0)
print(view.bounds) // (0.0, 0.0, 100.0, 100.0)

50 UIKit default arguments

👏 It's awesome that many UIKit APIs with completion handlers and other optional parameters import into Swift with default arguments (even though they are written in Objective-C). Getting rid of all those nil arguments is so nice!

// BEFORE: All parameters are specified, just like in Objective-C

viewController.present(modalViewController, animated: true, completion: nil)

modalViewController.dismiss(animated: true, completion: nil)

viewController.transition(from: loadingViewController,
                          to: contentViewController,
                          duration: 0.3,
                          options: [],
                          animations: animations,
                          completion: nil)

// AFTER: Since many UIKit APIs with completion handlers and other
// optional parameters import into Swift with default arguments,
// we can make our calls shorter

viewController.present(modalViewController, animated: true)

modalViewController.dismiss(animated: true)

viewController.transition(from: loadingViewController,
                          to: contentViewController,
                          duration: 0.3,
                          animations: animations)

49 Avoiding Massive View Controllers

✂️ Avoiding Massive View Controllers is all about finding the right levels of abstraction and splitting things up.

My personal rule of thumb is that as soon as I have 3 methods or properties that have the same prefix, I break them out into their own type.

// BEFORE

class LoginViewController: UIViewController {
    private lazy var signUpLabel = UILabel()
    private lazy var signUpImageView = UIImageView()
    private lazy var signUpButton = UIButton()
}

// AFTER

class LoginViewController: UIViewController {
    private lazy var signUpView = SignUpView()
}

class SignUpView: UIView {
    private lazy var label = UILabel()
    private lazy var imageView = UIImageView()
    private lazy var button = UIButton()
}

48 Extending optionals

❤️ I love the fact that optionals are enums in Swift - it makes it so easy to extend them with convenience APIs for certain types. Especially useful when doing things like data validation on optional values.

func validateTextFields() -> Bool {
    guard !usernameTextField.text.isNilOrEmpty else {
        return false
    }

    ...

    return true
}

// Since all optionals are actual enum values in Swift, we can easily
// extend them for certain types, to add our own convenience APIs

extension Optional where Wrapped == String {
    var isNilOrEmpty: Bool {
        switch self {
        case let string?:
            return string.isEmpty
        case nil:
            return true
        }
    }
}

// Since strings are now Collections in Swift 4, you can even
// add this property to all optional collections:

extension Optional where Wrapped: Collection {
    var isNilOrEmpty: Bool {
        switch self {
        case let collection?:
            return collection.isEmpty
        case nil:
            return true
        }
    }
}

47 Using where with for-loops

🗺 Using the where keyword can be a super nice way to quickly apply a filter in a for-loop in Swift. You can of course use map, filter and forEach, or guard, but for simple loops I think this is very expressive and nice.

func archiveMarkedPosts() {
    for post in posts where post.isMarked {
        archive(post)
    }
}

func healAllies() {
    for player in players where player.isAllied(to: currentPlayer) {
        player.heal()
    }
}

46 Variable shadowing

👻 Variable shadowing can be super useful in Swift, especially when you want to create a local copy of a parameter value in order to use it as state within a closure.

init(repeatMode: RepeatMode, closure: @escaping () -> UpdateOutcome) {
    // Shadow the argument with a local, mutable copy
    var repeatMode = repeatMode
    
    self.closure = {
        // With shadowing, there's no risk of accidentially
        // referring to the immutable version
        switch repeatMode {
        case .forever:
            break
        case .times(let count):
            guard count > 0 else {
                return .finished
            }
            
            // We can now capture the mutable version and use
            // it for state in a closure
            repeatMode = .times(count - 1)
        }
        
        return closure()
    }
}

45 Using dot syntax for static properties and initializers

✒️ Dot syntax is one of my favorite features of Swift. What's really cool is that it's not only for enums, any static method or property can be used with dot syntax - even initializers! Perfect for convenience APIs and default parameters.

public enum RepeatMode {
    case times(Int)
    case forever
}

public extension RepeatMode {
    static var never: RepeatMode {
        return .times(0)
    }

    static var once: RepeatMode {
        return .times(1)
    }
}

view.perform(animation, repeated: .once)

// To make default parameters more compact, you can even use init with dot syntax

class ImageLoader {
    init(cache: Cache = .init(), decoder: ImageDecoder = .init()) {
        ...
    }
}

44 Calling functions as closures with a tuple as parameters

🚀 One really cool aspect of Swift having first class functions is that you can pass any function (or even initializer) as a closure, and even call it with a tuple containing its parameters!

// This function lets us treat any "normal" function or method as
// a closure and run it with a tuple that contains its parameters
func call<Input, Output>(_ function: (Input) -> Output, with input: Input) -> Output {
    return function(input)
}

class ViewFactory {
    func makeHeaderView() -> HeaderView {
        // We can now pass an initializer as a closure, and a tuple
        // containing its parameters
        return call(HeaderView.init, with: loadTextStyles())
    }
    
    private func loadTextStyles() -> (font: UIFont, color: UIColor) {
        return (theme.font, theme.textColor)
    }
}

class HeaderView {
    init(font: UIFont, textColor: UIColor) {
        ...
    }
}

43 Enabling static dependency injection

💉 If you've been struggling to test code that uses static APIs, here's a technique you can use to enable static dependency injection without having to modify any call sites:

// Before: Almost impossible to test due to the use of singletons

class Analytics {
    static func log(_ event: Event) {
        Database.shared.save(event)
        
        let dictionary = event.serialize()
        NetworkManager.shared.post(dictionary, to: eventURL)
    }
}

// After: Much easier to test, since we can inject mocks as arguments

class Analytics {
    static func log(_ event: Event,
                    database: Database = .shared,
                    networkManager: NetworkManager = .shared) {
        database.save(event)
        
        let dictionary = event.serialize()
        networkManager.post(dictionary, to: eventURL)
    }
}

42 Type inference for lazy properties in Swift 4

🎉 In Swift 4, type inference works for lazy properties and you don't need to explicitly refer to self!

// Swift 3

class PurchaseView: UIView {
    private lazy var buyButton: UIButton = self.makeBuyButton()
    
    private func makeBuyButton() -> UIButton {
        let button = UIButton()
        button.setTitle("Buy", for: .normal)
        button.setTitleColor(.blue, for: .normal)
        return button
    }
}

// Swift 4

class PurchaseView: UIView {
    private lazy var buyButton = makeBuyButton()
    
    private func makeBuyButton() -> UIButton {
        let button = UIButton()
        button.setTitle("Buy", for: .normal)
        button.setTitleColor(.blue, for: .normal)
        return button
    }
}

41 Converting Swift errors to NSError

😎 You can turn any Swift Error into an NSError, which is super useful when pattern matching with a code 👍. Also, switching on optionals is pretty cool!

let task = urlSession.dataTask(with: url) { data, _, error in
    switch error {
    case .some(let error as NSError) where error.code == NSURLErrorNotConnectedToInternet:
        presenter.showOfflineView()
    case .some(let error):
        presenter.showGenericErrorView()
    case .none:
        presenter.renderContent(from: data)
    }
}

task.resume()

Also make sure to check out Kostas Kremizas' tip about how you can pattern match directly against a member of URLError.

40 Making UIImage macOS compatible

🖥 Here's an easy way to make iOS model code that uses UIImage macOS compatible - like me and Gui Rambo discussed on the Swift by Sundell Podcast.

// Either put this in a separate file that you only include in your macOS target or wrap the code in #if os(macOS) / #endif

import Cocoa

// Step 1: Typealias UIImage to NSImage
typealias UIImage = NSImage

// Step 2: You might want to add these APIs that UIImage has but NSImage doesn't.
extension NSImage {
    var cgImage: CGImage? {
        var proposedRect = CGRect(origin: .zero, size: size)

        return cgImage(forProposedRect: &proposedRect,
                       context: nil,
                       hints: nil)
    }

    convenience init?(named name: String) {
        self.init(named: Name(name))
    }
}

// Step 3: Profit - you can now make your model code that uses UIImage cross-platform!
struct User {
    let name: String
    let profileImage: UIImage
}

39 Internally mutable protocol-oriented APIs

🤖 You can easily define a protocol-oriented API that can only be mutated internally, by using an internal protocol that extends a public one.

// Declare a public protocol that acts as your immutable API
public protocol ModelHolder {
    associatedtype Model
    var model: Model { get }
}

// Declare an extended, internal protocol that provides a mutable API
internal protocol MutableModelHolder: ModelHolder {
    var model: Model { get set }
}

// You can now implement the requirements using 'public internal(set)'
public class UserHolder: MutableModelHolder {
    public internal(set) var model: User

    internal init(model: User) {
        self.model = model
    }
}

38 Switching on a set

🎛 You can switch on a set using array literals as cases in Swift! Can be really useful to avoid many if/else if statements.

class RoadTile: Tile {
    var connectedDirections = Set<Direction>()

    func render() {
        switch connectedDirections {
        case [.up, .down]:
            image = UIImage(named: "road-vertical")
        case [.left, .right]:
            image = UIImage(named: "road-horizontal")
        default:
            image = UIImage(named: "road")
        }
    }
}

37 Adding the current locale to cache keys

🌍 When caching localized content in an app, it's a good idea to add the current locale to all keys, to prevent bugs when switching languages.

func cache(_ content: Content, forKey key: String) throws {
    let data = try wrap(content) as Data
    let key = localize(key: key)
    try storage.store(data, forKey: key)
}

func loadCachedContent(forKey key: String) -> Content? {
    let key = localize(key: key)
    let data = storage.loadData(forKey: key)
    return data.flatMap { try? unbox(data: $0) }
}

private func localize(key: String) -> String {
    return key + "-" + Bundle.main.preferredLocalizations[0]
}

36 Setting up tests to avoid retain cycles with weak references

🚳 Here's an easy way to setup a test to avoid accidental retain cycles with object relationships (like weak delegates & observers) in Swift:

func testDelegateNotRetained() {
    // Assign the delegate (weak) and also retain it using a local var
    var delegate: Delegate? = DelegateMock()
    controller.delegate = delegate
    XCTAssertNotNil(controller.delegate)
    
    // Release the local var, which should also release the weak reference
    delegate = nil
    XCTAssertNil(controller.delegate)
}

35 Expressively matching a value against a list of candidates

👨‍🔬 Playing around with an expressive way to check if a value matches any of a list of candidates in Swift:

// Instead of multiple conditions like this:

if string == "One" || string == "Two" || string == "Three" {

}

// You can now do:

if string == any(of: "One", "Two", "Three") {

}

You can find a gist with the implementation here.

34 Organizing code using extensions

👪 APIs in a Swift extension automatically inherit its access control level, making it a neat way to organize public, internal & private APIs.

public extension Animation {
    init(textureNamed textureName: String) {
        frames = [Texture(name: textureName)]
    }
    
    init(texturesNamed textureNames: [String], frameDuration: TimeInterval = 1) {
        frames = textureNames.map(Texture.init)
        self.frameDuration = frameDuration
    }
    
    init(image: Image) {
        frames = [Texture(image: image)]
    }
}

internal extension Animation {
    func loadFrameImages() -> [Image] {
        return frames.map { $0.loadImageIfNeeded() }
    }
}

33 Using map to transform an optional into a Result type

🗺 Using map you can transform an optional value into an optional Result type by simply passing in the enum case.

enum Result<Value> {
    case value(Value)
    case error(Error)
}

class Promise<Value> {
    private var result: Result<Value>?
    
    init(value: Value? = nil) {
        result = value.map(Result.value)
    }
}

32 Assigning to self in struct initializers

👌 It's so nice that you can assign directly to self in struct initializers in Swift. Very useful when adding conformance to protocols.

extension Bool: AnswerConvertible {
    public init(input: String) throws {
        switch input.lowercased() {
        case "y", "yes", "👍":
            self = true
        default:
            self = false
        }
    }
}

31 Recursively calling closures as inline functions

☎️ Defining Swift closures as inline functions enables you to recursively call them, which is super useful in things like custom sequences.

class Database {
    func records(matching query: Query) -> AnySequence<Record> {
        var recordIterator = loadRecords().makeIterator()
        
        func iterate() -> Record? {
            guard let nextRecord = recordIterator.next() else {
                return nil
            }
            
            guard nextRecord.matches(query) else {
                // Since the closure is an inline function, it can be recursively called,
                // in this case in order to advance to the next item.
                return iterate()
            }
            
            return nextRecord
        }
        
        // AnySequence/AnyIterator are part of the standard library and provide an easy way
        // to define custom sequences using closures.
        return AnySequence { AnyIterator(iterate) }
    }
}

Rob Napier points out that using the above might cause crashes if used on a large databaset, since Swift has no guaranteed Tail Call Optimization (TCO).

Slava Pestov also points out that another benefit of inline functions vs closures is that they can have their own generic parameter list.

30 Passing self to required Objective-C dependencies

🏖 Using lazy properties in Swift, you can pass self to required Objective-C dependencies without having to use force-unwrapped optionals.

class DataLoader: NSObject {
    lazy var urlSession: URLSession = self.makeURLSession()
    
    private func makeURLSession() -> URLSession {
        return URLSession(configuration: .default, delegate: self, delegateQueue: .main)
    }
}

class Renderer {
    lazy var displayLink: CADisplayLink = self.makeDisplayLink()
    
    private func makeDisplayLink() -> CADisplayLink {
        return CADisplayLink(target: self, selector: #selector(screenDidRefresh))
    }
}

29 Making weak or lazy properties readonly

👓 If you have a property in Swift that needs to be weak or lazy, you can still make it readonly by using private(set).

class Node {
    private(set) weak var parent: Node?
    private(set) lazy var children = [Node]()

    func add(child: Node) {
        children.append(child)
        child.parent = self
    }
}

28 Defining static URLs using string literals

🌏 Tired of using URL(string: "url")! for static URLs? Make URL conform to ExpressibleByStringLiteral and you can now simply use "url" instead.

extension URL: ExpressibleByStringLiteral {
    // By using 'StaticString' we disable string interpolation, for safety
    public init(stringLiteral value: StaticString) {
        self = URL(string: "\(value)").require(hint: "Invalid URL string literal: \(value)")
    }
}

// We can now define URLs using static string literals 🎉
let url: URL = "https://www.swiftbysundell.com"
let task = URLSession.shared.dataTask(with: "https://www.swiftbysundell.com")

// In Swift 3 or earlier, you also have to implement 2 additional initializers
extension URL {
    public init(extendedGraphemeClusterLiteral value: StaticString) {
        self.init(stringLiteral: value)
    }

    public init(unicodeScalarLiteral value: StaticString) {
        self.init(stringLiteral: value)
    }
}

To find the extension that adds the require() method on Optional that I use above, check out Require.

27 Manipulating points, sizes and frames using math operators

✚ I'm always careful with operator overloading, but for manipulating things like sizes, points & frames I find them super useful.

extension CGSize {
    static func *(lhs: CGSize, rhs: CGFloat) -> CGSize {
        return CGSize(width: lhs.width * rhs, height: lhs.height * rhs)
    }
}

button.frame.size = image.size * 2

If you like the above idea, check out CGOperators, which contains math operator overloads for all Core Graphics' vector types.

26 Using closure types in generic constraints

🔗 You can use closure types in generic constraints in Swift. Enables nice APIs for handling sequences of closures.

extension Sequence where Element == () -> Void {
    func callAll() {
        forEach { $0() }
    }
}

extension Sequence where Element == () -> String {
    func joinedResults(separator: String) -> String {
        return map { $0() }.joined(separator: separator)
    }
}

callbacks.callAll()
let names = nameProviders.joinedResults(separator: ", ")

(If you're using Swift 3, you have to change Element to Iterator.Element)

25 Using associated enum values to avoid state-specific optionals

🎉 Using associated enum values is a super nice way to encapsulate mutually exclusive state info (and avoiding state-specific optionals).

// BEFORE: Lots of state-specific, optional properties

class Player {
    var isWaitingForMatchMaking: Bool
    var invitingUser: User?
    var numberOfLives: Int
    var playerDefeatedBy: Player?
    var roundDefeatedIn: Int?
}

// AFTER: All state-specific information is encapsulated in enum cases

class Player {
    enum State {
        case waitingForMatchMaking
        case waitingForInviteResponse(from: User)
        case active(numberOfLives: Int)
        case defeated(by: Player, roundNumber: Int)
    }
    
    var state: State
}

24 Using enums for async result types

👍 I really like using enums for all async result types, even boolean ones. Self-documenting, and makes the call site a lot nicer to read too!

protocol PushNotificationService {
    // Before
    func enablePushNotifications(completionHandler: @escaping (Bool) -> Void)
    
    // After
    func enablePushNotifications(completionHandler: @escaping (PushNotificationStatus) -> Void)
}

enum PushNotificationStatus {
    case enabled
    case disabled
}

service.enablePushNotifications { status in
    if status == .enabled {
        enableNotificationsButton.removeFromSuperview()
    }
}

23 Working on async code in a playground

🏃 Want to work on your async code in a Swift Playground? Just set needsIndefiniteExecution to true to keep it running:

import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

DispatchQueue.main.asyncAfter(deadline: .now() + 3) {
    let greeting = "Hello after 3 seconds"
    print(greeting)
}

To stop the playground from executing, simply call PlaygroundPage.current.finishExecution().

22 Overriding self with a weak reference

💦 Avoid memory leaks when accidentially refering to self in closures by overriding it locally with a weak reference:

Swift >= 4.2

dataLoader.loadData(from: url) { [weak self] result in
    guard let self = self else { 
        return 
    }

    self.cache(result)
    
    ...

Swift < 4.2

dataLoader.loadData(from: url) { [weak self] result in
    guard let `self` = self else {
        return
    }

    self.cache(result)
    
    ...

Note that the reason the above currently works is because of a compiler bug (which I hope gets turned into a properly supported feature soon).

21 Using DispatchWorkItem

🕓 Using dispatch work items you can easily cancel a delayed asynchronous GCD task if you no longer need it:

let workItem = DispatchWorkItem {
    // Your async code goes in here
}

// Execute the work item after 1 second
DispatchQueue.main.asyncAfter(deadline: .now() + 1, execute: workItem)

// You can cancel the work item if you no longer need it
workItem.cancel()

20 Combining a sequence of functions

➕ While working on a new Swift developer tool (to be open sourced soon 😉), I came up with a pretty neat way of organizing its sequence of operations, by combining their functions into a closure:

internal func +<A, B, C>(lhs: @escaping (A) throws -> B,
                         rhs: @escaping (B) throws -> C) -> (A) throws -> C {
    return { try rhs(lhs($0)) }
}

public func run() throws {
    try (determineTarget + build + analyze + output)()
}

If you're familiar with the functional programming world, you might know the above technique as the pipe operator (thanks to Alexey Demedreckiy for pointing this out!)

19 Chaining optionals with map() and flatMap()

🗺 Using map() and flatMap() on optionals you can chain multiple operations without having to use lengthy if lets or guards:

// BEFORE

guard let string = argument(at: 1) else {
    return
}

guard let url = URL(string: string) else {
    return
}

handle(url)

// AFTER

argument(at: 1).flatMap(URL.init).map(handle)

18 Using self-executing closures for lazy properties

🚀 Using self-executing closures is a great way to encapsulate lazy property initialization:

class StoreViewController: UIViewController {
    private lazy var collectionView: UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        let view = UICollectionView(frame: self.view.bounds, collectionViewLayout: layout)
        view.delegate = self
        view.dataSource = self
        return view
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(collectionView)
    }
}

17 Speeding up Swift package tests

⚡️ You can speed up your Swift package tests using the --parallel flag. For Marathon, the tests execute 3 times faster that way!

swift test --parallel

16 Avoiding mocking UserDefaults

🛠 Struggling with mocking UserDefaults in a test? The good news is: you don't need mocking - just create a real instance:

class LoginTests: XCTestCase {
    private var userDefaults: UserDefaults!
    private var manager: LoginManager!
    
    override func setUp() {
        super.setup()
        
        userDefaults = UserDefaults(suiteName: #file)
        userDefaults.removePersistentDomain(forName: #file)
        
        manager = LoginManager(userDefaults: userDefaults)
    }
}

15 Using variadic parameters

👍 Using variadic parameters in Swift, you can create some really nice APIs that take a list of objects without having to use an array:

extension Canvas {
    func add(_ shapes: Shape...) {
        shapes.forEach(add)
    }
}

let circle = Circle(center: CGPoint(x: 5, y: 5), radius: 5)
let lineA = Line(start: .zero, end: CGPoint(x: 10, y: 10))
let lineB = Line(start: CGPoint(x: 0, y: 10), end: CGPoint(x: 10, y: 0))

let canvas = Canvas()
canvas.add(circle, lineA, lineB)
canvas.render()

14 Referring to enum cases with associated values as closures

😮 Just like you can refer to a Swift function as a closure, you can do the same thing with enum cases with associated values:

enum UnboxPath {
    case key(String)
    case keyPath(String)
}

struct UserSchema {
    static let name = key("name")
    static let age = key("age")
    static let posts = key("posts")
    
    private static let key = UnboxPath.key
}

13 Using the === operator to compare objects by instance

📈 The === operator lets you check if two objects are the same instance. Very useful when verifying that an array contains an instance in a test:

protocol InstanceEquatable: class, Equatable {}

extension InstanceEquatable {
    static func ==(lhs: Self, rhs: Self) -> Bool {
        return lhs === rhs
    }
}

extension Enemy: InstanceEquatable {}

func testDestroyingEnemy() {
    player.attack(enemy)
    XCTAssertTrue(player.destroyedEnemies.contains(enemy))
}

12 Calling initializers with dot syntax and passing them as closures

😎 Cool thing about Swift initializers: you can call them using dot syntax and pass them as closures! Perfect for mocking dates in tests.

class Logger {
    private let storage: LogStorage
    private let dateProvider: () -> Date
    
    init(storage: LogStorage = .init(), dateProvider: @escaping () -> Date = Date.init) {
        self.storage = storage
        self.dateProvider = dateProvider
    }
    
    func log(event: Event) {
        storage.store(event: event, date: dateProvider())
    }
}

11 Structuring UI tests as extensions on XCUIApplication

📱 Most of my UI testing logic is now categories on XCUIApplication. Makes the test cases really easy to read:

func testLoggingInAndOut() {
    XCTAssertFalse(app.userIsLoggedIn)
    
    app.launch()
    app.login()
    XCTAssertTrue(app.userIsLoggedIn)
    
    app.logout()
    XCTAssertFalse(app.userIsLoggedIn)
}

func testDisplayingCategories() {
    XCTAssertFalse(app.isDisplayingCategories)
    
    app.launch()
    app.login()
    app.goToCategories()
    XCTAssertTrue(app.isDisplayingCategories)
}

10 Avoiding default cases in switch statements

🙂 It’s a good idea to avoid “default” cases when switching on Swift enums - it’ll “force you” to update your logic when a new case is added:

enum State {
    case loggedIn
    case loggedOut
    case onboarding
}

func handle(_ state: State) {
    switch state {
    case .loggedIn:
        showMainUI()
    case .loggedOut:
        showLoginUI()
    // Compiler error: Switch must be exhaustive
    }
}

9 Using the guard statement in many different scopes

💂 It's really cool that you can use Swift's 'guard' statement to exit out of pretty much any scope, not only return from functions:

// You can use the 'guard' statement to...

for string in strings {
    // ...continue an iteration
    guard shouldProcess(string) else {
        continue
    }
    
    // ...or break it
    guard !shouldBreak(for: string) else {
        break
    }
    
    // ...or return
    guard !shouldReturn(for: string) else {
        return
    }
    
    // ..or throw an error
    guard string.isValid else {
        throw StringError.invalid(string)
    }
    
    // ...or exit the program
    guard !shouldExit(for: string) else {
        exit(1)
    }
}

8 Passing functions & operators as closures

❤️ Love how you can pass functions & operators as closures in Swift. For example, it makes the syntax for sorting arrays really nice!

let array = [3, 9, 1, 4, 6, 2]
let sorted = array.sorted(by: <)

7 Using #function for UserDefaults key consistency

🗝 Here's a neat little trick I use to get UserDefault key consistency in Swift (#function expands to the property name in getters/setters). Just remember to write a good suite of tests that'll guard you against bugs when changing property names.

extension UserDefaults {
    var onboardingCompleted: Bool {
        get { return bool(forKey: #function) }
        set { set(newValue, forKey: #function) }
    }
}

6 Using a name already taken by the standard library

📛 Want to use a name already taken by the standard library for a nested type? No problem - just use Swift. to disambiguate:

extension Command {
    enum Error: Swift.Error {
        case missing
        case invalid(String)
    }
}

5 Using Wrap to implement Equatable

📦 Playing around with using Wrap to implement Equatable for any type, primarily for testing:

protocol AutoEquatable: Equatable {}

extension AutoEquatable {
    static func ==(lhs: Self, rhs: Self) -> Bool {
        let lhsData = try! wrap(lhs) as Data
        let rhsData = try! wrap(rhs) as Data
        return lhsData == rhsData
    }
}

4 Using typealiases to reduce the length of method signatures

📏 One thing that I find really useful in Swift is to use typealiases to reduce the length of method signatures in generic types:

public class PathFinder<Object: PathFinderObject> {
    public typealias Map = Object.Map
    public typealias Node = Map.Node
    public typealias Path = PathFinderPath<Object>
    
    public static func possiblePaths(for object: Object, at rootNode: Node, on map: Map) -> Path.Sequence {
        return .init(object: object, rootNode: rootNode, map: map)
    }
}

3 Referencing either external or internal parameter name when writing docs

📖 You can reference either the external or internal parameter label when writing Swift docs - and they get parsed the same:

// EITHER:

class Foo {
    /**
    *   - parameter string: A string
    */
    func bar(with string: String) {}
}

// OR:

class Foo {
    /**
    *   - parameter with: A string
    */
    func bar(with string: String) {}
}

2 Using auto closures

👍 Finding more and more uses for auto closures in Swift. Can enable some pretty nice APIs:

extension Dictionary {
    mutating func value(for key: Key, orAdd valueClosure: @autoclosure () -> Value) -> Value {
        if let value = self[key] {
            return value
        }
        
        let value = valueClosure()
        self[key] = value
        return value
    }
}

1 Namespacing with nested types

🚀 I’ve started to become a really big fan of nested types in Swift. Love the additional namespacing it gives you!

public struct Map {
    public struct Model {
        public let size: Size
        public let theme: Theme
        public var terrain: [Position : Terrain.Model]
        public var units: [Position : Unit.Model]
        public var buildings: [Position : Building.Model]
    }
    
    public enum Direction {
        case up
        case right
        case down
        case left
    }
    
    public struct Position {
        public var x: Int
        public var y: Int
    }
    
    public enum Size: String {
        case small = "S"
        case medium = "M"
        case large = "L"
        case extraLarge = "XL"
    }
}

Download Details:

Author: JohnSundell
Source Code: https://github.com/JohnSundell/SwiftTips 
License: MIT license

#swift #tips #tricks 

A Collection Of Swift Tips & Tricks That I've Shared on Twitter

⚠️ This list is no longer being updated. For my latest Swift tips, checkout the "Tips" section on Swift by Sundell.

Swift tips & tricks ⚡️

One of the things I really love about Swift is how I keep finding interesting ways to use it in various situations, and when I do - I usually share them on Twitter. Here's a collection of all the tips & tricks that I've shared so far. Each entry has a link to the original tweet, if you want to respond with some feedback or question, which is always super welcome! 🚀

Also make sure to check out all of my other Swift content:

#102 Making async tests faster and more stable

🚀 Here are some quick tips to make async tests faster & more stable:

  • 😴 Avoid sleep() - use expectations instead
  • ⏱ Use generous timeouts to avoid flakiness on CI
  • 🧐 Put all assertions at the end of each test, not inside closures
// BEFORE:

class MentionDetectorTests: XCTestCase {
    func testDetectingMention() {
        let detector = MentionDetector()
        let string = "This test was written by @johnsundell."

        detector.detectMentions(in: string) { mentions in
            XCTAssertEqual(mentions, ["johnsundell"])
        }
        
        sleep(2)
    }
}

// AFTER:

class MentionDetectorTests: XCTestCase {
    func testDetectingMention() {
        let detector = MentionDetector()
        let string = "This test was written by @johnsundell."

        var mentions: [String]?
        let expectation = self.expectation(description: #function)

        detector.detectMentions(in: string) {
            mentions = $0
            expectation.fulfill()
        }

        waitForExpectations(timeout: 10)
        XCTAssertEqual(mentions, ["johnsundell"])
    }
}

For more on async testing, check out "Unit testing asynchronous Swift code".

#101 Adding support for Apple Pencil double-taps

✍️ Adding support for the new Apple Pencil double-tap feature is super easy! All you have to do is to create a UIPencilInteraction, add it to a view, and implement one delegate method. Hopefully all pencil-compatible apps will soon adopt this.

let interaction = UIPencilInteraction()
interaction.delegate = self
view.addInteraction(interaction)

extension ViewController: UIPencilInteractionDelegate {
    func pencilInteractionDidTap(_ interaction: UIPencilInteraction) {
        // Handle pencil double-tap
    }
}

For more on using this and other iPad Pro features, check out "Building iPad Pro features in Swift".

#100 Combining values with functions

😎 Here's a cool function that combines a value with a function to return a closure that captures that value, so that it can be called without any arguments. Super useful when working with closure-based APIs and we want to use some of our properties without having to capture self.

func combine<A, B>(_ value: A, with closure: @escaping (A) -> B) -> () -> B {
    return { closure(value) }
}

// BEFORE:

class ProductViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        buyButton.handler = { [weak self] in
            guard let self = self else {
                return
            }
            
            self.productManager.startCheckout(for: self.product)
        }
    }
}

// AFTER:

class ProductViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        buyButton.handler = combine(product, with: productManager.startCheckout)
    }
}

#99 Dependency injection using functions

💉 When I'm only using a single function from a dependency, I love to inject that function as a closure, instead of having to create a protocol and inject the whole object. Makes dependency injection & testing super simple.

final class ArticleLoader {
    typealias Networking = (Endpoint) -> Future<Data>
    
    private let networking: Networking
    
    init(networking: @escaping Networking = URLSession.shared.load) {
        self.networking = networking
    }
    
    func loadLatest() -> Future<[Article]> {
        return networking(.latestArticles).decode()
    }
}

For more on this technique, check out "Simple Swift dependency injection with functions".

#98 Using a custom exception handler

💥 It's cool that you can easily assign a closure as a custom NSException handler. This is super useful when building things in Playgrounds - since you can't use breakpoints - so instead of just signal SIGABRT, you'll get the full exception description if something goes wrong.

NSSetUncaughtExceptionHandler { exception in
    print(exception)
}

#97 Using type aliases to give semantic meaning to primitives

❤️ I love that in Swift, we can use the type system to make our code so much more self-documenting - one way of doing so is to use type aliases to give the primitive types that we use a more semantic meaning.

extension List.Item {
    // Using type aliases, we can give semantic meaning to the
    // primitive types that we use, without having to introduce
    // wrapper types.
    typealias Index = Int
}

extension List {
    enum Mutation {
        // Our enum cases now become a lot more self-documenting,
        // without having to add additional parameter labels to
        // explain them.
        case add(Item, Item.Index)
        case update(Item, Item.Index)
        case remove(Item.Index)
    }
}

For more on self-documenting code, check out "Writing self-documenting Swift code".

#96 Specializing protocols using constraints

🤯 A little late night prototyping session reveals that protocol constraints can not only be applied to extensions - they can also be added to protocol definitions!

This is awesome, since it lets us easily define specialized protocols based on more generic ones.

protocol Component {
    associatedtype Container
    func add(to container: Container)
}

// Protocols that inherit from other protocols can include
// constraints to further specialize them.
protocol ViewComponent: Component where Container == UIView {
    associatedtype View: UIView
    var view: View { get }
}

extension ViewComponent {
    func add(to container: UIView) {
        container.addSubview(view)
    }
}

For more on specializing protocols, check out "Specializing protocols in Swift".

#95 Unwrapping an optional or throwing an error

📦 Here's a super handy extension on Swift's Optional type, which gives us a really nice API for easily unwrapping an optional, or throwing an error in case the value turned out to be nil:

extension Optional {
    func orThrow(_ errorExpression: @autoclosure () -> Error) throws -> Wrapped {
        switch self {
        case .some(let value):
            return value
        case .none:
            throw errorExpression()
        }
    }
}

let file = try loadFile(at: path).orThrow(MissingFileError())

For more ways that optionals can be extended, check out "Extending optionals in Swift".

#94 Testing code that uses static APIs

👩‍🔬 Testing code that uses static APIs can be really tricky, but there's a way that it can often be done - using Swift's first class function capabilities!

Instead of accessing that static API directly, we can inject the function we want to use, which enables us to mock it!

// BEFORE

class FriendsLoader {
    func loadFriends(then handler: @escaping (Result<[Friend]>) -> Void) {
        Networking.loadData(from: .friends) { result in
            ...
        }
    }
}

// AFTER

class FriendsLoader {
    typealias Handler<T> = (Result<T>) -> Void
    typealias DataLoadingFunction = (Endpoint, @escaping Handler<Data>) -> Void

    func loadFriends(using dataLoading: DataLoadingFunction = Networking.loadData,
                     then handler: @escaping Handler<[Friend]>) {
        dataLoading(.friends) { result in
            ...
        }
    }
}

// MOCKING IN TESTS

let dataLoading: FriendsLoader.DataLoadingFunction = { _, handler in
    handler(.success(mockData))
}

friendsLoader.loadFriends(using: dataLoading) { result in
    ...
}

#93 Matching multiple enum cases with associated values

🐾 Swift's pattern matching capabilities are so powerful! Two enum cases with associated values can even be matched and handled by the same switch case - which is super useful when handling state changes with similar data.

enum DownloadState {
    case inProgress(progress: Double)
    case paused(progress: Double)
    case cancelled
    case finished(Data)
}

func downloadStateDidChange(to state: DownloadState) {
    switch state {
    case .inProgress(let progress), .paused(let progress):
        updateProgressView(with: progress)
    case .cancelled:
        showCancelledMessage()
    case .finished(let data):
        process(data)
    }
}

#92 Multiline string literals

🅰 One really nice benefit of Swift multiline string literals - even for single lines of text - is that they don't require quotes to be escaped. Perfect when working with things like HTML, or creating a custom description for an object.

let html = highlighter.highlight("Array<String>")

XCTAssertEqual(html, """
<span class="type">Array</span>&lt;<span class="type">String</span>&gt;
""")

#91 Reducing sequences

💎 While it's very common in functional programming, the reduce function might be a bit of a hidden gem in Swift. It provides a super useful way to transform a sequence into a single value.

extension Sequence where Element: Equatable {
    func numberOfOccurrences(of target: Element) -> Int {
        return reduce(0) { result, element in
            guard element == target else {
                return result
            }

            return result + 1
        }
    }
}

You can read more about transforming collections in "Transforming collections in Swift".

#90 Avoiding manual Codable implementations

📦 When I use Codable in Swift, I want to avoid manual implementations as much as possible, even when there's a mismatch between my code structure and the JSON I'm decoding.

One way that can often be achieved is to use private data containers combined with computed properties.

struct User: Codable {
    let name: String
    let age: Int

    var homeTown: String { return originPlace.name }

    private let originPlace: Place
}

private extension User {
    struct Place: Codable {
        let name: String
    }
}

extension User {
    struct Container: Codable {
        let user: User
    }
}

#89 Using feature flags instead of feature branches

🚢 Instead of using feature branches, I merge almost all of my code directly into master - and then I use feature flags to conditionally enable features when they're ready. That way I can avoid merge conflicts and keep shipping!

extension ListViewController {
    func addSearchIfNeeded() {
        // Rather than having to keep maintaining a separate
        // feature branch for a new feature, we can use a flag
        // to conditionally turn it on.
        guard FeatureFlags.searchEnabled else {
            return
        }

        let resultsVC = SearchResultsViewController()
        let searchVC = UISearchController(
            searchResultsController: resultsVC
        )

        searchVC.searchResultsUpdater = resultsVC
        navigationItem.searchController = searchVC
    }
}

You can read more about feature flags in "Feature flags in Swift".

#88 Lightweight data hierarchies using tuples

💾 Here I'm using tuples to create a lightweight hierarchy for my data, giving me a nice structure without having to introduce any additional types.

struct CodeSegment {
    var tokens: (
        previous: String?,
        current: String
    )

    var delimiters: (
        previous: Character?
        next: Character?
    )
}

handle(segment.tokens.current)

You can read more about tuples in "Using tuples as lightweight types in Swift"

#87 The rule of threes

3️⃣ Whenever I have 3 properties or local variables that share the same prefix, I usually try to extract them into their own method or type. That way I can avoid massive types & methods, and also increase readability, without falling into a "premature optimization" trap.

Before

public func generate() throws {
    let contentFolder = try folder.subfolder(named: "content")

    let articleFolder = try contentFolder.subfolder(named: "posts")
    let articleProcessor = ContentProcessor(folder: articleFolder)
    let articles = try articleProcessor.process()

    ...
}

After

public func generate() throws {
    let contentFolder = try folder.subfolder(named: "content")
    let articles = try processArticles(in: contentFolder)
    ...
}

private func processArticles(in folder: Folder) throws -> [ContentItem] {
    let folder = try folder.subfolder(named: "posts")
    let processor = ContentProcessor(folder: folder)
    return try processor.process()
}

#86 Useful Codable extensions

👨‍🔧 Here's two extensions that I always add to the Encodable & Decodable protocols, which for me really make the Codable API nicer to use. By using type inference for decoding, a lot of boilerplate can be removed when the compiler is already able to infer the resulting type.

extension Encodable {
    func encoded() throws -> Data {
        return try JSONEncoder().encode(self)
    }
}

extension Data {
    func decoded<T: Decodable>() throws -> T {
        return try JSONDecoder().decode(T.self, from: self)
    }
}

let data = try user.encoded()

// By using a generic type in the decoded() method, the
// compiler can often infer the type we want to decode
// from the current context.
try userDidLogin(data.decoded())

// And if not, we can always supply the type, still making
// the call site read very nicely.
let otherUser = try data.decoded() as User

#85 Using shared UserDefaults suites

📦 UserDefaults is a lot more powerful than what it first might seem like. Not only can it store more complex values (like dates & dictionaries) and parse command line arguments - it also enables easy sharing of settings & lightweight data between apps in the same App Group.

let sharedDefaults = UserDefaults(suiteName: "my-app-group")!
let useDarkMode = sharedDefaults.bool(forKey: "dark-mode")

// This value is put into the shared suite.
sharedDefaults.set(true, forKey: "dark-mode")

// If you want to treat the shared settings as read-only (and add
// local overrides on top of them), you can simply add the shared
// suite to the standard UserDefaults.
let combinedDefaults = UserDefaults.standard
combinedDefaults.addSuite(named: "my-app-group")

// This value is a local override, not added to the shared suite.
combinedDefaults.set(true, forKey: "app-specific-override")

#84 Custom UIView backing layers

🎨 By overriding layerClass you can tell UIKit what CALayer class to use for a UIView's backing layer. That way you can reduce the amount of layers, and don't have to do any manual layout.

final class GradientView: UIView {
    override class var layerClass: AnyClass { return CAGradientLayer.self }

    var colors: (start: UIColor, end: UIColor)? {
        didSet { updateLayer() }
    }

    private func updateLayer() {
        let layer = self.layer as! CAGradientLayer
        layer.colors = colors.map { [$0.start.cgColor, $0.end.cgColor] }
    }
}

#83 Auto-Equatable enums with associated values

✅ That the compiler now automatically synthesizes Equatable conformances is such a huge upgrade for Swift! And the cool thing is that it works for all kinds of types - even for enums with associated values! Especially useful when using enums for verification in unit tests.

struct Article: Equatable {
    let title: String
    let text: String
}

struct User: Equatable {
    let name: String
    let age: Int
}

extension Navigator {
    enum Destination: Equatable {
        case profile(User)
        case article(Article)
    }
}

func testNavigatingToArticle() {
    let article = Article(title: "Title", text: "Text")
    controller.select(article)
    XCTAssertEqual(navigator.destinations, [.article(article)])
}

#82 Defaults for associated types

🤝 Associated types can have defaults in Swift - which is super useful for types that are not easily inferred (for example when they're not used for a specific instance method or property).

protocol Identifiable {
    associatedtype RawIdentifier: Codable = String

    var id: Identifier<Self> { get }
}

struct User: Identifiable {
    let id: Identifier<User>
    let name: String
}

struct Group: Identifiable {
    typealias RawIdentifier = Int

    let id: Identifier<Group>
    let name: String
}

#81 Creating a dedicated identifier type

🆔 If you want to avoid using plain strings as identifiers (which can increase both type safety & readability), it's really easy to create a custom Identifier type that feels just like a native Swift type, thanks to protocols!

More on this topic in "Type-safe identifiers in Swift".

struct Identifier: Hashable {
    let string: String
}

extension Identifier: ExpressibleByStringLiteral {
    init(stringLiteral value: String) {
        string = value
    }
}

extension Identifier: CustomStringConvertible {
    var description: String {
        return string
    }
}

extension Identifier: Codable {
    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        string = try container.decode(String.self)
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        try container.encode(string)
    }
}

struct Article: Codable {
    let id: Identifier
    let title: String
}

let article = Article(id: "my-article", title: "Hello world!")

#80 Assigning optional tuple members to variables

🙌 A really cool thing about using tuples to model the internal state of a Swift type, is that you can unwrap an optional tuple's members directly into local variables.

Very useful in order to group multiple optional values together for easy unwrapping & handling.

class ImageTransformer {
    private var queue = [(image: UIImage, transform: Transform)]()

    private func processNext() {
        // When unwrapping an optional tuple, you can assign the members
        // directly to local variables.
        guard let (image, transform) = queue.first else {
            return
        }

        let context = Context()
        context.draw(image)
        context.apply(transform)
        ...
    }
}

#79 Struct convenience initializers

❤️ I love to structure my code using extensions in Swift. One big benefit of doing so when it comes to struct initializers, is that defining a convenience initializer doesn't remove the default one the compiler generates - best of both worlds!

struct Article {
    let date: Date
    var title: String
    var text: String
    var comments: [Comment]
}

extension Article {
    init(title: String, text: String) {
        self.init(date: Date(), title: title, text: text, comments: [])
    }
}

let articleA = Article(title: "Best Cupcake Recipe", text: "...")

let articleB = Article(
    date: Date(),
    title: "Best Cupcake Recipe",
    text: "...",
    comments: [
        Comment(user: currentUser, text: "Yep, can confirm!")
    ]
)

#78 Usages of throwing functions

🏈 A big benefit of using throwing functions for synchronous Swift APIs is that the caller can decide whether they want to treat the return value as optional (try?) or required (try).

func loadFile(named name: String) throws -> File {
    guard let url = urlForFile(named: name) else {
        throw File.Error.missing
    }

    do {
        let data = try Data(contentsOf: url)
        return File(url: url, data: data)
    } catch {
        throw File.Error.invalidData(error)
    }
}

let requiredFile = try loadFile(named: "AppConfig.json")

let optionalFile = try? loadFile(named: "UserSettings.json")

#77 Nested generic types

🐝 Types that are nested in generics automatically inherit their parent's generic types - which is super useful when defining accessory types (for things like states or outcomes).

struct Task<Input, Output> {
    typealias Closure = (Input) throws -> Output

    let closure: Closure
}

extension Task {
    enum Result {
        case success(Output)
        case failure(Error)
    }
}

#76 Equatable & Hashable structures

🤖 Now that the Swift compiler automatically synthesizes Equatable & Hashable conformances for value types, it's easier than ever to setup model structures with nested types that are all Equatable/Hashable!

typealias Value = Hashable & Codable

struct User: Value {
    var name: String
    var age: Int
    var lastLoginDate: Date?
    var settings: Settings
}

extension User {
    struct Settings: Value {
        var itemsPerPage: Int
        var theme: Theme
    }
}

extension User.Settings {
    enum Theme: String, Value {
        case light
        case dark
    }
}

You can read more about using nested types in Swift here.

#75 Conditional conformances

🎉 Swift 4.1 is here! One of the key features it brings is conditional conformances, which lets you have a type only conform to a protocol under certain constraints.

protocol UnboxTransformable {
    associatedtype RawValue

    static func transform(_ value: RawValue) throws -> Self?
}

extension Array: UnboxTransformable where Element: UnboxTransformable {
    typealias RawValue = [Element.RawValue]

    static func transform(_ value: RawValue) throws -> [Element]? {
        return try value.compactMap(Element.transform)
    }
}

I also have an article with lots of more info on conditional conformances here. Paul Hudson also has a great overview of all Swift 4.1 features here.

#74 Generic type aliases

🕵️‍♀️ A cool thing about Swift type aliases is that they can be generic! Combine that with tuples and you can easily define simple generic types.

typealias Pair<T> = (T, T)

extension Game {
    func calculateScore(for players: Pair<Player>) -> Int {
        ...
    }
}

You can read more about using tuples as lightweight types here.

#73 Parsing command line arguments using UserDefaults

☑️ A really cool "hidden" feature of UserDefaults is that it contains any arguments that were passed to the app at launch!

Super useful both in Swift command line tools & scripts, but also to temporarily override a value when debugging iOS apps.

let defaults = UserDefaults.standard
let query = defaults.string(forKey: "query")
let resultCount = defaults.integer(forKey: "results")

#72 Using the & operator

👏 Swift's & operator is awesome! Not only can you use it to compose protocols, you can compose other types too! Very useful if you want to hide concrete types & implementation details.

protocol LoadableFromURL {
    func load(from url: URL)
}

class ContentViewController: UIViewController, LoadableFromURL {
    func load(from url: URL) {
        ...
    }
}

class ViewControllerFactory {
    func makeContentViewController() -> UIViewController & LoadableFromURL {
        return ContentViewController()
    }
}

#71 Capturing multiple values in mocks

🤗 When capturing values in mocks, using an array (instead of just a single value) makes it easy to verify that only a certain number of values were passed.

Perfect for protecting against "over-calling" something.

class UserManagerTests: XCTestCase {
    func testObserversCalledWhenUserFirstLogsIn() {
        let manager = UserManager()

        let observer = ObserverMock()
        manager.addObserver(observer)

        // First login, observers should be notified
        let user = User(id: 123, name: "John")
        manager.userDidLogin(user)
        XCTAssertEqual(observer.users, [user])

        // If the same user logs in again, observers shouldn't be notified
        manager.userDidLogin(user)
        XCTAssertEqual(observer.users, [user])
    }
}

private extension UserManagerTests {
    class ObserverMock: UserManagerObserver {
        private(set) var users = [User]()

        func userDidChange(to user: User) {
            users.append(user)
        }
    }
}

#70 Reducing the need for mocks

👋 When writing tests, you don't always need to create mocks - you can create stubs using real instances of things like errors, URLs & UserDefaults.

Here's how to do that for some common tasks/object types in Swift:

// Create errors using NSError (#function can be used to reference the name of the test)
let error = NSError(domain: #function, code: 1, userInfo: nil)

// Create non-optional URLs using file paths
let url = URL(fileURLWithPath: "Some/URL")

// Reference the test bundle using Bundle(for:)
let bundle = Bundle(for: type(of: self))

// Create an explicit UserDefaults object (instead of having to use a mock)
let userDefaults = UserDefaults(suiteName: #function)

// Create queues to control/await concurrent operations
let queue = DispatchQueue(label: #function)

For when you actually do need mocking, check out "Mocking in Swift".

#69 Using "then" as an external parameter label for closures

⏱ I've started using "then" as an external parameter label for completion handlers. Makes the call site read really nicely (Because I do ❤️ conversational API design) regardless of whether trailing closure syntax is used or not.

protocol DataLoader {
    // Adding type aliases to protocols can be a great way to
    // reduce verbosity for parameter types.
    typealias Handler = (Result<Data>) -> Void
    associatedtype Endpoint

    func loadData(from endpoint: Endpoint, then handler: @escaping Handler)
}

loader.loadData(from: .messages) { result in
    ...
}

loader.loadData(from: .messages, then: { result in
    ...
})

#68 Combining lazily evaluated sequences with the builder pattern

😴 Combining lazily evaluated sequences with builder pattern-like properties can lead to some pretty sweet APIs for configurable sequences in Swift.

Also useful for queries & other things you "build up" and then execute.

// Extension adding builder pattern-like properties that return
// a new sequence value with the given configuration applied
extension FileSequence {
    var recursive: FileSequence {
        var sequence = self
        sequence.isRecursive = true
        return sequence
    }

    var includingHidden: FileSequence {
        var sequence = self
        sequence.includeHidden = true
        return sequence
    }
}

// BEFORE

let files = folder.makeFileSequence(recursive: true, includeHidden: true)

// AFTER

let files = folder.files.recursive.includingHidden

Want an intro to lazy sequences? Check out "Swift sequences: The art of being lazy".

#67 Faster & more stable UI tests

My top 3 tips for faster & more stable UI tests:

📱 Reset the app's state at the beginning of every test.

🆔 Use accessibility identifiers instead of UI strings.

⏱ Use expectations instead of waiting time.

func testOpeningArticle() {
    // Launch the app with an argument that tells it to reset its state
    let app = XCUIApplication()
    app.launchArguments.append("--uitesting")
    app.launch()
    
    // Check that the app is displaying an activity indicator
    let activityIndicator = app.activityIndicator.element
    XCTAssertTrue(activityIndicator.exists)
    
    // Wait for the loading indicator to disappear = content is ready
    expectation(for: NSPredicate(format: "exists == 0"),
                evaluatedWith: activityIndicator)
                
    // Use a generous timeout in case the network is slow
    waitForExpectations(timeout: 10)
    
    // Tap the cell for the first article
    app.tables.cells["Article.0"].tap()
    
    // Assert that a label with the accessibility identifier "Article.Title" exists
    let label = app.staticTexts["Article.Title"]
    XCTAssertTrue(label.exists)
}

#66 Accessing the clipboard from a Swift script

📋 It's super easy to access the contents of the clipboard from a Swift script. A big benefit of Swift scripting is being able to use Cocoa's powerful APIs for Mac apps.

import Cocoa

let clipboard = NSPasteboard.general.string(forType: .string)

#65 Using tuples for view state

🎯 Using Swift tuples for view state can be a super nice way to group multiple properties together and render them reactively using the layout system.

By using a tuple we don't have to either introduce a new type or make our view model-aware.

class TextView: UIView {
    var state: (title: String?, text: String?) {
        // By telling UIKit that our view needs layout and binding our
        // state in layoutSubviews, we can react to state changes without
        // doing unnecessary layout work.
        didSet { setNeedsLayout() }
    }

    private let titleLabel = UILabel()
    private let textLabel = UILabel()

    override func layoutSubviews() {
        super.layoutSubviews()

        titleLabel.text = state.title
        textLabel.text = state.text

        ...
    }
}

#64 Throwing tests and LocalizedError

⚾️ Swift tests can throw, which is super useful in order to avoid complicated logic or force unwrapping. By making errors conform to LocalizedError, you can also get a nice error message in Xcode if there's a failure.

class ImageCacheTests: XCTestCase {
    func testCachingAndLoadingImage() throws {
        let bundle = Bundle(for: type(of: self))
        let cache = ImageCache(bundle: bundle)
        
        // Bonus tip: You can easily load images from your test
        // bundle using this UIImage initializer
        let image = try require(UIImage(named: "sample", in: bundle, compatibleWith: nil))
        try cache.cache(image, forKey: "key")
        
        let cachedImage = try cache.image(forKey: "key")
        XCTAssertEqual(image, cachedImage)
    }
}

enum ImageCacheError {
    case emptyKey
    case dataConversionFailed
}

// When using throwing tests, making your errors conform to
// LocalizedError will render a much nicer error message in
// Xcode (per default only the error code is shown).
extension ImageCacheError: LocalizedError {
    var errorDescription: String? {
        switch self {
        case .emptyKey:
            return "An empty key was given"
        case .dataConversionFailed:
            return "Failed to convert the given image to Data"
        }
    }
}

For more information, and the implementation of the require method used above, check out "Avoiding force unwrapping in Swift unit tests".

#63 The difference between static and class properties

✍️ Unlike static properties, class properties can be overridden by subclasses (however, they can't be stored, only computed).

class TableViewCell: UITableViewCell {
    class var preferredHeight: CGFloat { return 60 }
}

class TallTableViewCell: TableViewCell {
    override class var preferredHeight: CGFloat { return 100 }
}

#62 Creating extensions with static factory methods

👨‍🎨 Creating extensions with static factory methods can be a great alternative to subclassing in Swift, especially for things like setting up UIViews, CALayers or other kinds of styling.

It also lets you remove a lot of styling & setup from your view controllers.

extension UILabel {
    static func makeForTitle() -> UILabel {
        let label = UILabel()
        label.font = .boldSystemFont(ofSize: 24)
        label.textColor = .darkGray
        label.adjustsFontSizeToFitWidth = true
        label.minimumScaleFactor = 0.75
        return label
    }

    static func makeForText() -> UILabel {
        let label = UILabel()
        label.font = .systemFont(ofSize: 16)
        label.textColor = .black
        label.numberOfLines = 0
        return label
    }
}

class ArticleViewController: UIViewController {
    lazy var titleLabel = UILabel.makeForTitle()
    lazy var textLabel = UILabel.makeForText()
}

#61 Child view controller auto-resizing

🧒 An awesome thing about child view controllers is that they're automatically resized to match their parent, making them a super nice solution for things like loading & error views.

class ListViewController: UIViewController {
    func loadItems() {
        let loadingViewController = LoadingViewController()
        add(loadingViewController)

        dataLoader.loadItems { [weak self] result in
            loadingViewController.remove()
            self?.handle(result)
        }
    }
}

For more about child view controller (including the add and remove methods used above), check out "Using child view controllers as plugins in Swift".

#60 Using zip

🤐 Using the zip function in Swift you can easily combine two sequences. Super useful when using two sequences to do some work, since zip takes care of all the bounds-checking.

func render(titles: [String]) {
    for (label, text) in zip(titleLabels, titles) {
        print(text)
        label.text = text
    }
}

#59 Defining custom option sets

🎛 The awesome thing about option sets in Swift is that they can automatically either be passed as a single member or as a set. Even cooler is that you can easily define your own option sets as well, perfect for options and other non-exclusive values.

// Option sets are awesome, because you can easily pass them
// both using dot syntax and array literal syntax, like when
// using the UIView animation API:
UIView.animate(withDuration: 0.3,
               delay: 0,
               options: .allowUserInteraction,
               animations: animations)

UIView.animate(withDuration: 0.3,
               delay: 0,
               options: [.allowUserInteraction, .layoutSubviews],
               animations: animations)

// The cool thing is that you can easily define your own option
// sets as well, by defining a struct that has an Int rawValue,
// that will be used as a bit mask.
extension Cache {
    struct Options: OptionSet {
        static let saveToDisk = Options(rawValue: 1)
        static let clearOnMemoryWarning = Options(rawValue: 1 << 1)
        static let clearDaily = Options(rawValue: 1 << 2)

        let rawValue: Int
    }
}

// We can now use Cache.Options just like UIViewAnimationOptions:
Cache(options: .saveToDisk)
Cache(options: [.saveToDisk, .clearDaily])

#58 Using the where clause with associated types

🙌 Using the where clause when designing protocol-oriented APIs in Swift can let your implementations (or others' if it's open source) have a lot more freedom, especially when it comes to collections.

See "Using generic type constraints in Swift 4" for more info.

public protocol PathFinderMap {
    associatedtype Node
    // Using the 'where' clause for associated types, we can
    // ensure that a type meets certain requirements (in this
    // case that it's a sequence with Node elements).
    associatedtype NodeSequence: Sequence where NodeSequence.Element == Node

    // Instead of using a concrete type (like [Node]) here, we
    // give implementors of this protocol more freedom while
    // still meeting our requirements. For example, one
    // implementation might use Set<Node>.
    func neighbors(of node: Node) -> NodeSequence
}

#57 Using first class functions when iterating over a dictionary

👨‍🍳 Combine first class functions in Swift with the fact that Dictionary elements are (Key, Value) tuples and you can build yourself some pretty awesome functional chains when iterating over a Dictionary.

func makeActor(at coordinate: Coordinate, for building: Building) -> Actor {
    let actor = Actor()
    actor.position = coordinate.point
    actor.animation = building.animation
    return actor
}

func render(_ buildings: [Coordinate : Building]) {
    buildings.map(makeActor).forEach(add)
}

#56 Calling instance methods as static functions

😎 In Swift, you can call any instance method as a static function and it will return a closure representing that method. This is how running tests using SPM on Linux works.

More about this topic in my blog post "First class functions in Swift".

// This produces a '() -> Void' closure which is a reference to the
// given view's 'removeFromSuperview' method.
let closure = UIView.removeFromSuperview(view)

// We can now call it just like we would any other closure, and it
// will run 'view.removeFromSuperview()'
closure()

// This is how running tests using the Swift Package Manager on Linux
// works, you return your test functions as closures:
extension UserManagerTests {
    static var allTests = [
        ("testLoggingIn", testLoggingIn),
        ("testLoggingOut", testLoggingOut),
        ("testUserPermissions", testUserPermissions)
    ]
}

#55 Dropping suffixes from method names to support multiple arguments

👏 One really nice benefit of dropping suffixes from method names (and just using verbs, when possible) is that it becomes super easy to support both single and multiple arguments, and it works really well semantically.

extension UIView {
    func add(_ subviews: UIView...) {
        subviews.forEach(addSubview)
    }
}

view.add(button)
view.add(label)

// By dropping the "Subview" suffix from the method name, both
// single and multiple arguments work really well semantically.
view.add(button, label)

#54 Constraining protocols to classes to ensure mutability

👽 Using the AnyObject (or class) constraint on protocols is not only useful when defining delegates (or other weak references), but also when you always want instances to be mutable without copying.

// By constraining a protocol with 'AnyObject' it can only be adopted
// by classes, which means all instances will always be mutable, and
// that it's the original instance (not a copy) that will be mutated.
protocol DataContainer: AnyObject {
    var data: Data? { get set }
}

class UserSettingsManager {
    private var settings: Settings
    private let dataContainer: DataContainer

    // Since DataContainer is a protocol, we an easily mock it in
    // tests if we use dependency injection
    init(settings: Settings, dataContainer: DataContainer) {
        self.settings = settings
        self.dataContainer = dataContainer
    }

    func saveSettings() throws {
        let data = try settings.serialize()

        // We can now assign properties on an instance of our protocol
        // because the compiler knows it's always going to be a class
        dataContainer.data = data
    }
}

#53 String-based enums in string interpolation

🍣 Even if you define a custom raw value for a string-based enum in Swift, the full case name will be used in string interpolation.

Super useful when using separate raw values for JSON, while still wanting to use the full case name in other contexts.

extension Building {
    // This enum has custom raw values that are used when decoding
    // a value, for example from JSON.
    enum Kind: String {
        case castle = "C"
        case town = "T"
        case barracks = "B"
        case goldMine = "G"
        case camp = "CA"
        case blacksmith = "BL"
    }

    var animation: Animation {
        return Animation(
            // When used in string interpolation, the full case name is still used.
            // For 'castle' this will be 'buildings/castle'.
            name: "buildings/\(kind)",
            frameCount: frameCount,
            frameDuration: frameDuration
        )
    }
}

#52 Expressively comparing a value with a list of candidates

👨‍🔬 Continuing to experiment with expressive ways of comparing a value with a list of candidates in Swift. Adding an extension on Equatable is probably my favorite approach so far.

extension Equatable {
    func isAny(of candidates: Self...) -> Bool {
        return candidates.contains(self)
    }
}

let isHorizontal = direction.isAny(of: .left, .right)

See tip #35 for my previous experiment.

#51 UIView bounds and transforms

📐 A really interesting side-effect of a UIView's bounds being its rect within its own coordinate system is that transforms don't affect it at all. That's why it's usually a better fit than frame when doing layout calculations of subviews.

let view = UIView()
view.frame.size = CGSize(width: 100, height: 100)
view.transform = CGAffineTransform(scaleX: 2, y: 2)

print(view.frame) // (-50.0, -50.0, 200.0, 200.0)
print(view.bounds) // (0.0, 0.0, 100.0, 100.0)

#50 UIKit default arguments

👏 It's awesome that many UIKit APIs with completion handlers and other optional parameters import into Swift with default arguments (even though they are written in Objective-C). Getting rid of all those nil arguments is so nice!

// BEFORE: All parameters are specified, just like in Objective-C

viewController.present(modalViewController, animated: true, completion: nil)

modalViewController.dismiss(animated: true, completion: nil)

viewController.transition(from: loadingViewController,
                          to: contentViewController,
                          duration: 0.3,
                          options: [],
                          animations: animations,
                          completion: nil)

// AFTER: Since many UIKit APIs with completion handlers and other
// optional parameters import into Swift with default arguments,
// we can make our calls shorter

viewController.present(modalViewController, animated: true)

modalViewController.dismiss(animated: true)

viewController.transition(from: loadingViewController,
                          to: contentViewController,
                          duration: 0.3,
                          animations: animations)

#49 Avoiding Massive View Controllers

✂️ Avoiding Massive View Controllers is all about finding the right levels of abstraction and splitting things up.

My personal rule of thumb is that as soon as I have 3 methods or properties that have the same prefix, I break them out into their own type.

// BEFORE

class LoginViewController: UIViewController {
    private lazy var signUpLabel = UILabel()
    private lazy var signUpImageView = UIImageView()
    private lazy var signUpButton = UIButton()
}

// AFTER

class LoginViewController: UIViewController {
    private lazy var signUpView = SignUpView()
}

class SignUpView: UIView {
    private lazy var label = UILabel()
    private lazy var imageView = UIImageView()
    private lazy var button = UIButton()
}

#48 Extending optionals

❤️ I love the fact that optionals are enums in Swift - it makes it so easy to extend them with convenience APIs for certain types. Especially useful when doing things like data validation on optional values.

func validateTextFields() -> Bool {
    guard !usernameTextField.text.isNilOrEmpty else {
        return false
    }

    ...

    return true
}

// Since all optionals are actual enum values in Swift, we can easily
// extend them for certain types, to add our own convenience APIs

extension Optional where Wrapped == String {
    var isNilOrEmpty: Bool {
        switch self {
        case let string?:
            return string.isEmpty
        case nil:
            return true
        }
    }
}

// Since strings are now Collections in Swift 4, you can even
// add this property to all optional collections:

extension Optional where Wrapped: Collection {
    var isNilOrEmpty: Bool {
        switch self {
        case let collection?:
            return collection.isEmpty
        case nil:
            return true
        }
    }
}

#47 Using where with for-loops

🗺 Using the where keyword can be a super nice way to quickly apply a filter in a for-loop in Swift. You can of course use map, filter and forEach, or guard, but for simple loops I think this is very expressive and nice.

func archiveMarkedPosts() {
    for post in posts where post.isMarked {
        archive(post)
    }
}

func healAllies() {
    for player in players where player.isAllied(to: currentPlayer) {
        player.heal()
    }
}

#46 Variable shadowing

👻 Variable shadowing can be super useful in Swift, especially when you want to create a local copy of a parameter value in order to use it as state within a closure.

init(repeatMode: RepeatMode, closure: @escaping () -> UpdateOutcome) {
    // Shadow the argument with a local, mutable copy
    var repeatMode = repeatMode
    
    self.closure = {
        // With shadowing, there's no risk of accidentially
        // referring to the immutable version
        switch repeatMode {
        case .forever:
            break
        case .times(let count):
            guard count > 0 else {
                return .finished
            }
            
            // We can now capture the mutable version and use
            // it for state in a closure
            repeatMode = .times(count - 1)
        }
        
        return closure()
    }
}

#45 Using dot syntax for static properties and initializers

✒️ Dot syntax is one of my favorite features of Swift. What's really cool is that it's not only for enums, any static method or property can be used with dot syntax - even initializers! Perfect for convenience APIs and default parameters.

public enum RepeatMode {
    case times(Int)
    case forever
}

public extension RepeatMode {
    static var never: RepeatMode {
        return .times(0)
    }

    static var once: RepeatMode {
        return .times(1)
    }
}

view.perform(animation, repeated: .once)

// To make default parameters more compact, you can even use init with dot syntax

class ImageLoader {
    init(cache: Cache = .init(), decoder: ImageDecoder = .init()) {
        ...
    }
}

#44 Calling functions as closures with a tuple as parameters

🚀 One really cool aspect of Swift having first class functions is that you can pass any function (or even initializer) as a closure, and even call it with a tuple containing its parameters!

// This function lets us treat any "normal" function or method as
// a closure and run it with a tuple that contains its parameters
func call<Input, Output>(_ function: (Input) -> Output, with input: Input) -> Output {
    return function(input)
}

class ViewFactory {
    func makeHeaderView() -> HeaderView {
        // We can now pass an initializer as a closure, and a tuple
        // containing its parameters
        return call(HeaderView.init, with: loadTextStyles())
    }
    
    private func loadTextStyles() -> (font: UIFont, color: UIColor) {
        return (theme.font, theme.textColor)
    }
}

class HeaderView {
    init(font: UIFont, textColor: UIColor) {
        ...
    }
}

#43 Enabling static dependency injection

💉 If you've been struggling to test code that uses static APIs, here's a technique you can use to enable static dependency injection without having to modify any call sites:

// Before: Almost impossible to test due to the use of singletons

class Analytics {
    static func log(_ event: Event) {
        Database.shared.save(event)
        
        let dictionary = event.serialize()
        NetworkManager.shared.post(dictionary, to: eventURL)
    }
}

// After: Much easier to test, since we can inject mocks as arguments

class Analytics {
    static func log(_ event: Event,
                    database: Database = .shared,
                    networkManager: NetworkManager = .shared) {
        database.save(event)
        
        let dictionary = event.serialize()
        networkManager.post(dictionary, to: eventURL)
    }
}

#42 Type inference for lazy properties in Swift 4

🎉 In Swift 4, type inference works for lazy properties and you don't need to explicitly refer to self!

// Swift 3

class PurchaseView: UIView {
    private lazy var buyButton: UIButton = self.makeBuyButton()
    
    private func makeBuyButton() -> UIButton {
        let button = UIButton()
        button.setTitle("Buy", for: .normal)
        button.setTitleColor(.blue, for: .normal)
        return button
    }
}

// Swift 4

class PurchaseView: UIView {
    private lazy var buyButton = makeBuyButton()
    
    private func makeBuyButton() -> UIButton {
        let button = UIButton()
        button.setTitle("Buy", for: .normal)
        button.setTitleColor(.blue, for: .normal)
        return button
    }
}

#41 Converting Swift errors to NSError

😎 You can turn any Swift Error into an NSError, which is super useful when pattern matching with a code 👍. Also, switching on optionals is pretty cool!

let task = urlSession.dataTask(with: url) { data, _, error in
    switch error {
    case .some(let error as NSError) where error.code == NSURLErrorNotConnectedToInternet:
        presenter.showOfflineView()
    case .some(let error):
        presenter.showGenericErrorView()
    case .none:
        presenter.renderContent(from: data)
    }
}

task.resume()

Also make sure to check out Kostas Kremizas' tip about how you can pattern match directly against a member of URLError.

#40 Making UIImage macOS compatible

🖥 Here's an easy way to make iOS model code that uses UIImage macOS compatible - like me and Gui Rambo discussed on the Swift by Sundell Podcast.

// Either put this in a separate file that you only include in your macOS target or wrap the code in #if os(macOS) / #endif

import Cocoa

// Step 1: Typealias UIImage to NSImage
typealias UIImage = NSImage

// Step 2: You might want to add these APIs that UIImage has but NSImage doesn't.
extension NSImage {
    var cgImage: CGImage? {
        var proposedRect = CGRect(origin: .zero, size: size)

        return cgImage(forProposedRect: &proposedRect,
                       context: nil,
                       hints: nil)
    }

    convenience init?(named name: String) {
        self.init(named: Name(name))
    }
}

// Step 3: Profit - you can now make your model code that uses UIImage cross-platform!
struct User {
    let name: String
    let profileImage: UIImage
}

#39 Internally mutable protocol-oriented APIs

🤖 You can easily define a protocol-oriented API that can only be mutated internally, by using an internal protocol that extends a public one.

// Declare a public protocol that acts as your immutable API
public protocol ModelHolder {
    associatedtype Model
    var model: Model { get }
}

// Declare an extended, internal protocol that provides a mutable API
internal protocol MutableModelHolder: ModelHolder {
    var model: Model { get set }
}

// You can now implement the requirements using 'public internal(set)'
public class UserHolder: MutableModelHolder {
    public internal(set) var model: User

    internal init(model: User) {
        self.model = model
    }
}

#38 Switching on a set

🎛 You can switch on a set using array literals as cases in Swift! Can be really useful to avoid many if/else if statements.

class RoadTile: Tile {
    var connectedDirections = Set<Direction>()

    func render() {
        switch connectedDirections {
        case [.up, .down]:
            image = UIImage(named: "road-vertical")
        case [.left, .right]:
            image = UIImage(named: "road-horizontal")
        default:
            image = UIImage(named: "road")
        }
    }
}

#37 Adding the current locale to cache keys

🌍 When caching localized content in an app, it's a good idea to add the current locale to all keys, to prevent bugs when switching languages.

func cache(_ content: Content, forKey key: String) throws {
    let data = try wrap(content) as Data
    let key = localize(key: key)
    try storage.store(data, forKey: key)
}

func loadCachedContent(forKey key: String) -> Content? {
    let key = localize(key: key)
    let data = storage.loadData(forKey: key)
    return data.flatMap { try? unbox(data: $0) }
}

private func localize(key: String) -> String {
    return key + "-" + Bundle.main.preferredLocalizations[0]
}

#36 Setting up tests to avoid retain cycles with weak references

🚳 Here's an easy way to setup a test to avoid accidental retain cycles with object relationships (like weak delegates & observers) in Swift:

func testDelegateNotRetained() {
    // Assign the delegate (weak) and also retain it using a local var
    var delegate: Delegate? = DelegateMock()
    controller.delegate = delegate
    XCTAssertNotNil(controller.delegate)
    
    // Release the local var, which should also release the weak reference
    delegate = nil
    XCTAssertNil(controller.delegate)
}

#35 Expressively matching a value against a list of candidates

👨‍🔬 Playing around with an expressive way to check if a value matches any of a list of candidates in Swift:

// Instead of multiple conditions like this:

if string == "One" || string == "Two" || string == "Three" {

}

// You can now do:

if string == any(of: "One", "Two", "Three") {

}

You can find a gist with the implementation here.

#34 Organizing code using extensions

👪 APIs in a Swift extension automatically inherit its access control level, making it a neat way to organize public, internal & private APIs.

public extension Animation {
    init(textureNamed textureName: String) {
        frames = [Texture(name: textureName)]
    }
    
    init(texturesNamed textureNames: [String], frameDuration: TimeInterval = 1) {
        frames = textureNames.map(Texture.init)
        self.frameDuration = frameDuration
    }
    
    init(image: Image) {
        frames = [Texture(image: image)]
    }
}

internal extension Animation {
    func loadFrameImages() -> [Image] {
        return frames.map { $0.loadImageIfNeeded() }
    }
}

#33 Using map to transform an optional into a Result type

🗺 Using map you can transform an optional value into an optional Result type by simply passing in the enum case.

enum Result<Value> {
    case value(Value)
    case error(Error)
}

class Promise<Value> {
    private var result: Result<Value>?
    
    init(value: Value? = nil) {
        result = value.map(Result.value)
    }
}

#32 Assigning to self in struct initializers

👌 It's so nice that you can assign directly to self in struct initializers in Swift. Very useful when adding conformance to protocols.

extension Bool: AnswerConvertible {
    public init(input: String) throws {
        switch input.lowercased() {
        case "y", "yes", "👍":
            self = true
        default:
            self = false
        }
    }
}

#31 Recursively calling closures as inline functions

☎️ Defining Swift closures as inline functions enables you to recursively call them, which is super useful in things like custom sequences.

class Database {
    func records(matching query: Query) -> AnySequence<Record> {
        var recordIterator = loadRecords().makeIterator()
        
        func iterate() -> Record? {
            guard let nextRecord = recordIterator.next() else {
                return nil
            }
            
            guard nextRecord.matches(query) else {
                // Since the closure is an inline function, it can be recursively called,
                // in this case in order to advance to the next item.
                return iterate()
            }
            
            return nextRecord
        }
        
        // AnySequence/AnyIterator are part of the standard library and provide an easy way
        // to define custom sequences using closures.
        return AnySequence { AnyIterator(iterate) }
    }
}

Rob Napier points out that using the above might cause crashes if used on a large databaset, since Swift has no guaranteed Tail Call Optimization (TCO).

Slava Pestov also points out that another benefit of inline functions vs closures is that they can have their own generic parameter list.

#30 Passing self to required Objective-C dependencies

🏖 Using lazy properties in Swift, you can pass self to required Objective-C dependencies without having to use force-unwrapped optionals.

class DataLoader: NSObject {
    lazy var urlSession: URLSession = self.makeURLSession()
    
    private func makeURLSession() -> URLSession {
        return URLSession(configuration: .default, delegate: self, delegateQueue: .main)
    }
}

class Renderer {
    lazy var displayLink: CADisplayLink = self.makeDisplayLink()
    
    private func makeDisplayLink() -> CADisplayLink {
        return CADisplayLink(target: self, selector: #selector(screenDidRefresh))
    }
}

#29 Making weak or lazy properties readonly

👓 If you have a property in Swift that needs to be weak or lazy, you can still make it readonly by using private(set).

class Node {
    private(set) weak var parent: Node?
    private(set) lazy var children = [Node]()

    func add(child: Node) {
        children.append(child)
        child.parent = self
    }
}

#28 Defining static URLs using string literals

🌏 Tired of using URL(string: "url")! for static URLs? Make URL conform to ExpressibleByStringLiteral and you can now simply use "url" instead.

extension URL: ExpressibleByStringLiteral {
    // By using 'StaticString' we disable string interpolation, for safety
    public init(stringLiteral value: StaticString) {
        self = URL(string: "\(value)").require(hint: "Invalid URL string literal: \(value)")
    }
}

// We can now define URLs using static string literals 🎉
let url: URL = "https://www.swiftbysundell.com"
let task = URLSession.shared.dataTask(with: "https://www.swiftbysundell.com")

// In Swift 3 or earlier, you also have to implement 2 additional initializers
extension URL {
    public init(extendedGraphemeClusterLiteral value: StaticString) {
        self.init(stringLiteral: value)
    }

    public init(unicodeScalarLiteral value: StaticString) {
        self.init(stringLiteral: value)
    }
}

To find the extension that adds the require() method on Optional that I use above, check out Require.

#27 Manipulating points, sizes and frames using math operators

✚ I'm always careful with operator overloading, but for manipulating things like sizes, points & frames I find them super useful.

extension CGSize {
    static func *(lhs: CGSize, rhs: CGFloat) -> CGSize {
        return CGSize(width: lhs.width * rhs, height: lhs.height * rhs)
    }
}

button.frame.size = image.size * 2

If you like the above idea, check out CGOperators, which contains math operator overloads for all Core Graphics' vector types.

#26 Using closure types in generic constraints

🔗 You can use closure types in generic constraints in Swift. Enables nice APIs for handling sequences of closures.

extension Sequence where Element == () -> Void {
    func callAll() {
        forEach { $0() }
    }
}

extension Sequence where Element == () -> String {
    func joinedResults(separator: String) -> String {
        return map { $0() }.joined(separator: separator)
    }
}

callbacks.callAll()
let names = nameProviders.joinedResults(separator: ", ")

(If you're using Swift 3, you have to change Element to Iterator.Element)

#25 Using associated enum values to avoid state-specific optionals

🎉 Using associated enum values is a super nice way to encapsulate mutually exclusive state info (and avoiding state-specific optionals).

// BEFORE: Lots of state-specific, optional properties

class Player {
    var isWaitingForMatchMaking: Bool
    var invitingUser: User?
    var numberOfLives: Int
    var playerDefeatedBy: Player?
    var roundDefeatedIn: Int?
}

// AFTER: All state-specific information is encapsulated in enum cases

class Player {
    enum State {
        case waitingForMatchMaking
        case waitingForInviteResponse(from: User)
        case active(numberOfLives: Int)
        case defeated(by: Player, roundNumber: Int)
    }
    
    var state: State
}

#24 Using enums for async result types

👍 I really like using enums for all async result types, even boolean ones. Self-documenting, and makes the call site a lot nicer to read too!

protocol PushNotificationService {
    // Before
    func enablePushNotifications(completionHandler: @escaping (Bool) -> Void)
    
    // After
    func enablePushNotifications(completionHandler: @escaping (PushNotificationStatus) -> Void)
}

enum PushNotificationStatus {
    case enabled
    case disabled
}

service.enablePushNotifications { status in
    if status == .enabled {
        enableNotificationsButton.removeFromSuperview()
    }
}

#23 Working on async code in a playground

🏃 Want to work on your async code in a Swift Playground? Just set needsIndefiniteExecution to true to keep it running:

import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

DispatchQueue.main.asyncAfter(deadline: .now() + 3) {
    let greeting = "Hello after 3 seconds"
    print(greeting)
}

To stop the playground from executing, simply call PlaygroundPage.current.finishExecution().

#22 Overriding self with a weak reference

💦 Avoid memory leaks when accidentially refering to self in closures by overriding it locally with a weak reference:

Swift >= 4.2

dataLoader.loadData(from: url) { [weak self] result in
    guard let self = self else { 
        return 
    }

    self.cache(result)
    
    ...

Swift < 4.2

dataLoader.loadData(from: url) { [weak self] result in
    guard let `self` = self else {
        return
    }

    self.cache(result)
    
    ...

Note that the reason the above currently works is because of a compiler bug (which I hope gets turned into a properly supported feature soon).

#21 Using DispatchWorkItem

🕓 Using dispatch work items you can easily cancel a delayed asynchronous GCD task if you no longer need it:

let workItem = DispatchWorkItem {
    // Your async code goes in here
}

// Execute the work item after 1 second
DispatchQueue.main.asyncAfter(deadline: .now() + 1, execute: workItem)

// You can cancel the work item if you no longer need it
workItem.cancel()

#20 Combining a sequence of functions

➕ While working on a new Swift developer tool (to be open sourced soon 😉), I came up with a pretty neat way of organizing its sequence of operations, by combining their functions into a closure:

internal func +<A, B, C>(lhs: @escaping (A) throws -> B,
                         rhs: @escaping (B) throws -> C) -> (A) throws -> C {
    return { try rhs(lhs($0)) }
}

public func run() throws {
    try (determineTarget + build + analyze + output)()
}

If you're familiar with the functional programming world, you might know the above technique as the pipe operator (thanks to Alexey Demedreckiy for pointing this out!)

#19 Chaining optionals with map() and flatMap()

🗺 Using map() and flatMap() on optionals you can chain multiple operations without having to use lengthy if lets or guards:

// BEFORE

guard let string = argument(at: 1) else {
    return
}

guard let url = URL(string: string) else {
    return
}

handle(url)

// AFTER

argument(at: 1).flatMap(URL.init).map(handle)

#18 Using self-executing closures for lazy properties

🚀 Using self-executing closures is a great way to encapsulate lazy property initialization:

class StoreViewController: UIViewController {
    private lazy var collectionView: UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        let view = UICollectionView(frame: self.view.bounds, collectionViewLayout: layout)
        view.delegate = self
        view.dataSource = self
        return view
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(collectionView)
    }
}

#17 Speeding up Swift package tests

⚡️ You can speed up your Swift package tests using the --parallel flag. For Marathon, the tests execute 3 times faster that way!

swift test --parallel

#16 Avoiding mocking UserDefaults

🛠 Struggling with mocking UserDefaults in a test? The good news is: you don't need mocking - just create a real instance:

class LoginTests: XCTestCase {
    private var userDefaults: UserDefaults!
    private var manager: LoginManager!
    
    override func setUp() {
        super.setup()
        
        userDefaults = UserDefaults(suiteName: #file)
        userDefaults.removePersistentDomain(forName: #file)
        
        manager = LoginManager(userDefaults: userDefaults)
    }
}

#15 Using variadic parameters

👍 Using variadic parameters in Swift, you can create some really nice APIs that take a list of objects without having to use an array:

extension Canvas {
    func add(_ shapes: Shape...) {
        shapes.forEach(add)
    }
}

let circle = Circle(center: CGPoint(x: 5, y: 5), radius: 5)
let lineA = Line(start: .zero, end: CGPoint(x: 10, y: 10))
let lineB = Line(start: CGPoint(x: 0, y: 10), end: CGPoint(x: 10, y: 0))

let canvas = Canvas()
canvas.add(circle, lineA, lineB)
canvas.render()

#14 Referring to enum cases with associated values as closures

😮 Just like you can refer to a Swift function as a closure, you can do the same thing with enum cases with associated values:

enum UnboxPath {
    case key(String)
    case keyPath(String)
}

struct UserSchema {
    static let name = key("name")
    static let age = key("age")
    static let posts = key("posts")
    
    private static let key = UnboxPath.key
}

#13 Using the === operator to compare objects by instance

📈 The === operator lets you check if two objects are the same instance. Very useful when verifying that an array contains an instance in a test:

protocol InstanceEquatable: class, Equatable {}

extension InstanceEquatable {
    static func ==(lhs: Self, rhs: Self) -> Bool {
        return lhs === rhs
    }
}

extension Enemy: InstanceEquatable {}

func testDestroyingEnemy() {
    player.attack(enemy)
    XCTAssertTrue(player.destroyedEnemies.contains(enemy))
}

#12 Calling initializers with dot syntax and passing them as closures

😎 Cool thing about Swift initializers: you can call them using dot syntax and pass them as closures! Perfect for mocking dates in tests.

class Logger {
    private let storage: LogStorage
    private let dateProvider: () -> Date
    
    init(storage: LogStorage = .init(), dateProvider: @escaping () -> Date = Date.init) {
        self.storage = storage
        self.dateProvider = dateProvider
    }
    
    func log(event: Event) {
        storage.store(event: event, date: dateProvider())
    }
}

#11 Structuring UI tests as extensions on XCUIApplication

📱 Most of my UI testing logic is now categories on XCUIApplication. Makes the test cases really easy to read:

func testLoggingInAndOut() {
    XCTAssertFalse(app.userIsLoggedIn)
    
    app.launch()
    app.login()
    XCTAssertTrue(app.userIsLoggedIn)
    
    app.logout()
    XCTAssertFalse(app.userIsLoggedIn)
}

func testDisplayingCategories() {
    XCTAssertFalse(app.isDisplayingCategories)
    
    app.launch()
    app.login()
    app.goToCategories()
    XCTAssertTrue(app.isDisplayingCategories)
}

#10 Avoiding default cases in switch statements

🙂 It’s a good idea to avoid “default” cases when switching on Swift enums - it’ll “force you” to update your logic when a new case is added:

enum State {
    case loggedIn
    case loggedOut
    case onboarding
}

func handle(_ state: State) {
    switch state {
    case .loggedIn:
        showMainUI()
    case .loggedOut:
        showLoginUI()
    // Compiler error: Switch must be exhaustive
    }
}

#9 Using the guard statement in many different scopes

💂 It's really cool that you can use Swift's 'guard' statement to exit out of pretty much any scope, not only return from functions:

// You can use the 'guard' statement to...

for string in strings {
    // ...continue an iteration
    guard shouldProcess(string) else {
        continue
    }
    
    // ...or break it
    guard !shouldBreak(for: string) else {
        break
    }
    
    // ...or return
    guard !shouldReturn(for: string) else {
        return
    }
    
    // ..or throw an error
    guard string.isValid else {
        throw StringError.invalid(string)
    }
    
    // ...or exit the program
    guard !shouldExit(for: string) else {
        exit(1)
    }
}

#8 Passing functions & operators as closures

❤️ Love how you can pass functions & operators as closures in Swift. For example, it makes the syntax for sorting arrays really nice!

let array = [3, 9, 1, 4, 6, 2]
let sorted = array.sorted(by: <)

#7 Using #function for UserDefaults key consistency

🗝 Here's a neat little trick I use to get UserDefault key consistency in Swift (#function expands to the property name in getters/setters). Just remember to write a good suite of tests that'll guard you against bugs when changing property names.

extension UserDefaults {
    var onboardingCompleted: Bool {
        get { return bool(forKey: #function) }
        set { set(newValue, forKey: #function) }
    }
}

#6 Using a name already taken by the standard library

📛 Want to use a name already taken by the standard library for a nested type? No problem - just use Swift. to disambiguate:

extension Command {
    enum Error: Swift.Error {
        case missing
        case invalid(String)
    }
}

#5 Using Wrap to implement Equatable

📦 Playing around with using Wrap to implement Equatable for any type, primarily for testing:

protocol AutoEquatable: Equatable {}

extension AutoEquatable {
    static func ==(lhs: Self, rhs: Self) -> Bool {
        let lhsData = try! wrap(lhs) as Data
        let rhsData = try! wrap(rhs) as Data
        return lhsData == rhsData
    }
}

#4 Using typealiases to reduce the length of method signatures

📏 One thing that I find really useful in Swift is to use typealiases to reduce the length of method signatures in generic types:

public class PathFinder<Object: PathFinderObject> {
    public typealias Map = Object.Map
    public typealias Node = Map.Node
    public typealias Path = PathFinderPath<Object>
    
    public static func possiblePaths(for object: Object, at rootNode: Node, on map: Map) -> Path.Sequence {
        return .init(object: object, rootNode: rootNode, map: map)
    }
}

#3 Referencing either external or internal parameter name when writing docs

📖 You can reference either the external or internal parameter label when writing Swift docs - and they get parsed the same:

// EITHER:

class Foo {
    /**
    *   - parameter string: A string
    */
    func bar(with string: String) {}
}

// OR:

class Foo {
    /**
    *   - parameter with: A string
    */
    func bar(with string: String) {}
}

#2 Using auto closures

👍 Finding more and more uses for auto closures in Swift. Can enable some pretty nice APIs:

extension Dictionary {
    mutating func value(for key: Key, orAdd valueClosure: @autoclosure () -> Value) -> Value {
        if let value = self[key] {
            return value
        }
        
        let value = valueClosure()
        self[key] = value
        return value
    }
}

#1 Namespacing with nested types

🚀 I’ve started to become a really big fan of nested types in Swift. Love the additional namespacing it gives you!

public struct Map {
    public struct Model {
        public let size: Size
        public let theme: Theme
        public var terrain: [Position : Terrain.Model]
        public var units: [Position : Unit.Model]
        public var buildings: [Position : Building.Model]
    }
    
    public enum Direction {
        case up
        case right
        case down
        case left
    }
    
    public struct Position {
        public var x: Int
        public var y: Int
    }
    
    public enum Size: String {
        case small = "S"
        case medium = "M"
        case large = "L"
        case extraLarge = "XL"
    }
}

Download Details:

Author: JohnSundell
Source code: https://github.com/JohnSundell/SwiftTips

License: MIT license
#swift