MNO_lcp_dart: Unofficial Dart/Flutter Port Of The Readium 2 LCP Client

mno_lcp_dart

Flutter LCP implementation

This package provides a DART LCP layer. Important: the native libraries are not provided. Contact Edrlab to get the precompiled native libs, and contact@mantano.com to get the native wrapper lib

Use this package as a library

Depend on it

Run this command:

With Flutter:

 $ flutter pub add mno_lcp

This will add a line like this to your package's pubspec.yaml (and run an implicit flutter pub get):

dependencies:
  mno_lcp: ^0.1.0

Alternatively, your editor might support flutter pub get. Check the docs for your editor to learn more.

Import it

Now in your Dart code, you can use:

import 'package:mno_lcp/auth/lcp_passphrase_authentication.dart';
import 'package:mno_lcp/drm/drm_context.dart';
import 'package:mno_lcp/drm/drm_error.dart';
import 'package:mno_lcp/drm/drm_exception.dart';
import 'package:mno_lcp/drm/lcp_result.dart';
import 'package:mno_lcp/i18n/lcp_localizations.dart';
import 'package:mno_lcp/i18n/localizations/messages_all.dart';
import 'package:mno_lcp/i18n/localizations/messages_de.dart';
import 'package:mno_lcp/i18n/localizations/messages_en.dart';
import 'package:mno_lcp/i18n/localizations/messages_es.dart';
import 'package:mno_lcp/i18n/localizations/messages_fr.dart';
import 'package:mno_lcp/io/file_util.dart';
import 'package:mno_lcp/io/uint8list_converter.dart';
import 'package:mno_lcp/lcp.dart';
import 'package:mno_lcp/lcp_authenticating.dart';
import 'package:mno_lcp/lcp_client.dart';
import 'package:mno_lcp/lcp_content_protection.dart';
import 'package:mno_lcp/lcp_content_protection_service.dart';
import 'package:mno_lcp/lcp_decryptor.dart';
import 'package:mno_lcp/lcp_error.dart';
import 'package:mno_lcp/lcp_exception.dart';
import 'package:mno_lcp/lcp_license.dart';
import 'package:mno_lcp/lcp_parsing_error.dart';
import 'package:mno_lcp/lcp_service.dart';
import 'package:mno_lcp/license/container/bytes_license_container.dart';
import 'package:mno_lcp/license/container/epub_license_container.dart';
import 'package:mno_lcp/license/container/lcpl_license_container.dart';
import 'package:mno_lcp/license/container/license_container.dart';
import 'package:mno_lcp/license/container/web_pub_license_container.dart';
import 'package:mno_lcp/license/container/zip_license_container.dart';
import 'package:mno_lcp/license/license.dart';
import 'package:mno_lcp/license/license_validation.dart';
import 'package:mno_lcp/license/license_validation_events.dart';
import 'package:mno_lcp/license/license_validation_state_machine.dart';
import 'package:mno_lcp/license/license_validation_states.dart';
import 'package:mno_lcp/license/model/components/lcp/content_key.dart';
import 'package:mno_lcp/license/model/components/lcp/encryption.dart';
import 'package:mno_lcp/license/model/components/lcp/rights.dart';
import 'package:mno_lcp/license/model/components/lcp/signature.dart';
import 'package:mno_lcp/license/model/components/lcp/user.dart';
import 'package:mno_lcp/license/model/components/lcp/user_key.dart';
import 'package:mno_lcp/license/model/components/link.dart';
import 'package:mno_lcp/license/model/components/links.dart';
import 'package:mno_lcp/license/model/components/lsd/event.dart';
import 'package:mno_lcp/license/model/components/lsd/potential_rights.dart';
import 'package:mno_lcp/license/model/license_document.dart';
import 'package:mno_lcp/license/model/status_document.dart';
import 'package:mno_lcp/material_renew_listener.dart';
import 'package:mno_lcp/persistence/lcp_database.dart';
import 'package:mno_lcp/persistence/licenses.dart';
import 'package:mno_lcp/persistence/transactions.dart';
import 'package:mno_lcp/service/crl_service.dart';
import 'package:mno_lcp/service/device_repository.dart';
import 'package:mno_lcp/service/device_service.dart';
import 'package:mno_lcp/service/licenses_repository.dart';
import 'package:mno_lcp/service/licenses_service.dart';
import 'package:mno_lcp/service/network_service.dart';
import 'package:mno_lcp/service/passphrases_repository.dart';
import 'package:mno_lcp/service/passphrases_service.dart';
import 'package:mno_lcp/utils/zip_utils.dart';

example/lib/main.dart

// Copyright (c) 2021 Mantano. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:typed_data';

import 'package:mno_lcp/lcp.dart';
import 'package:mno_shared/src/publication/content_protection.dart';

Future<void> main() async {
  String passphrase = "passphrase";
  await Lcp.initLcp();
  LcpService? lcpService = await LcpServiceFactory.create(_LcpClientNative());
  if (lcpService != null) {
    ContentProtection contentProtection = lcpService.contentProtection(
        authentication: LcpPassphraseAuthentication(passphrase));
  }
}

class _LcpClientNative extends LcpClient {
  @override
  bool get isAvailable => true;

  @override
  DrmContext createContext(
      String jsonLicense, String hashedPassphrases, String pemCrl) {
    throw DRMException(DRMError.contextInvalid);
  }

  @override
  ByteData decrypt(DrmContext drmContext, ByteData encryptedData) =>
      ByteData(0);

  @override
  String findOneValidPassphrase(
      String jsonLicense, List<String> hashedPassphrases) {
    if (hashedPassphrases.isNotEmpty) {
      return hashedPassphrases.first;
    }
    throw DRMException(DRMError.licenseNoPasshphraseMatched);
  }
}

Download Details:

Author: Mantano
Source Code: https://github.com/Mantano/mno_lcp_dart 
License: BSD-3-Clause license

#flutter #dart 

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A Pure PHP Implementation Of The MessagePack Serialization Format

msgpack.php

A pure PHP implementation of the MessagePack serialization format.

Features

• Fully compliant with the latest MessagePack specification
• Supports streaming unpacking
• Supports unsigned 64-bit integers handling
• Supports object serialization
• Fully tested
• Relatively fast

Installation

The recommended way to install the library is through Composer:

composer require rybakit/msgpack

Usage

Packing

To pack values you can either use an instance of a Packer:

$packer = new Packer();
$packed = $packer->pack($value);

or call a static method on the MessagePack class:

$packed = MessagePack::pack($value);

In the examples above, the method pack automatically packs a value depending on its type. However, not all PHP types can be uniquely translated to MessagePack types. For example, the MessagePack format defines map and array types, which are represented by a single array type in PHP. By default, the packer will pack a PHP array as a MessagePack array if it has sequential numeric keys, starting from 0 and as a MessagePack map otherwise:

$mpArr1 = $packer->pack([1, 2]);               // MP array [1, 2]
$mpArr2 = $packer->pack([0 => 1, 1 => 2]);     // MP array [1, 2]
$mpMap1 = $packer->pack([0 => 1, 2 => 3]);     // MP map {0: 1, 2: 3}
$mpMap2 = $packer->pack([1 => 2, 2 => 3]);     // MP map {1: 2, 2: 3}
$mpMap3 = $packer->pack(['a' => 1, 'b' => 2]); // MP map {a: 1, b: 2}

However, sometimes you need to pack a sequential array as a MessagePack map. To do this, use the packMap method:

$mpMap = $packer->packMap([1, 2]); // {0: 1, 1: 2}

Here is a list of type-specific packing methods:

$packer->packNil();           // MP nil
$packer->packBool(true);      // MP bool
$packer->packInt(42);         // MP int
$packer->packFloat(M_PI);     // MP float (32 or 64)
$packer->packFloat32(M_PI);   // MP float 32
$packer->packFloat64(M_PI);   // MP float 64
$packer->packStr('foo');      // MP str
$packer->packBin("\x80");     // MP bin
$packer->packArray([1, 2]);   // MP array
$packer->packMap(['a' => 1]); // MP map
$packer->packExt(1, "\xaa");  // MP ext

Check the "Custom types" section below on how to pack custom types.

Packing options

The Packer object supports a number of bitmask-based options for fine-tuning the packing process (defaults are in bold):

Name	Description
FORCE_STR	Forces PHP strings to be packed as MessagePack UTF-8 strings
FORCE_BIN	Forces PHP strings to be packed as MessagePack binary data
DETECT_STR_BIN	Detects MessagePack str/bin type automatically
FORCE_ARR	Forces PHP arrays to be packed as MessagePack arrays
FORCE_MAP	Forces PHP arrays to be packed as MessagePack maps
DETECT_ARR_MAP	Detects MessagePack array/map type automatically
FORCE_FLOAT32	Forces PHP floats to be packed as 32-bits MessagePack floats
FORCE_FLOAT64	Forces PHP floats to be packed as 64-bits MessagePack floats

The type detection mode (DETECT_STR_BIN/DETECT_ARR_MAP) adds some overhead which can be noticed when you pack large (16- and 32-bit) arrays or strings. However, if you know the value type in advance (for example, you only work with UTF-8 strings or/and associative arrays), you can eliminate this overhead by forcing the packer to use the appropriate type, which will save it from running the auto-detection routine. Another option is to explicitly specify the value type. The library provides 2 auxiliary classes for this, Map and Bin. Check the "Custom types" section below for details.

Examples:

// detect str/bin type and pack PHP 64-bit floats (doubles) to MP 32-bit floats
$packer = new Packer(PackOptions::DETECT_STR_BIN | PackOptions::FORCE_FLOAT32);

// these will throw MessagePack\Exception\InvalidOptionException
$packer = new Packer(PackOptions::FORCE_STR | PackOptions::FORCE_BIN);
$packer = new Packer(PackOptions::FORCE_FLOAT32 | PackOptions::FORCE_FLOAT64);

Unpacking

To unpack data you can either use an instance of a BufferUnpacker:

$unpacker = new BufferUnpacker();

$unpacker->reset($packed);
$value = $unpacker->unpack();

or call a static method on the MessagePack class:

$value = MessagePack::unpack($packed);

If the packed data is received in chunks (e.g. when reading from a stream), use the tryUnpack method, which attempts to unpack data and returns an array of unpacked messages (if any) instead of throwing an InsufficientDataException:

while ($chunk = ...) {
    $unpacker->append($chunk);
    if ($messages = $unpacker->tryUnpack()) {
        return $messages;
    }
}

If you want to unpack from a specific position in a buffer, use seek:

$unpacker->seek(42); // set position equal to 42 bytes
$unpacker->seek(-8); // set position to 8 bytes before the end of the buffer

To skip bytes from the current position, use skip:

$unpacker->skip(10); // set position to 10 bytes ahead of the current position

To get the number of remaining (unread) bytes in the buffer:

$unreadBytesCount = $unpacker->getRemainingCount();

To check whether the buffer has unread data:

$hasUnreadBytes = $unpacker->hasRemaining();

If needed, you can remove already read data from the buffer by calling:

$releasedBytesCount = $unpacker->release();

With the read method you can read raw (packed) data:

$packedData = $unpacker->read(2); // read 2 bytes

Besides the above methods BufferUnpacker provides type-specific unpacking methods, namely:

$unpacker->unpackNil();   // PHP null
$unpacker->unpackBool();  // PHP bool
$unpacker->unpackInt();   // PHP int
$unpacker->unpackFloat(); // PHP float
$unpacker->unpackStr();   // PHP UTF-8 string
$unpacker->unpackBin();   // PHP binary string
$unpacker->unpackArray(); // PHP sequential array
$unpacker->unpackMap();   // PHP associative array
$unpacker->unpackExt();   // PHP MessagePack\Type\Ext object

Unpacking options

The BufferUnpacker object supports a number of bitmask-based options for fine-tuning the unpacking process (defaults are in bold):

Name	Description
BIGINT_AS_STR	Converts overflowed integers to strings [1]
BIGINT_AS_GMP	Converts overflowed integers to GMP objects [2]
BIGINT_AS_DEC	Converts overflowed integers to Decimal\Decimal objects [3]

1. The binary MessagePack format has unsigned 64-bit as its largest integer data type, but PHP does not support such integers, which means that an overflow can occur during unpacking.

2. Make sure the GMP extension is enabled.

3. Make sure the Decimal extension is enabled.

Examples:

$packedUint64 = "\xcf"."\xff\xff\xff\xff"."\xff\xff\xff\xff";

$unpacker = new BufferUnpacker($packedUint64);
var_dump($unpacker->unpack()); // string(20) "18446744073709551615"

$unpacker = new BufferUnpacker($packedUint64, UnpackOptions::BIGINT_AS_GMP);
var_dump($unpacker->unpack()); // object(GMP) {...}

$unpacker = new BufferUnpacker($packedUint64, UnpackOptions::BIGINT_AS_DEC);
var_dump($unpacker->unpack()); // object(Decimal\Decimal) {...}

Custom types

In addition to the basic types, the library provides functionality to serialize and deserialize arbitrary types. This can be done in several ways, depending on your use case. Let's take a look at them.

Type objects

If you need to serialize an instance of one of your classes into one of the basic MessagePack types, the best way to do this is to implement the CanBePacked interface in the class. A good example of such a class is the Map type class that comes with the library. This type is useful when you want to explicitly specify that a given PHP array should be packed as a MessagePack map without triggering an automatic type detection routine:

$packer = new Packer();

$packedMap = $packer->pack(new Map([1, 2, 3]));
$packedArray = $packer->pack([1, 2, 3]);

More type examples can be found in the src/Type directory.

Type transformers

As with type objects, type transformers are only responsible for serializing values. They should be used when you need to serialize a value that does not implement the CanBePacked interface. Examples of such values could be instances of built-in or third-party classes that you don't own, or non-objects such as resources.

A transformer class must implement the CanPack interface. To use a transformer, it must first be registered in the packer. Here is an example of how to serialize PHP streams into the MessagePack bin format type using one of the supplied transformers, StreamTransformer:

$packer = new Packer(null, [new StreamTransformer()]);

$packedBin = $packer->pack(fopen('/path/to/file', 'r+'));

More type transformer examples can be found in the src/TypeTransformer directory.

Extensions

In contrast to the cases described above, extensions are intended to handle extension types and are responsible for both serialization and deserialization of values (types).

An extension class must implement the Extension interface. To use an extension, it must first be registered in the packer and the unpacker.

The MessagePack specification divides extension types into two groups: predefined and application-specific. Currently, there is only one predefined type in the specification, Timestamp.

Timestamp

The Timestamp extension type is a predefined type. Support for this type in the library is done through the TimestampExtension class. This class is responsible for handling Timestamp objects, which represent the number of seconds and optional adjustment in nanoseconds:

$timestampExtension = new TimestampExtension();

$packer = new Packer();
$packer = $packer->extendWith($timestampExtension);

$unpacker = new BufferUnpacker();
$unpacker = $unpacker->extendWith($timestampExtension);

$packedTimestamp = $packer->pack(Timestamp::now());
$timestamp = $unpacker->reset($packedTimestamp)->unpack();

$seconds = $timestamp->getSeconds();
$nanoseconds = $timestamp->getNanoseconds();

When using the MessagePack class, the Timestamp extension is already registered:

$packedTimestamp = MessagePack::pack(Timestamp::now());
$timestamp = MessagePack::unpack($packedTimestamp);

Application-specific extensions

In addition, the format can be extended with your own types. For example, to make the built-in PHP DateTime objects first-class citizens in your code, you can create a corresponding extension, as shown in the example. Please note, that custom extensions have to be registered with a unique extension ID (an integer from 0 to 127).

More extension examples can be found in the examples/MessagePack directory.

To learn more about how extension types can be useful, check out this article.

Exceptions

If an error occurs during packing/unpacking, a PackingFailedException or an UnpackingFailedException will be thrown, respectively. In addition, an InsufficientDataException can be thrown during unpacking.

An InvalidOptionException will be thrown in case an invalid option (or a combination of mutually exclusive options) is used.

Tests

Run tests as follows:

vendor/bin/phpunit

Also, if you already have Docker installed, you can run the tests in a docker container. First, create a container:

./dockerfile.sh | docker build -t msgpack -

The command above will create a container named msgpack with PHP 8.1 runtime. You may change the default runtime by defining the PHP_IMAGE environment variable:

PHP_IMAGE='php:8.0-cli' ./dockerfile.sh | docker build -t msgpack -

See a list of various images here.

Then run the unit tests:

docker run --rm -v $PWD:/msgpack -w /msgpack msgpack

Fuzzing

To ensure that the unpacking works correctly with malformed/semi-malformed data, you can use a testing technique called Fuzzing. The library ships with a help file (target) for PHP-Fuzzer and can be used as follows:

php-fuzzer fuzz tests/fuzz_buffer_unpacker.php

Performance

To check performance, run:

php -n -dzend_extension=opcache.so \
-dpcre.jit=1 -dopcache.enable=1 -dopcache.enable_cli=1 \
tests/bench.php

Example output

Filter: MessagePack\Tests\Perf\Filter\ListFilter
Rounds: 3
Iterations: 100000

=============================================
Test/Target            Packer  BufferUnpacker
---------------------------------------------
nil .................. 0.0030 ........ 0.0139
false ................ 0.0037 ........ 0.0144
true ................. 0.0040 ........ 0.0137
7-bit uint #1 ........ 0.0052 ........ 0.0120
7-bit uint #2 ........ 0.0059 ........ 0.0114
7-bit uint #3 ........ 0.0061 ........ 0.0119
5-bit sint #1 ........ 0.0067 ........ 0.0126
5-bit sint #2 ........ 0.0064 ........ 0.0132
5-bit sint #3 ........ 0.0066 ........ 0.0135
8-bit uint #1 ........ 0.0078 ........ 0.0200
8-bit uint #2 ........ 0.0077 ........ 0.0212
8-bit uint #3 ........ 0.0086 ........ 0.0203
16-bit uint #1 ....... 0.0111 ........ 0.0271
16-bit uint #2 ....... 0.0115 ........ 0.0260
16-bit uint #3 ....... 0.0103 ........ 0.0273
32-bit uint #1 ....... 0.0116 ........ 0.0326
32-bit uint #2 ....... 0.0118 ........ 0.0332
32-bit uint #3 ....... 0.0127 ........ 0.0325
64-bit uint #1 ....... 0.0140 ........ 0.0277
64-bit uint #2 ....... 0.0134 ........ 0.0294
64-bit uint #3 ....... 0.0134 ........ 0.0281
8-bit int #1 ......... 0.0086 ........ 0.0241
8-bit int #2 ......... 0.0089 ........ 0.0225
8-bit int #3 ......... 0.0085 ........ 0.0229
16-bit int #1 ........ 0.0118 ........ 0.0280
16-bit int #2 ........ 0.0121 ........ 0.0270
16-bit int #3 ........ 0.0109 ........ 0.0274
32-bit int #1 ........ 0.0128 ........ 0.0346
32-bit int #2 ........ 0.0118 ........ 0.0339
32-bit int #3 ........ 0.0135 ........ 0.0368
64-bit int #1 ........ 0.0138 ........ 0.0276
64-bit int #2 ........ 0.0132 ........ 0.0286
64-bit int #3 ........ 0.0137 ........ 0.0274
64-bit int #4 ........ 0.0180 ........ 0.0285
64-bit float #1 ...... 0.0134 ........ 0.0284
64-bit float #2 ...... 0.0125 ........ 0.0275
64-bit float #3 ...... 0.0126 ........ 0.0283
fix string #1 ........ 0.0035 ........ 0.0133
fix string #2 ........ 0.0094 ........ 0.0216
fix string #3 ........ 0.0094 ........ 0.0222
fix string #4 ........ 0.0091 ........ 0.0241
8-bit string #1 ...... 0.0122 ........ 0.0301
8-bit string #2 ...... 0.0118 ........ 0.0304
8-bit string #3 ...... 0.0119 ........ 0.0315
16-bit string #1 ..... 0.0150 ........ 0.0388
16-bit string #2 ..... 0.1545 ........ 0.1665
32-bit string ........ 0.1570 ........ 0.1756
wide char string #1 .. 0.0091 ........ 0.0236
wide char string #2 .. 0.0122 ........ 0.0313
8-bit binary #1 ...... 0.0100 ........ 0.0302
8-bit binary #2 ...... 0.0123 ........ 0.0324
8-bit binary #3 ...... 0.0126 ........ 0.0327
16-bit binary ........ 0.0168 ........ 0.0372
32-bit binary ........ 0.1588 ........ 0.1754
fix array #1 ......... 0.0042 ........ 0.0131
fix array #2 ......... 0.0294 ........ 0.0367
fix array #3 ......... 0.0412 ........ 0.0472
16-bit array #1 ...... 0.1378 ........ 0.1596
16-bit array #2 ........... S ............. S
32-bit array .............. S ............. S
complex array ........ 0.1865 ........ 0.2283
fix map #1 ........... 0.0725 ........ 0.1048
fix map #2 ........... 0.0319 ........ 0.0405
fix map #3 ........... 0.0356 ........ 0.0665
fix map #4 ........... 0.0465 ........ 0.0497
16-bit map #1 ........ 0.2540 ........ 0.3028
16-bit map #2 ............. S ............. S
32-bit map ................ S ............. S
complex map .......... 0.2372 ........ 0.2710
fixext 1 ............. 0.0283 ........ 0.0358
fixext 2 ............. 0.0291 ........ 0.0371
fixext 4 ............. 0.0302 ........ 0.0355
fixext 8 ............. 0.0288 ........ 0.0384
fixext 16 ............ 0.0293 ........ 0.0359
8-bit ext ............ 0.0302 ........ 0.0439
16-bit ext ........... 0.0334 ........ 0.0499
32-bit ext ........... 0.1845 ........ 0.1888
32-bit timestamp #1 .. 0.0337 ........ 0.0547
32-bit timestamp #2 .. 0.0335 ........ 0.0560
64-bit timestamp #1 .. 0.0371 ........ 0.0575
64-bit timestamp #2 .. 0.0374 ........ 0.0542
64-bit timestamp #3 .. 0.0356 ........ 0.0533
96-bit timestamp #1 .. 0.0362 ........ 0.0699
96-bit timestamp #2 .. 0.0381 ........ 0.0701
96-bit timestamp #3 .. 0.0367 ........ 0.0687
=============================================
Total                  2.7618          4.0820
Skipped                     4               4
Failed                      0               0
Ignored                     0               0

With JIT:

php -n -dzend_extension=opcache.so \
-dpcre.jit=1 -dopcache.jit_buffer_size=64M -dopcache.jit=tracing -dopcache.enable=1 -dopcache.enable_cli=1 \
tests/bench.php

Example output

Filter: MessagePack\Tests\Perf\Filter\ListFilter
Rounds: 3
Iterations: 100000

=============================================
Test/Target            Packer  BufferUnpacker
---------------------------------------------
nil .................. 0.0005 ........ 0.0054
false ................ 0.0004 ........ 0.0059
true ................. 0.0004 ........ 0.0059
7-bit uint #1 ........ 0.0010 ........ 0.0047
7-bit uint #2 ........ 0.0010 ........ 0.0046
7-bit uint #3 ........ 0.0010 ........ 0.0046
5-bit sint #1 ........ 0.0025 ........ 0.0046
5-bit sint #2 ........ 0.0023 ........ 0.0046
5-bit sint #3 ........ 0.0024 ........ 0.0045
8-bit uint #1 ........ 0.0043 ........ 0.0081
8-bit uint #2 ........ 0.0043 ........ 0.0079
8-bit uint #3 ........ 0.0041 ........ 0.0080
16-bit uint #1 ....... 0.0064 ........ 0.0095
16-bit uint #2 ....... 0.0064 ........ 0.0091
16-bit uint #3 ....... 0.0064 ........ 0.0094
32-bit uint #1 ....... 0.0085 ........ 0.0114
32-bit uint #2 ....... 0.0077 ........ 0.0122
32-bit uint #3 ....... 0.0077 ........ 0.0120
64-bit uint #1 ....... 0.0085 ........ 0.0159
64-bit uint #2 ....... 0.0086 ........ 0.0157
64-bit uint #3 ....... 0.0086 ........ 0.0158
8-bit int #1 ......... 0.0042 ........ 0.0080
8-bit int #2 ......... 0.0042 ........ 0.0080
8-bit int #3 ......... 0.0042 ........ 0.0081
16-bit int #1 ........ 0.0065 ........ 0.0095
16-bit int #2 ........ 0.0065 ........ 0.0090
16-bit int #3 ........ 0.0056 ........ 0.0085
32-bit int #1 ........ 0.0067 ........ 0.0107
32-bit int #2 ........ 0.0066 ........ 0.0106
32-bit int #3 ........ 0.0063 ........ 0.0104
64-bit int #1 ........ 0.0072 ........ 0.0162
64-bit int #2 ........ 0.0073 ........ 0.0174
64-bit int #3 ........ 0.0072 ........ 0.0164
64-bit int #4 ........ 0.0077 ........ 0.0161
64-bit float #1 ...... 0.0053 ........ 0.0135
64-bit float #2 ...... 0.0053 ........ 0.0135
64-bit float #3 ...... 0.0052 ........ 0.0135
fix string #1 ....... -0.0002 ........ 0.0044
fix string #2 ........ 0.0035 ........ 0.0067
fix string #3 ........ 0.0035 ........ 0.0077
fix string #4 ........ 0.0033 ........ 0.0078
8-bit string #1 ...... 0.0059 ........ 0.0110
8-bit string #2 ...... 0.0063 ........ 0.0121
8-bit string #3 ...... 0.0064 ........ 0.0124
16-bit string #1 ..... 0.0099 ........ 0.0146
16-bit string #2 ..... 0.1522 ........ 0.1474
32-bit string ........ 0.1511 ........ 0.1483
wide char string #1 .. 0.0039 ........ 0.0084
wide char string #2 .. 0.0073 ........ 0.0123
8-bit binary #1 ...... 0.0040 ........ 0.0112
8-bit binary #2 ...... 0.0075 ........ 0.0123
8-bit binary #3 ...... 0.0077 ........ 0.0129
16-bit binary ........ 0.0096 ........ 0.0145
32-bit binary ........ 0.1535 ........ 0.1479
fix array #1 ......... 0.0008 ........ 0.0061
fix array #2 ......... 0.0121 ........ 0.0165
fix array #3 ......... 0.0193 ........ 0.0222
16-bit array #1 ...... 0.0607 ........ 0.0479
16-bit array #2 ........... S ............. S
32-bit array .............. S ............. S
complex array ........ 0.0749 ........ 0.0824
fix map #1 ........... 0.0329 ........ 0.0431
fix map #2 ........... 0.0161 ........ 0.0189
fix map #3 ........... 0.0205 ........ 0.0262
fix map #4 ........... 0.0252 ........ 0.0205
16-bit map #1 ........ 0.1016 ........ 0.0927
16-bit map #2 ............. S ............. S
32-bit map ................ S ............. S
complex map .......... 0.1096 ........ 0.1030
fixext 1 ............. 0.0157 ........ 0.0161
fixext 2 ............. 0.0175 ........ 0.0183
fixext 4 ............. 0.0156 ........ 0.0185
fixext 8 ............. 0.0163 ........ 0.0184
fixext 16 ............ 0.0164 ........ 0.0182
8-bit ext ............ 0.0158 ........ 0.0207
16-bit ext ........... 0.0203 ........ 0.0219
32-bit ext ........... 0.1614 ........ 0.1539
32-bit timestamp #1 .. 0.0195 ........ 0.0249
32-bit timestamp #2 .. 0.0188 ........ 0.0260
64-bit timestamp #1 .. 0.0207 ........ 0.0281
64-bit timestamp #2 .. 0.0212 ........ 0.0291
64-bit timestamp #3 .. 0.0207 ........ 0.0295
96-bit timestamp #1 .. 0.0222 ........ 0.0358
96-bit timestamp #2 .. 0.0228 ........ 0.0353
96-bit timestamp #3 .. 0.0210 ........ 0.0319
=============================================
Total                  1.6432          1.9674
Skipped                     4               4
Failed                      0               0
Ignored                     0               0

You may change default benchmark settings by defining the following environment variables:

Name	Default
MP_BENCH_TARGETS	pure_p,pure_u, see a list of available targets
MP_BENCH_ITERATIONS	100_000
MP_BENCH_DURATION	not set
MP_BENCH_ROUNDS	3
MP_BENCH_TESTS	-@slow, see a list of available tests

For example:

export MP_BENCH_TARGETS=pure_p
export MP_BENCH_ITERATIONS=1000000
export MP_BENCH_ROUNDS=5
# a comma separated list of test names
export MP_BENCH_TESTS='complex array, complex map'
# or a group name
# export MP_BENCH_TESTS='-@slow' // @pecl_comp
# or a regexp
# export MP_BENCH_TESTS='/complex (array|map)/'

Another example, benchmarking both the library and the PECL extension:

MP_BENCH_TARGETS=pure_p,pure_u,pecl_p,pecl_u \
php -n -dextension=msgpack.so -dzend_extension=opcache.so \
-dpcre.jit=1 -dopcache.enable=1 -dopcache.enable_cli=1 \
tests/bench.php

Example output

Filter: MessagePack\Tests\Perf\Filter\ListFilter
Rounds: 3
Iterations: 100000

===========================================================================
Test/Target            Packer  BufferUnpacker  msgpack_pack  msgpack_unpack
---------------------------------------------------------------------------
nil .................. 0.0031 ........ 0.0141 ...... 0.0055 ........ 0.0064
false ................ 0.0039 ........ 0.0154 ...... 0.0056 ........ 0.0053
true ................. 0.0038 ........ 0.0139 ...... 0.0056 ........ 0.0044
7-bit uint #1 ........ 0.0061 ........ 0.0110 ...... 0.0059 ........ 0.0046
7-bit uint #2 ........ 0.0065 ........ 0.0119 ...... 0.0042 ........ 0.0029
7-bit uint #3 ........ 0.0054 ........ 0.0117 ...... 0.0045 ........ 0.0025
5-bit sint #1 ........ 0.0047 ........ 0.0103 ...... 0.0038 ........ 0.0022
5-bit sint #2 ........ 0.0048 ........ 0.0117 ...... 0.0038 ........ 0.0022
5-bit sint #3 ........ 0.0046 ........ 0.0102 ...... 0.0038 ........ 0.0023
8-bit uint #1 ........ 0.0063 ........ 0.0174 ...... 0.0039 ........ 0.0031
8-bit uint #2 ........ 0.0063 ........ 0.0167 ...... 0.0040 ........ 0.0029
8-bit uint #3 ........ 0.0063 ........ 0.0168 ...... 0.0039 ........ 0.0030
16-bit uint #1 ....... 0.0092 ........ 0.0222 ...... 0.0049 ........ 0.0030
16-bit uint #2 ....... 0.0096 ........ 0.0227 ...... 0.0042 ........ 0.0046
16-bit uint #3 ....... 0.0123 ........ 0.0274 ...... 0.0059 ........ 0.0051
32-bit uint #1 ....... 0.0136 ........ 0.0331 ...... 0.0060 ........ 0.0048
32-bit uint #2 ....... 0.0130 ........ 0.0336 ...... 0.0070 ........ 0.0048
32-bit uint #3 ....... 0.0127 ........ 0.0329 ...... 0.0051 ........ 0.0048
64-bit uint #1 ....... 0.0126 ........ 0.0268 ...... 0.0055 ........ 0.0049
64-bit uint #2 ....... 0.0135 ........ 0.0281 ...... 0.0052 ........ 0.0046
64-bit uint #3 ....... 0.0131 ........ 0.0274 ...... 0.0069 ........ 0.0044
8-bit int #1 ......... 0.0077 ........ 0.0236 ...... 0.0058 ........ 0.0044
8-bit int #2 ......... 0.0087 ........ 0.0244 ...... 0.0058 ........ 0.0048
8-bit int #3 ......... 0.0084 ........ 0.0241 ...... 0.0055 ........ 0.0049
16-bit int #1 ........ 0.0112 ........ 0.0271 ...... 0.0048 ........ 0.0045
16-bit int #2 ........ 0.0124 ........ 0.0292 ...... 0.0057 ........ 0.0049
16-bit int #3 ........ 0.0118 ........ 0.0270 ...... 0.0058 ........ 0.0050
32-bit int #1 ........ 0.0137 ........ 0.0366 ...... 0.0058 ........ 0.0051
32-bit int #2 ........ 0.0133 ........ 0.0366 ...... 0.0056 ........ 0.0049
32-bit int #3 ........ 0.0129 ........ 0.0350 ...... 0.0052 ........ 0.0048
64-bit int #1 ........ 0.0145 ........ 0.0254 ...... 0.0034 ........ 0.0025
64-bit int #2 ........ 0.0097 ........ 0.0214 ...... 0.0034 ........ 0.0025
64-bit int #3 ........ 0.0096 ........ 0.0287 ...... 0.0059 ........ 0.0050
64-bit int #4 ........ 0.0143 ........ 0.0277 ...... 0.0059 ........ 0.0046
64-bit float #1 ...... 0.0134 ........ 0.0281 ...... 0.0057 ........ 0.0052
64-bit float #2 ...... 0.0141 ........ 0.0281 ...... 0.0057 ........ 0.0050
64-bit float #3 ...... 0.0144 ........ 0.0282 ...... 0.0057 ........ 0.0050
fix string #1 ........ 0.0036 ........ 0.0143 ...... 0.0066 ........ 0.0053
fix string #2 ........ 0.0107 ........ 0.0222 ...... 0.0065 ........ 0.0068
fix string #3 ........ 0.0116 ........ 0.0245 ...... 0.0063 ........ 0.0069
fix string #4 ........ 0.0105 ........ 0.0253 ...... 0.0083 ........ 0.0077
8-bit string #1 ...... 0.0126 ........ 0.0318 ...... 0.0075 ........ 0.0088
8-bit string #2 ...... 0.0121 ........ 0.0295 ...... 0.0076 ........ 0.0086
8-bit string #3 ...... 0.0125 ........ 0.0293 ...... 0.0130 ........ 0.0093
16-bit string #1 ..... 0.0159 ........ 0.0368 ...... 0.0117 ........ 0.0086
16-bit string #2 ..... 0.1547 ........ 0.1686 ...... 0.1516 ........ 0.1373
32-bit string ........ 0.1558 ........ 0.1729 ...... 0.1511 ........ 0.1396
wide char string #1 .. 0.0098 ........ 0.0237 ...... 0.0066 ........ 0.0065
wide char string #2 .. 0.0128 ........ 0.0291 ...... 0.0061 ........ 0.0082
8-bit binary #1 ........... I ............. I ........... F ............. I
8-bit binary #2 ........... I ............. I ........... F ............. I
8-bit binary #3 ........... I ............. I ........... F ............. I
16-bit binary ............. I ............. I ........... F ............. I
32-bit binary ............. I ............. I ........... F ............. I
fix array #1 ......... 0.0040 ........ 0.0129 ...... 0.0120 ........ 0.0058
fix array #2 ......... 0.0279 ........ 0.0390 ...... 0.0143 ........ 0.0165
fix array #3 ......... 0.0415 ........ 0.0463 ...... 0.0162 ........ 0.0187
16-bit array #1 ...... 0.1349 ........ 0.1628 ...... 0.0334 ........ 0.0341
16-bit array #2 ........... S ............. S ........... S ............. S
32-bit array .............. S ............. S ........... S ............. S
complex array ............. I ............. I ........... F ............. F
fix map #1 ................ I ............. I ........... F ............. I
fix map #2 ........... 0.0345 ........ 0.0391 ...... 0.0143 ........ 0.0168
fix map #3 ................ I ............. I ........... F ............. I
fix map #4 ........... 0.0459 ........ 0.0473 ...... 0.0151 ........ 0.0163
16-bit map #1 ........ 0.2518 ........ 0.2962 ...... 0.0400 ........ 0.0490
16-bit map #2 ............. S ............. S ........... S ............. S
32-bit map ................ S ............. S ........... S ............. S
complex map .......... 0.2380 ........ 0.2682 ...... 0.0545 ........ 0.0579
fixext 1 .................. I ............. I ........... F ............. F
fixext 2 .................. I ............. I ........... F ............. F
fixext 4 .................. I ............. I ........... F ............. F
fixext 8 .................. I ............. I ........... F ............. F
fixext 16 ................. I ............. I ........... F ............. F
8-bit ext ................. I ............. I ........... F ............. F
16-bit ext ................ I ............. I ........... F ............. F
32-bit ext ................ I ............. I ........... F ............. F
32-bit timestamp #1 ....... I ............. I ........... F ............. F
32-bit timestamp #2 ....... I ............. I ........... F ............. F
64-bit timestamp #1 ....... I ............. I ........... F ............. F
64-bit timestamp #2 ....... I ............. I ........... F ............. F
64-bit timestamp #3 ....... I ............. I ........... F ............. F
96-bit timestamp #1 ....... I ............. I ........... F ............. F
96-bit timestamp #2 ....... I ............. I ........... F ............. F
96-bit timestamp #3 ....... I ............. I ........... F ............. F
===========================================================================
Total                  1.5625          2.3866        0.7735          0.7243
Skipped                     4               4             4               4
Failed                      0               0            24              17
Ignored                    24              24             0               7

With JIT:

MP_BENCH_TARGETS=pure_p,pure_u,pecl_p,pecl_u \
php -n -dextension=msgpack.so -dzend_extension=opcache.so \
-dpcre.jit=1 -dopcache.jit_buffer_size=64M -dopcache.jit=tracing -dopcache.enable=1 -dopcache.enable_cli=1 \
tests/bench.php

Example output

Filter: MessagePack\Tests\Perf\Filter\ListFilter
Rounds: 3
Iterations: 100000

===========================================================================
Test/Target            Packer  BufferUnpacker  msgpack_pack  msgpack_unpack
---------------------------------------------------------------------------
nil .................. 0.0001 ........ 0.0052 ...... 0.0053 ........ 0.0042
false ................ 0.0007 ........ 0.0060 ...... 0.0057 ........ 0.0043
true ................. 0.0008 ........ 0.0060 ...... 0.0056 ........ 0.0041
7-bit uint #1 ........ 0.0031 ........ 0.0046 ...... 0.0062 ........ 0.0041
7-bit uint #2 ........ 0.0021 ........ 0.0043 ...... 0.0062 ........ 0.0041
7-bit uint #3 ........ 0.0022 ........ 0.0044 ...... 0.0061 ........ 0.0040
5-bit sint #1 ........ 0.0030 ........ 0.0048 ...... 0.0062 ........ 0.0040
5-bit sint #2 ........ 0.0032 ........ 0.0046 ...... 0.0062 ........ 0.0040
5-bit sint #3 ........ 0.0031 ........ 0.0046 ...... 0.0062 ........ 0.0040
8-bit uint #1 ........ 0.0054 ........ 0.0079 ...... 0.0062 ........ 0.0050
8-bit uint #2 ........ 0.0051 ........ 0.0079 ...... 0.0064 ........ 0.0044
8-bit uint #3 ........ 0.0051 ........ 0.0082 ...... 0.0062 ........ 0.0044
16-bit uint #1 ....... 0.0077 ........ 0.0094 ...... 0.0065 ........ 0.0045
16-bit uint #2 ....... 0.0077 ........ 0.0094 ...... 0.0063 ........ 0.0045
16-bit uint #3 ....... 0.0077 ........ 0.0095 ...... 0.0064 ........ 0.0047
32-bit uint #1 ....... 0.0088 ........ 0.0119 ...... 0.0063 ........ 0.0043
32-bit uint #2 ....... 0.0089 ........ 0.0117 ...... 0.0062 ........ 0.0039
32-bit uint #3 ....... 0.0089 ........ 0.0118 ...... 0.0063 ........ 0.0044
64-bit uint #1 ....... 0.0097 ........ 0.0155 ...... 0.0063 ........ 0.0045
64-bit uint #2 ....... 0.0095 ........ 0.0153 ...... 0.0061 ........ 0.0045
64-bit uint #3 ....... 0.0096 ........ 0.0156 ...... 0.0063 ........ 0.0047
8-bit int #1 ......... 0.0053 ........ 0.0083 ...... 0.0062 ........ 0.0044
8-bit int #2 ......... 0.0052 ........ 0.0080 ...... 0.0062 ........ 0.0044
8-bit int #3 ......... 0.0052 ........ 0.0080 ...... 0.0062 ........ 0.0043
16-bit int #1 ........ 0.0089 ........ 0.0097 ...... 0.0069 ........ 0.0046
16-bit int #2 ........ 0.0075 ........ 0.0093 ...... 0.0063 ........ 0.0043
16-bit int #3 ........ 0.0075 ........ 0.0094 ...... 0.0062 ........ 0.0046
32-bit int #1 ........ 0.0086 ........ 0.0122 ...... 0.0063 ........ 0.0044
32-bit int #2 ........ 0.0087 ........ 0.0120 ...... 0.0066 ........ 0.0046
32-bit int #3 ........ 0.0086 ........ 0.0121 ...... 0.0060 ........ 0.0044
64-bit int #1 ........ 0.0096 ........ 0.0149 ...... 0.0060 ........ 0.0045
64-bit int #2 ........ 0.0096 ........ 0.0157 ...... 0.0062 ........ 0.0044
64-bit int #3 ........ 0.0096 ........ 0.0160 ...... 0.0063 ........ 0.0046
64-bit int #4 ........ 0.0097 ........ 0.0157 ...... 0.0061 ........ 0.0044
64-bit float #1 ...... 0.0079 ........ 0.0153 ...... 0.0056 ........ 0.0044
64-bit float #2 ...... 0.0079 ........ 0.0152 ...... 0.0057 ........ 0.0045
64-bit float #3 ...... 0.0079 ........ 0.0155 ...... 0.0057 ........ 0.0044
fix string #1 ........ 0.0010 ........ 0.0045 ...... 0.0071 ........ 0.0044
fix string #2 ........ 0.0048 ........ 0.0075 ...... 0.0070 ........ 0.0060
fix string #3 ........ 0.0048 ........ 0.0086 ...... 0.0068 ........ 0.0060
fix string #4 ........ 0.0050 ........ 0.0088 ...... 0.0070 ........ 0.0059
8-bit string #1 ...... 0.0081 ........ 0.0129 ...... 0.0069 ........ 0.0062
8-bit string #2 ...... 0.0086 ........ 0.0128 ...... 0.0069 ........ 0.0065
8-bit string #3 ...... 0.0086 ........ 0.0126 ...... 0.0115 ........ 0.0065
16-bit string #1 ..... 0.0105 ........ 0.0137 ...... 0.0128 ........ 0.0068
16-bit string #2 ..... 0.1510 ........ 0.1486 ...... 0.1526 ........ 0.1391
32-bit string ........ 0.1517 ........ 0.1475 ...... 0.1504 ........ 0.1370
wide char string #1 .. 0.0044 ........ 0.0085 ...... 0.0067 ........ 0.0057
wide char string #2 .. 0.0081 ........ 0.0125 ...... 0.0069 ........ 0.0063
8-bit binary #1 ........... I ............. I ........... F ............. I
8-bit binary #2 ........... I ............. I ........... F ............. I
8-bit binary #3 ........... I ............. I ........... F ............. I
16-bit binary ............. I ............. I ........... F ............. I
32-bit binary ............. I ............. I ........... F ............. I
fix array #1 ......... 0.0014 ........ 0.0059 ...... 0.0132 ........ 0.0055
fix array #2 ......... 0.0146 ........ 0.0156 ...... 0.0155 ........ 0.0148
fix array #3 ......... 0.0211 ........ 0.0229 ...... 0.0179 ........ 0.0180
16-bit array #1 ...... 0.0673 ........ 0.0498 ...... 0.0343 ........ 0.0388
16-bit array #2 ........... S ............. S ........... S ............. S
32-bit array .............. S ............. S ........... S ............. S
complex array ............. I ............. I ........... F ............. F
fix map #1 ................ I ............. I ........... F ............. I
fix map #2 ........... 0.0148 ........ 0.0180 ...... 0.0156 ........ 0.0179
fix map #3 ................ I ............. I ........... F ............. I
fix map #4 ........... 0.0252 ........ 0.0201 ...... 0.0214 ........ 0.0167
16-bit map #1 ........ 0.1027 ........ 0.0836 ...... 0.0388 ........ 0.0510
16-bit map #2 ............. S ............. S ........... S ............. S
32-bit map ................ S ............. S ........... S ............. S
complex map .......... 0.1104 ........ 0.1010 ...... 0.0556 ........ 0.0602
fixext 1 .................. I ............. I ........... F ............. F
fixext 2 .................. I ............. I ........... F ............. F
fixext 4 .................. I ............. I ........... F ............. F
fixext 8 .................. I ............. I ........... F ............. F
fixext 16 ................. I ............. I ........... F ............. F
8-bit ext ................. I ............. I ........... F ............. F
16-bit ext ................ I ............. I ........... F ............. F
32-bit ext ................ I ............. I ........... F ............. F
32-bit timestamp #1 ....... I ............. I ........... F ............. F
32-bit timestamp #2 ....... I ............. I ........... F ............. F
64-bit timestamp #1 ....... I ............. I ........... F ............. F
64-bit timestamp #2 ....... I ............. I ........... F ............. F
64-bit timestamp #3 ....... I ............. I ........... F ............. F
96-bit timestamp #1 ....... I ............. I ........... F ............. F
96-bit timestamp #2 ....... I ............. I ........... F ............. F
96-bit timestamp #3 ....... I ............. I ........... F ............. F
===========================================================================
Total                  0.9642          1.0909        0.8224          0.7213
Skipped                     4               4             4               4
Failed                      0               0            24              17
Ignored                    24              24             0               7

Note that the msgpack extension (v2.1.2) doesn't support ext, bin and UTF-8 str types.

License

The library is released under the MIT License. See the bundled LICENSE file for details.

Author: rybakit
Source Code: https://github.com/rybakit/msgpack.php
License: MIT License

#php 

Plpgsql Check: Extension That Allows to Check Plpgsql Source Code.

plpgsql_check

I founded this project, because I wanted to publish the code I wrote in the last two years, when I tried to write enhanced checking for PostgreSQL upstream. It was not fully successful - integration into upstream requires some larger plpgsql refactoring - probably it will not be done in next years (now is Dec 2013). But written code is fully functional and can be used in production (and it is used in production). So, I created this extension to be available for all plpgsql developers.

If you like it and if you would to join to development of this extension, register yourself to postgresql extension hacking google group.

Features

• check fields of referenced database objects and types inside embedded SQL
• using correct types of function parameters
• unused variables and function argumens, unmodified OUT argumens
• partially detection of dead code (due RETURN command)
• detection of missing RETURN command in function
• try to identify unwanted hidden casts, that can be performance issue like unused indexes
• possibility to collect relations and functions used by function
• possibility to check EXECUTE stmt agaist SQL injection vulnerability

I invite any ideas, patches, bugreports.

plpgsql_check is next generation of plpgsql_lint. It allows to check source code by explicit call plpgsql_check_function.

PostgreSQL PostgreSQL 10, 11, 12, 13 and 14 are supported.

The SQL statements inside PL/pgSQL functions are checked by validator for semantic errors. These errors can be found by plpgsql_check_function:

Active mode

postgres=# CREATE EXTENSION plpgsql_check;
LOAD
postgres=# CREATE TABLE t1(a int, b int);
CREATE TABLE

postgres=#
CREATE OR REPLACE FUNCTION public.f1()
RETURNS void
LANGUAGE plpgsql
AS $function$
DECLARE r record;
BEGIN
  FOR r IN SELECT * FROM t1
  LOOP
    RAISE NOTICE '%', r.c; -- there is bug - table t1 missing "c" column
  END LOOP;
END;
$function$;

CREATE FUNCTION

postgres=# select f1(); -- execution doesn't find a bug due to empty table t1
  f1 
 ────
   
 (1 row)

postgres=# \x
Expanded display is on.
postgres=# select * from plpgsql_check_function_tb('f1()');
─[ RECORD 1 ]───────────────────────────
functionid │ f1
lineno     │ 6
statement  │ RAISE
sqlstate   │ 42703
message    │ record "r" has no field "c"
detail     │ [null]
hint       │ [null]
level      │ error
position   │ 0
query      │ [null]

postgres=# \sf+ f1
    CREATE OR REPLACE FUNCTION public.f1()
     RETURNS void
     LANGUAGE plpgsql
1       AS $function$
2       DECLARE r record;
3       BEGIN
4         FOR r IN SELECT * FROM t1
5         LOOP
6           RAISE NOTICE '%', r.c; -- there is bug - table t1 missing "c" column
7         END LOOP;
8       END;
9       $function$

Function plpgsql_check_function() has three possible formats: text, json or xml

select * from plpgsql_check_function('f1()', fatal_errors := false);
                         plpgsql_check_function                         
------------------------------------------------------------------------
 error:42703:4:SQL statement:column "c" of relation "t1" does not exist
 Query: update t1 set c = 30
 --                   ^
 error:42P01:7:RAISE:missing FROM-clause entry for table "r"
 Query: SELECT r.c
 --            ^
 error:42601:7:RAISE:too few parameters specified for RAISE
(7 rows)

postgres=# select * from plpgsql_check_function('fx()', format:='xml');
                 plpgsql_check_function                     
────────────────────────────────────────────────────────────────
 <Function oid="16400">                                        ↵
   <Issue>                                                     ↵
     <Level>error</level>                                      ↵
     <Sqlstate>42P01</Sqlstate>                                ↵
     <Message>relation "foo111" does not exist</Message>       ↵
     <Stmt lineno="3">RETURN</Stmt>                            ↵
     <Query position="23">SELECT (select a from foo111)</Query>↵
   </Issue>                                                    ↵
  </Function>
 (1 row)

Arguments

You can set level of warnings via function's parameters:

Mandatory arguments

• function name or function signature - these functions requires function specification. Any function in PostgreSQL can be specified by Oid or by name or by signature. When you know oid or complete function's signature, you can use a regprocedure type parameter like 'fx()'::regprocedure or 16799::regprocedure. Possible alternative is using a name only, when function's name is unique - like 'fx'. When the name is not unique or the function doesn't exists it raises a error.

Optional arguments

relid DEFAULT 0 - oid of relation assigned with trigger function. It is necessary for check of any trigger function.

fatal_errors boolean DEFAULT true - stop on first error

other_warnings boolean DEFAULT true - show warnings like different attributes number in assignmenet on left and right side, variable overlaps function's parameter, unused variables, unwanted casting, ..

extra_warnings boolean DEFAULT true - show warnings like missing RETURN, shadowed variables, dead code, never read (unused) function's parameter, unmodified variables, modified auto variables, ..

performance_warnings boolean DEFAULT false - performance related warnings like declared type with type modificator, casting, implicit casts in where clause (can be reason why index is not used), ..

security_warnings boolean DEFAULT false - security related checks like SQL injection vulnerability detection

anyelementtype regtype DEFAULT 'int' - a real type used instead anyelement type

anyenumtype regtype DEFAULT '-' - a real type used instead anyenum type

anyrangetype regtype DEFAULT 'int4range' - a real type used instead anyrange type

anycompatibletype DEFAULT 'int' - a real type used instead anycompatible type

anycompatiblerangetype DEFAULT 'int4range' - a real type used instead anycompatible range type

without_warnings DEFAULT false - disable all warnings

all_warnings DEFAULT false - enable all warnings

newtable DEFAULT NULL, oldtable DEFAULT NULL - the names of NEW or OLD transitive tables. These parameters are required when transitive tables are used.

Triggers

When you want to check any trigger, you have to enter a relation that will be used together with trigger function

CREATE TABLE bar(a int, b int);

postgres=# \sf+ foo_trg
    CREATE OR REPLACE FUNCTION public.foo_trg()
         RETURNS trigger
         LANGUAGE plpgsql
1       AS $function$
2       BEGIN
3         NEW.c := NEW.a + NEW.b;
4         RETURN NEW;
5       END;
6       $function$

Missing relation specification

postgres=# select * from plpgsql_check_function('foo_trg()');
ERROR:  missing trigger relation
HINT:  Trigger relation oid must be valid

Correct trigger checking (with specified relation)

postgres=# select * from plpgsql_check_function('foo_trg()', 'bar');
                 plpgsql_check_function                 
--------------------------------------------------------
 error:42703:3:assignment:record "new" has no field "c"
(1 row)

For triggers with transitive tables you can set a oldtable or newtable parameters:

create or replace function footab_trig_func()
returns trigger as $$
declare x int;
begin
  if false then
    -- should be ok;
    select count(*) from newtab into x; 

    -- should fail;
    select count(*) from newtab where d = 10 into x;
  end if;
  return null;
end;
$$ language plpgsql;

select * from plpgsql_check_function('footab_trig_func','footab', newtable := 'newtab');

Mass check

You can use the plpgsql_check_function for mass check functions and mass check triggers. Please, test following queries:

-- check all nontrigger plpgsql functions
SELECT p.oid, p.proname, plpgsql_check_function(p.oid)
   FROM pg_catalog.pg_namespace n
   JOIN pg_catalog.pg_proc p ON pronamespace = n.oid
   JOIN pg_catalog.pg_language l ON p.prolang = l.oid
  WHERE l.lanname = 'plpgsql' AND p.prorettype <> 2279;

or

SELECT p.proname, tgrelid::regclass, cf.*
   FROM pg_proc p
        JOIN pg_trigger t ON t.tgfoid = p.oid 
        JOIN pg_language l ON p.prolang = l.oid
        JOIN pg_namespace n ON p.pronamespace = n.oid,
        LATERAL plpgsql_check_function(p.oid, t.tgrelid) cf
  WHERE n.nspname = 'public' and l.lanname = 'plpgsql'

or

-- check all plpgsql functions (functions or trigger functions with defined triggers)
SELECT
    (pcf).functionid::regprocedure, (pcf).lineno, (pcf).statement,
    (pcf).sqlstate, (pcf).message, (pcf).detail, (pcf).hint, (pcf).level,
    (pcf)."position", (pcf).query, (pcf).context
FROM
(
    SELECT
        plpgsql_check_function_tb(pg_proc.oid, COALESCE(pg_trigger.tgrelid, 0)) AS pcf
    FROM pg_proc
    LEFT JOIN pg_trigger
        ON (pg_trigger.tgfoid = pg_proc.oid)
    WHERE
        prolang = (SELECT lang.oid FROM pg_language lang WHERE lang.lanname = 'plpgsql') AND
        pronamespace <> (SELECT nsp.oid FROM pg_namespace nsp WHERE nsp.nspname = 'pg_catalog') AND
        -- ignore unused triggers
        (pg_proc.prorettype <> (SELECT typ.oid FROM pg_type typ WHERE typ.typname = 'trigger') OR
         pg_trigger.tgfoid IS NOT NULL)
    OFFSET 0
) ss
ORDER BY (pcf).functionid::regprocedure::text, (pcf).lineno

Passive mode

Functions should be checked on start - plpgsql_check module must be loaded.

Configuration

plpgsql_check.mode = [ disabled | by_function | fresh_start | every_start ]
plpgsql_check.fatal_errors = [ yes | no ]

plpgsql_check.show_nonperformance_warnings = false
plpgsql_check.show_performance_warnings = false

Default mode is by_function, that means that the enhanced check is done only in active mode - by plpgsql_check_function. fresh_start means cold start.

You can enable passive mode by

load 'plpgsql'; -- 1.1 and higher doesn't need it
load 'plpgsql_check';
set plpgsql_check.mode = 'every_start';

SELECT fx(10); -- run functions - function is checked before runtime starts it

Limits

plpgsql_check should find almost all errors on really static code. When developer use some PLpgSQL's dynamic features like dynamic SQL or record data type, then false positives are possible. These should be rare - in well written code - and then the affected function should be redesigned or plpgsql_check should be disabled for this function.

CREATE OR REPLACE FUNCTION f1()
RETURNS void AS $$
DECLARE r record;
BEGIN
  FOR r IN EXECUTE 'SELECT * FROM t1'
  LOOP
    RAISE NOTICE '%', r.c;
  END LOOP;
END;
$$ LANGUAGE plpgsql SET plpgsql.enable_check TO false;

A usage of plpgsql_check adds a small overhead (in enabled passive mode) and you should use it only in develop or preprod environments.

Dynamic SQL

This module doesn't check queries that are assembled in runtime. It is not possible to identify results of dynamic queries - so plpgsql_check cannot to set correct type to record variables and cannot to check a dependent SQLs and expressions.

When type of record's variable is not know, you can assign it explicitly with pragma type:

DECLARE r record;
BEGIN
  EXECUTE format('SELECT * FROM %I', _tablename) INTO r;
  PERFORM plpgsql_check_pragma('type: r (id int, processed bool)');
  IF NOT r.processed THEN
    ...

Attention: The SQL injection check can detect only some SQL injection vulnerabilities. This tool cannot be used for security audit! Some issues should not be detected. This check can raise false alarms too - probably when variable is sanitized by other command or when value is of some compose type. 

Refcursors

plpgsql_check should not to detect structure of referenced cursors. A reference on cursor in PLpgSQL is implemented as name of global cursor. In check time, the name is not known (not in all possibilities), and global cursor doesn't exist. It is significant break for any static analyse. PLpgSQL cannot to set correct type for record variables and cannot to check a dependent SQLs and expressions. A solution is same like dynamic SQL. Don't use record variable as target when you use refcursor type or disable plpgsql_check for these functions.

CREATE OR REPLACE FUNCTION foo(refcur_var refcursor)
RETURNS void AS $$
DECLARE
  rec_var record;
BEGIN
  FETCH refcur_var INTO rec_var; -- this is STOP for plpgsql_check
  RAISE NOTICE '%', rec_var;     -- record rec_var is not assigned yet error

In this case a record type should not be used (use known rowtype instead):

CREATE OR REPLACE FUNCTION foo(refcur_var refcursor)
RETURNS void AS $$
DECLARE
  rec_var some_rowtype;
BEGIN
  FETCH refcur_var INTO rec_var;
  RAISE NOTICE '%', rec_var;

Temporary tables

plpgsql_check cannot verify queries over temporary tables that are created in plpgsql's function runtime. For this use case it is necessary to create a fake temp table or disable plpgsql_check for this function.

In reality temp tables are stored in own (per user) schema with higher priority than persistent tables. So you can do (with following trick safetly):

CREATE OR REPLACE FUNCTION public.disable_dml()
RETURNS trigger
LANGUAGE plpgsql AS $function$
BEGIN
  RAISE EXCEPTION SQLSTATE '42P01'
     USING message = format('this instance of %I table doesn''t allow any DML operation', TG_TABLE_NAME),
           hint = format('you should to run "CREATE TEMP TABLE %1$I(LIKE %1$I INCLUDING ALL);" statement',
                         TG_TABLE_NAME);
  RETURN NULL;
END;
$function$;

CREATE TABLE foo(a int, b int); -- doesn't hold data ever
CREATE TRIGGER foo_disable_dml
   BEFORE INSERT OR UPDATE OR DELETE ON foo
   EXECUTE PROCEDURE disable_dml();

postgres=# INSERT INTO  foo VALUES(10,20);
ERROR:  this instance of foo table doesn't allow any DML operation
HINT:  you should to run "CREATE TEMP TABLE foo(LIKE foo INCLUDING ALL);" statement
postgres=# 

CREATE TABLE
postgres=# INSERT INTO  foo VALUES(10,20);
INSERT 0 1

This trick emulates GLOBAL TEMP tables partially and it allows a statical validation. Other possibility is using a [template foreign data wrapper] (https://github.com/okbob/template_fdw)

You can use pragma table and create ephemeral table:

BEGIN
   CREATE TEMP TABLE xxx(a int);
   PERFORM plpgsql_check_pragma('table: xxx(a int)');
   INSERT INTO xxx VALUES(10);

Dependency list

A function plpgsql_show_dependency_tb can show all functions, operators and relations used inside processed function:

postgres=# select * from plpgsql_show_dependency_tb('testfunc(int,float)');
┌──────────┬───────┬────────┬─────────┬────────────────────────────┐
│   type   │  oid  │ schema │  name   │           params           │
╞══════════╪═══════╪════════╪═════════╪════════════════════════════╡
│ FUNCTION │ 36008 │ public │ myfunc1 │ (integer,double precision) │
│ FUNCTION │ 35999 │ public │ myfunc2 │ (integer,double precision) │
│ OPERATOR │ 36007 │ public │ **      │ (integer,integer)          │
│ RELATION │ 36005 │ public │ myview  │                            │
│ RELATION │ 36002 │ public │ mytable │                            │
└──────────┴───────┴────────┴─────────┴────────────────────────────┘
(4 rows)

Profiler

The plpgsql_check contains simple profiler of plpgsql functions and procedures. It can work with/without a access to shared memory. It depends on shared_preload_libraries config. When plpgsql_check was initialized by shared_preload_libraries, then it can allocate shared memory, and function's profiles are stored there. When plpgsql_check cannot to allocate shared momory, the profile is stored in session memory.

Due dependencies, shared_preload_libraries should to contains plpgsql first

postgres=# show shared_preload_libraries ;
┌──────────────────────────┐
│ shared_preload_libraries │
╞══════════════════════════╡
│ plpgsql,plpgsql_check    │
└──────────────────────────┘
(1 row)

The profiler is active when GUC plpgsql_check.profiler is on. The profiler doesn't require shared memory, but if there are not shared memory, then the profile is limmitted just to active session.

When plpgsql_check is initialized by shared_preload_libraries, another GUC is available to configure the amount of shared memory used by the profiler: plpgsql_check.profiler_max_shared_chunks. This defines the maximum number of statements chunk that can be stored in shared memory. For each plpgsql function (or procedure), the whole content is split into chunks of 30 statements. If needed, multiple chunks can be used to store the whole content of a single function. A single chunk is 1704 bytes. The default value for this GUC is 15000, which should be enough for big projects containing hundred of thousands of statements in plpgsql, and will consume about 24MB of memory. If your project doesn't require that much number of chunks, you can set this parameter to a smaller number in order to decrease the memory usage. The minimum value is 50 (which should consume about 83kB of memory), and the maximum value is 100000 (which should consume about 163MB of memory). Changing this parameter requires a PostgreSQL restart.

The profiler will also retrieve the query identifier for each instruction that contains an expression or optimizable statement. Note that this requires pg_stat_statements, or another similar third-party extension), to be installed. There are some limitations to the query identifier retrieval:

• if a plpgsql expression contains underlying statements, only the top level query identifier will be retrieved
• the profiler doesn't compute query identifier by itself but relies on external extension, such as pg_stat_statements, for that. It means that depending on the external extension behavior, you may not be able to see a query identifier for some statements. That's for instance the case with DDL statements, as pg_stat_statements doesn't expose the query identifier for such queries.
• a query identifier is retrieved only for instructions containing expressions. This means that plpgsql_profiler_function_tb() function can report less query identifier than instructions on a single line.

Attention: A update of shared profiles can decrease performance on servers under higher load.

The profile can be displayed by function plpgsql_profiler_function_tb:

postgres=# select lineno, avg_time, source from plpgsql_profiler_function_tb('fx(int)');
┌────────┬──────────┬───────────────────────────────────────────────────────────────────┐
│ lineno │ avg_time │                              source                               │
╞════════╪══════════╪═══════════════════════════════════════════════════════════════════╡
│      1 │          │                                                                   │
│      2 │          │ declare result int = 0;                                           │
│      3 │    0.075 │ begin                                                             │
│      4 │    0.202 │   for i in 1..$1 loop                                             │
│      5 │    0.005 │     select result + i into result; select result + i into result; │
│      6 │          │   end loop;                                                       │
│      7 │        0 │   return result;                                                  │
│      8 │          │ end;                                                              │
└────────┴──────────┴───────────────────────────────────────────────────────────────────┘
(9 rows)

The profile per statements (not per line) can be displayed by function plpgsql_profiler_function_statements_tb:

        CREATE OR REPLACE FUNCTION public.fx1(a integer)
         RETURNS integer
         LANGUAGE plpgsql
1       AS $function$
2       begin
3         if a > 10 then
4           raise notice 'ahoj';
5           return -1;
6         else
7           raise notice 'nazdar';
8           return 1;
9         end if;
10      end;
11      $function$

postgres=# select stmtid, parent_stmtid, parent_note, lineno, exec_stmts, stmtname
             from plpgsql_profiler_function_statements_tb('fx1');
┌────────┬───────────────┬─────────────┬────────┬────────────┬─────────────────┐
│ stmtid │ parent_stmtid │ parent_note │ lineno │ exec_stmts │    stmtname     │
╞════════╪═══════════════╪═════════════╪════════╪════════════╪═════════════════╡
│      0 │             ∅ │ ∅           │      2 │          0 │ statement block │
│      1 │             0 │ body        │      3 │          0 │ IF              │
│      2 │             1 │ then body   │      4 │          0 │ RAISE           │
│      3 │             1 │ then body   │      5 │          0 │ RETURN          │
│      4 │             1 │ else body   │      7 │          0 │ RAISE           │
│      5 │             1 │ else body   │      8 │          0 │ RETURN          │
└────────┴───────────────┴─────────────┴────────┴────────────┴─────────────────┘
(6 rows)

All stored profiles can be displayed by calling function plpgsql_profiler_functions_all:

postgres=# select * from plpgsql_profiler_functions_all();
┌───────────────────────┬────────────┬────────────┬──────────┬─────────────┬──────────┬──────────┐
│        funcoid        │ exec_count │ total_time │ avg_time │ stddev_time │ min_time │ max_time │
╞═══════════════════════╪════════════╪════════════╪══════════╪═════════════╪══════════╪══════════╡
│ fxx(double precision) │          1 │       0.01 │     0.01 │        0.00 │     0.01 │     0.01 │
└───────────────────────┴────────────┴────────────┴──────────┴─────────────┴──────────┴──────────┘
(1 row)

There are two functions for cleaning stored profiles: plpgsql_profiler_reset_all() and plpgsql_profiler_reset(regprocedure).

Coverage metrics

plpgsql_check provides two functions:

• plpgsql_coverage_statements(name)
• plpgsql_coverage_branches(name)

Note

There is another very good PLpgSQL profiler - https://bitbucket.org/openscg/plprofiler

My extension is designed to be simple for use and practical. Nothing more or less.

plprofiler is more complex. It build call graphs and from this graph it can creates flame graph of execution times.

Both extensions can be used together with buildin PostgreSQL's feature - tracking functions.

set track_functions to 'pl';
...
select * from pg_stat_user_functions;

Tracer

plpgsql_check provides a tracing possibility - in this mode you can see notices on start or end functions (terse and default verbosity) and start or end statements (verbose verbosity). For default and verbose verbosity the content of function arguments is displayed. The content of related variables are displayed when verbosity is verbose.

postgres=# do $$ begin perform fx(10,null, 'now', e'stěhule'); end; $$;
NOTICE:  #0 ->> start of inline_code_block (Oid=0)
NOTICE:  #2   ->> start of function fx(integer,integer,date,text) (Oid=16405)
NOTICE:  #2        call by inline_code_block line 1 at PERFORM
NOTICE:  #2       "a" => '10', "b" => null, "c" => '2020-08-03', "d" => 'stěhule'
NOTICE:  #4     ->> start of function fx(integer) (Oid=16404)
NOTICE:  #4          call by fx(integer,integer,date,text) line 1 at PERFORM
NOTICE:  #4         "a" => '10'
NOTICE:  #4     <<- end of function fx (elapsed time=0.098 ms)
NOTICE:  #2   <<- end of function fx (elapsed time=0.399 ms)
NOTICE:  #0 <<- end of block (elapsed time=0.754 ms)

The number after # is a execution frame counter (this number is related to deep of error context stack). It allows to pair start end and of function.

Tracing is enabled by setting plpgsql_check.tracer to on. Attention - enabling this behaviour has significant negative impact on performance (unlike the profiler). You can set a level for output used by tracer plpgsql_check.tracer_errlevel (default is notice). The output content is limited by length specified by plpgsql_check.tracer_variable_max_length configuration variable.

In terse verbose mode the output is reduced:

postgres=# set plpgsql_check.tracer_verbosity TO terse;
SET
postgres=# do $$ begin perform fx(10,null, 'now', e'stěhule'); end; $$;
NOTICE:  #0 start of inline code block (oid=0)
NOTICE:  #2 start of fx (oid=16405)
NOTICE:  #4 start of fx (oid=16404)
NOTICE:  #4 end of fx
NOTICE:  #2 end of fx
NOTICE:  #0 end of inline code block

In verbose mode the output is extended about statement details:

postgres=# do $$ begin perform fx(10,null, 'now', e'stěhule'); end; $$;
NOTICE:  #0            ->> start of block inline_code_block (oid=0)
NOTICE:  #0.1       1  --> start of PERFORM
NOTICE:  #2              ->> start of function fx(integer,integer,date,text) (oid=16405)
NOTICE:  #2                   call by inline_code_block line 1 at PERFORM
NOTICE:  #2                  "a" => '10', "b" => null, "c" => '2020-08-04', "d" => 'stěhule'
NOTICE:  #2.1       1    --> start of PERFORM
NOTICE:  #2.1                "a" => '10'
NOTICE:  #4                ->> start of function fx(integer) (oid=16404)
NOTICE:  #4                     call by fx(integer,integer,date,text) line 1 at PERFORM
NOTICE:  #4                    "a" => '10'
NOTICE:  #4.1       6      --> start of assignment
NOTICE:  #4.1                  "a" => '10', "b" => '20'
NOTICE:  #4.1              <-- end of assignment (elapsed time=0.076 ms)
NOTICE:  #4.1                  "res" => '130'
NOTICE:  #4.2       7      --> start of RETURN
NOTICE:  #4.2                  "res" => '130'
NOTICE:  #4.2              <-- end of RETURN (elapsed time=0.054 ms)
NOTICE:  #4                <<- end of function fx (elapsed time=0.373 ms)
NOTICE:  #2.1            <-- end of PERFORM (elapsed time=0.589 ms)
NOTICE:  #2              <<- end of function fx (elapsed time=0.727 ms)
NOTICE:  #0.1          <-- end of PERFORM (elapsed time=1.147 ms)
NOTICE:  #0            <<- end of block (elapsed time=1.286 ms)

Special feature of tracer is tracing of ASSERT statement when plpgsql_check.trace_assert is on. When plpgsql_check.trace_assert_verbosity is DEFAULT, then all function's or procedure's variables are displayed when assert expression is false. When this configuration is VERBOSE then all variables from all plpgsql frames are displayed. This behaviour is independent on plpgsql.check_asserts value. It can be used, although the assertions are disabled in plpgsql runtime.

postgres=# set plpgsql_check.tracer to off;
postgres=# set plpgsql_check.trace_assert_verbosity TO verbose;

postgres=# do $$ begin perform fx(10,null, 'now', e'stěhule'); end; $$;
NOTICE:  #4 PLpgSQL assert expression (false) on line 12 of fx(integer) is false
NOTICE:   "a" => '10', "res" => null, "b" => '20'
NOTICE:  #2 PL/pgSQL function fx(integer,integer,date,text) line 1 at PERFORM
NOTICE:   "a" => '10', "b" => null, "c" => '2020-08-05', "d" => 'stěhule'
NOTICE:  #0 PL/pgSQL function inline_code_block line 1 at PERFORM
ERROR:  assertion failed
CONTEXT:  PL/pgSQL function fx(integer) line 12 at ASSERT
SQL statement "SELECT fx(a)"
PL/pgSQL function fx(integer,integer,date,text) line 1 at PERFORM
SQL statement "SELECT fx(10,null, 'now', e'stěhule')"
PL/pgSQL function inline_code_block line 1 at PERFORM

postgres=# set plpgsql.check_asserts to off;
SET
postgres=# do $$ begin perform fx(10,null, 'now', e'stěhule'); end; $$;
NOTICE:  #4 PLpgSQL assert expression (false) on line 12 of fx(integer) is false
NOTICE:   "a" => '10', "res" => null, "b" => '20'
NOTICE:  #2 PL/pgSQL function fx(integer,integer,date,text) line 1 at PERFORM
NOTICE:   "a" => '10', "b" => null, "c" => '2020-08-05', "d" => 'stěhule'
NOTICE:  #0 PL/pgSQL function inline_code_block line 1 at PERFORM
DO

Attention - SECURITY

Tracer prints content of variables or function arguments. For security definer function, this content can hold security sensitive data. This is reason why tracer is disabled by default and should be enabled only with super user rights plpgsql_check.enable_tracer.

Pragma

You can configure plpgsql_check behave inside checked function with "pragma" function. This is a analogy of PL/SQL or ADA language of PRAGMA feature. PLpgSQL doesn't support PRAGMA, but plpgsql_check detects function named plpgsql_check_pragma and get options from parameters of this function. These plpgsql_check options are valid to end of group of statements.

CREATE OR REPLACE FUNCTION test()
RETURNS void AS $$
BEGIN
  ...
  -- for following statements disable check
  PERFORM plpgsql_check_pragma('disable:check');
  ...
  -- enable check again
  PERFORM plpgsql_check_pragma('enable:check');
  ...
END;
$$ LANGUAGE plpgsql;

The function plpgsql_check_pragma is immutable function that returns one. It is defined by plpgsql_check extension. You can declare alternative plpgsql_check_pragma function like:

CREATE OR REPLACE FUNCTION plpgsql_check_pragma(VARIADIC args[])
RETURNS int AS $$
SELECT 1
$$ LANGUAGE sql IMMUTABLE;

Using pragma function in declaration part of top block sets options on function level too.

CREATE OR REPLACE FUNCTION test()
RETURNS void AS $$
DECLARE
  aux int := plpgsql_check_pragma('disable:extra_warnings');
  ...

Shorter syntax for pragma is supported too:

CREATE OR REPLACE FUNCTION test()
RETURNS void AS $$
DECLARE r record;
BEGIN
  PERFORM 'PRAGMA:TYPE:r (a int, b int)';
  PERFORM 'PRAGMA:TABLE: x (like pg_class)';
  ...

Supported pragmas

echo:str - print string (for testing)

status:check,status:tracer, status:other_warnings, status:performance_warnings, status:extra_warnings,status:security_warnings

enable:check,enable:tracer, enable:other_warnings, enable:performance_warnings, enable:extra_warnings,enable:security_warnings

disable:check,disable:tracer, disable:other_warnings, disable:performance_warnings, disable:extra_warnings,disable:security_warnings

type:varname typename or type:varname (fieldname type, ...) - set type to variable of record type

table: name (column_name type, ...) or table: name (like tablename) - create ephereal table

Pragmas enable:tracer and disable:tracerare active for Postgres 12 and higher

Compilation

You need a development environment for PostgreSQL extensions:

make clean
make install

result:

[pavel@localhost plpgsql_check]$ make USE_PGXS=1 clean
rm -f plpgsql_check.so   libplpgsql_check.a  libplpgsql_check.pc
rm -f plpgsql_check.o
rm -rf results/ regression.diffs regression.out tmp_check/ log/
[pavel@localhost plpgsql_check]$ make USE_PGXS=1 all
clang -O2 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fpic -I/usr/local/pgsql/lib/pgxs/src/makefiles/../../src/pl/plpgsql/src -I. -I./ -I/usr/local/pgsql/include/server -I/usr/local/pgsql/include/internal -D_GNU_SOURCE   -c -o plpgsql_check.o plpgsql_check.c
clang -O2 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fpic -I/usr/local/pgsql/lib/pgxs/src/makefiles/../../src/pl/plpgsql/src -shared -o plpgsql_check.so plpgsql_check.o -L/usr/local/pgsql/lib -Wl,--as-needed -Wl,-rpath,'/usr/local/pgsql/lib',--enable-new-dtags  
[pavel@localhost plpgsql_check]$ su root
Password: *******
[root@localhost plpgsql_check]# make USE_PGXS=1 install
/usr/bin/mkdir -p '/usr/local/pgsql/lib'
/usr/bin/mkdir -p '/usr/local/pgsql/share/extension'
/usr/bin/mkdir -p '/usr/local/pgsql/share/extension'
/usr/bin/install -c -m 755  plpgsql_check.so '/usr/local/pgsql/lib/plpgsql_check.so'
/usr/bin/install -c -m 644 plpgsql_check.control '/usr/local/pgsql/share/extension/'
/usr/bin/install -c -m 644 plpgsql_check--0.9.sql '/usr/local/pgsql/share/extension/'
[root@localhost plpgsql_check]# exit
[pavel@localhost plpgsql_check]$ make USE_PGXS=1 installcheck
/usr/local/pgsql/lib/pgxs/src/makefiles/../../src/test/regress/pg_regress --inputdir=./ --psqldir='/usr/local/pgsql/bin'    --dbname=pl_regression --load-language=plpgsql --dbname=contrib_regression plpgsql_check_passive plpgsql_check_active plpgsql_check_active-9.5
(using postmaster on Unix socket, default port)
============== dropping database "contrib_regression" ==============
DROP DATABASE
============== creating database "contrib_regression" ==============
CREATE DATABASE
ALTER DATABASE
============== installing plpgsql                     ==============
CREATE LANGUAGE
============== running regression test queries        ==============
test plpgsql_check_passive    ... ok
test plpgsql_check_active     ... ok
test plpgsql_check_active-9.5 ... ok

=====================
 All 3 tests passed. 
=====================

Compilation on Ubuntu

Sometimes successful compilation can require libicu-dev package (PostgreSQL 10 and higher - when pg was compiled with ICU support)

sudo apt install libicu-dev

Compilation plpgsql_check on Windows

You can check precompiled dll libraries http://okbob.blogspot.cz/2015/02/plpgsqlcheck-is-available-for-microsoft.html

or compile by self:

1. Download and install PostgreSQL for Win32 from http://www.enterprisedb.com
2. Download and install Microsoft Visual C++ Express
3. Lern tutorial http://blog.2ndquadrant.com/compiling-postgresql-extensions-visual-studio-windows
4. Build plpgsql_check.dll
5. Install plugin
6. copy plpgsql_check.dll to PostgreSQL\14\lib
7. copy plpgsql_check.control and plpgsql_check--2.1.sql to PostgreSQL\14\share\extension

Checked on

• gcc on Linux (against all supported PostgreSQL)
• clang 3.4 on Linux (against PostgreSQL 10)
• for success regress tests the PostgreSQL 10 or higher is required

Compilation against PostgreSQL 10 requires libICU!

Licence

Copyright (c) Pavel Stehule (pavel.stehule@gmail.com)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Note

If you like it, send a postcard to address

Pavel Stehule
Skalice 12
256 01 Benesov u Prahy
Czech Republic

I invite any questions, comments, bug reports, patches on mail address pavel.stehule@gmail.com

---

Author: okbob
Source Code: https://github.com/okbob/plpgsql_check
License: View license

#postgresql 

Plpgsql Check: Extension That Allows to Check Plpgsql Source Code.

plpgsql_check

I founded this project, because I wanted to publish the code I wrote in the last two years, when I tried to write enhanced checking for PostgreSQL upstream. It was not fully successful - integration into upstream requires some larger plpgsql refactoring - probably it will not be done in next years (now is Dec 2013). But written code is fully functional and can be used in production (and it is used in production). So, I created this extension to be available for all plpgsql developers.

If you like it and if you would to join to development of this extension, register yourself to postgresql extension hacking google group.

Features

• check fields of referenced database objects and types inside embedded SQL
• using correct types of function parameters
• unused variables and function argumens, unmodified OUT argumens
• partially detection of dead code (due RETURN command)
• detection of missing RETURN command in function
• try to identify unwanted hidden casts, that can be performance issue like unused indexes
• possibility to collect relations and functions used by function
• possibility to check EXECUTE stmt agaist SQL injection vulnerability

I invite any ideas, patches, bugreports.

plpgsql_check is next generation of plpgsql_lint. It allows to check source code by explicit call plpgsql_check_function.

PostgreSQL PostgreSQL 10, 11, 12, 13 and 14 are supported.

The SQL statements inside PL/pgSQL functions are checked by validator for semantic errors. These errors can be found by plpgsql_check_function:

Active mode

postgres=# CREATE EXTENSION plpgsql_check;
LOAD
postgres=# CREATE TABLE t1(a int, b int);
CREATE TABLE

postgres=#
CREATE OR REPLACE FUNCTION public.f1()
RETURNS void
LANGUAGE plpgsql
AS $function$
DECLARE r record;
BEGIN
  FOR r IN SELECT * FROM t1
  LOOP
    RAISE NOTICE '%', r.c; -- there is bug - table t1 missing "c" column
  END LOOP;
END;
$function$;

CREATE FUNCTION

postgres=# select f1(); -- execution doesn't find a bug due to empty table t1
  f1 
 ────
   
 (1 row)

postgres=# \x
Expanded display is on.
postgres=# select * from plpgsql_check_function_tb('f1()');
─[ RECORD 1 ]───────────────────────────
functionid │ f1
lineno     │ 6
statement  │ RAISE
sqlstate   │ 42703
message    │ record "r" has no field "c"
detail     │ [null]
hint       │ [null]
level      │ error
position   │ 0
query      │ [null]

postgres=# \sf+ f1
    CREATE OR REPLACE FUNCTION public.f1()
     RETURNS void
     LANGUAGE plpgsql
1       AS $function$
2       DECLARE r record;
3       BEGIN
4         FOR r IN SELECT * FROM t1
5         LOOP
6           RAISE NOTICE '%', r.c; -- there is bug - table t1 missing "c" column
7         END LOOP;
8       END;
9       $function$

Function plpgsql_check_function() has three possible formats: text, json or xml

select * from plpgsql_check_function('f1()', fatal_errors := false);
                         plpgsql_check_function                         
------------------------------------------------------------------------
 error:42703:4:SQL statement:column "c" of relation "t1" does not exist
 Query: update t1 set c = 30
 --                   ^
 error:42P01:7:RAISE:missing FROM-clause entry for table "r"
 Query: SELECT r.c
 --            ^
 error:42601:7:RAISE:too few parameters specified for RAISE
(7 rows)

postgres=# select * from plpgsql_check_function('fx()', format:='xml');
                 plpgsql_check_function                     
────────────────────────────────────────────────────────────────
 <Function oid="16400">                                        ↵
   <Issue>                                                     ↵
     <Level>error</level>                                      ↵
     <Sqlstate>42P01</Sqlstate>                                ↵
     <Message>relation "foo111" does not exist</Message>       ↵
     <Stmt lineno="3">RETURN</Stmt>                            ↵
     <Query position="23">SELECT (select a from foo111)</Query>↵
   </Issue>                                                    ↵
  </Function>
 (1 row)

Arguments

You can set level of warnings via function's parameters:

Mandatory arguments

• function name or function signature - these functions requires function specification. Any function in PostgreSQL can be specified by Oid or by name or by signature. When you know oid or complete function's signature, you can use a regprocedure type parameter like 'fx()'::regprocedure or 16799::regprocedure. Possible alternative is using a name only, when function's name is unique - like 'fx'. When the name is not unique or the function doesn't exists it raises a error.

Optional arguments

relid DEFAULT 0 - oid of relation assigned with trigger function. It is necessary for check of any trigger function.

fatal_errors boolean DEFAULT true - stop on first error

other_warnings boolean DEFAULT true - show warnings like different attributes number in assignmenet on left and right side, variable overlaps function's parameter, unused variables, unwanted casting, ..

extra_warnings boolean DEFAULT true - show warnings like missing RETURN, shadowed variables, dead code, never read (unused) function's parameter, unmodified variables, modified auto variables, ..

performance_warnings boolean DEFAULT false - performance related warnings like declared type with type modificator, casting, implicit casts in where clause (can be reason why index is not used), ..

security_warnings boolean DEFAULT false - security related checks like SQL injection vulnerability detection

anyelementtype regtype DEFAULT 'int' - a real type used instead anyelement type

anyenumtype regtype DEFAULT '-' - a real type used instead anyenum type

anyrangetype regtype DEFAULT 'int4range' - a real type used instead anyrange type

anycompatibletype DEFAULT 'int' - a real type used instead anycompatible type

anycompatiblerangetype DEFAULT 'int4range' - a real type used instead anycompatible range type

without_warnings DEFAULT false - disable all warnings

all_warnings DEFAULT false - enable all warnings

newtable DEFAULT NULL, oldtable DEFAULT NULL - the names of NEW or OLD transitive tables. These parameters are required when transitive tables are used.

Triggers

When you want to check any trigger, you have to enter a relation that will be used together with trigger function

CREATE TABLE bar(a int, b int);

postgres=# \sf+ foo_trg
    CREATE OR REPLACE FUNCTION public.foo_trg()
         RETURNS trigger
         LANGUAGE plpgsql
1       AS $function$
2       BEGIN
3         NEW.c := NEW.a + NEW.b;
4         RETURN NEW;
5       END;
6       $function$

Missing relation specification

postgres=# select * from plpgsql_check_function('foo_trg()');
ERROR:  missing trigger relation
HINT:  Trigger relation oid must be valid

Correct trigger checking (with specified relation)

postgres=# select * from plpgsql_check_function('foo_trg()', 'bar');
                 plpgsql_check_function                 
--------------------------------------------------------
 error:42703:3:assignment:record "new" has no field "c"
(1 row)

For triggers with transitive tables you can set a oldtable or newtable parameters:

create or replace function footab_trig_func()
returns trigger as $$
declare x int;
begin
  if false then
    -- should be ok;
    select count(*) from newtab into x; 

    -- should fail;
    select count(*) from newtab where d = 10 into x;
  end if;
  return null;
end;
$$ language plpgsql;

select * from plpgsql_check_function('footab_trig_func','footab', newtable := 'newtab');

Mass check

You can use the plpgsql_check_function for mass check functions and mass check triggers. Please, test following queries:

-- check all nontrigger plpgsql functions
SELECT p.oid, p.proname, plpgsql_check_function(p.oid)
   FROM pg_catalog.pg_namespace n
   JOIN pg_catalog.pg_proc p ON pronamespace = n.oid
   JOIN pg_catalog.pg_language l ON p.prolang = l.oid
  WHERE l.lanname = 'plpgsql' AND p.prorettype <> 2279;

or

SELECT p.proname, tgrelid::regclass, cf.*
   FROM pg_proc p
        JOIN pg_trigger t ON t.tgfoid = p.oid 
        JOIN pg_language l ON p.prolang = l.oid
        JOIN pg_namespace n ON p.pronamespace = n.oid,
        LATERAL plpgsql_check_function(p.oid, t.tgrelid) cf
  WHERE n.nspname = 'public' and l.lanname = 'plpgsql'

or

-- check all plpgsql functions (functions or trigger functions with defined triggers)
SELECT
    (pcf).functionid::regprocedure, (pcf).lineno, (pcf).statement,
    (pcf).sqlstate, (pcf).message, (pcf).detail, (pcf).hint, (pcf).level,
    (pcf)."position", (pcf).query, (pcf).context
FROM
(
    SELECT
        plpgsql_check_function_tb(pg_proc.oid, COALESCE(pg_trigger.tgrelid, 0)) AS pcf
    FROM pg_proc
    LEFT JOIN pg_trigger
        ON (pg_trigger.tgfoid = pg_proc.oid)
    WHERE
        prolang = (SELECT lang.oid FROM pg_language lang WHERE lang.lanname = 'plpgsql') AND
        pronamespace <> (SELECT nsp.oid FROM pg_namespace nsp WHERE nsp.nspname = 'pg_catalog') AND
        -- ignore unused triggers
        (pg_proc.prorettype <> (SELECT typ.oid FROM pg_type typ WHERE typ.typname = 'trigger') OR
         pg_trigger.tgfoid IS NOT NULL)
    OFFSET 0
) ss
ORDER BY (pcf).functionid::regprocedure::text, (pcf).lineno

Passive mode

Functions should be checked on start - plpgsql_check module must be loaded.

Configuration

plpgsql_check.mode = [ disabled | by_function | fresh_start | every_start ]
plpgsql_check.fatal_errors = [ yes | no ]

plpgsql_check.show_nonperformance_warnings = false
plpgsql_check.show_performance_warnings = false

Default mode is by_function, that means that the enhanced check is done only in active mode - by plpgsql_check_function. fresh_start means cold start.

You can enable passive mode by

load 'plpgsql'; -- 1.1 and higher doesn't need it
load 'plpgsql_check';
set plpgsql_check.mode = 'every_start';

SELECT fx(10); -- run functions - function is checked before runtime starts it

Limits

plpgsql_check should find almost all errors on really static code. When developer use some PLpgSQL's dynamic features like dynamic SQL or record data type, then false positives are possible. These should be rare - in well written code - and then the affected function should be redesigned or plpgsql_check should be disabled for this function.

CREATE OR REPLACE FUNCTION f1()
RETURNS void AS $$
DECLARE r record;
BEGIN
  FOR r IN EXECUTE 'SELECT * FROM t1'
  LOOP
    RAISE NOTICE '%', r.c;
  END LOOP;
END;
$$ LANGUAGE plpgsql SET plpgsql.enable_check TO false;

A usage of plpgsql_check adds a small overhead (in enabled passive mode) and you should use it only in develop or preprod environments.

Dynamic SQL

This module doesn't check queries that are assembled in runtime. It is not possible to identify results of dynamic queries - so plpgsql_check cannot to set correct type to record variables and cannot to check a dependent SQLs and expressions.

When type of record's variable is not know, you can assign it explicitly with pragma type:

DECLARE r record;
BEGIN
  EXECUTE format('SELECT * FROM %I', _tablename) INTO r;
  PERFORM plpgsql_check_pragma('type: r (id int, processed bool)');
  IF NOT r.processed THEN
    ...

Attention: The SQL injection check can detect only some SQL injection vulnerabilities. This tool cannot be used for security audit! Some issues should not be detected. This check can raise false alarms too - probably when variable is sanitized by other command or when value is of some compose type. 

Refcursors

plpgsql_check should not to detect structure of referenced cursors. A reference on cursor in PLpgSQL is implemented as name of global cursor. In check time, the name is not known (not in all possibilities), and global cursor doesn't exist. It is significant break for any static analyse. PLpgSQL cannot to set correct type for record variables and cannot to check a dependent SQLs and expressions. A solution is same like dynamic SQL. Don't use record variable as target when you use refcursor type or disable plpgsql_check for these functions.

CREATE OR REPLACE FUNCTION foo(refcur_var refcursor)
RETURNS void AS $$
DECLARE
  rec_var record;
BEGIN
  FETCH refcur_var INTO rec_var; -- this is STOP for plpgsql_check
  RAISE NOTICE '%', rec_var;     -- record rec_var is not assigned yet error

In this case a record type should not be used (use known rowtype instead):

CREATE OR REPLACE FUNCTION foo(refcur_var refcursor)
RETURNS void AS $$
DECLARE
  rec_var some_rowtype;
BEGIN
  FETCH refcur_var INTO rec_var;
  RAISE NOTICE '%', rec_var;

Temporary tables

plpgsql_check cannot verify queries over temporary tables that are created in plpgsql's function runtime. For this use case it is necessary to create a fake temp table or disable plpgsql_check for this function.

In reality temp tables are stored in own (per user) schema with higher priority than persistent tables. So you can do (with following trick safetly):

CREATE OR REPLACE FUNCTION public.disable_dml()
RETURNS trigger
LANGUAGE plpgsql AS $function$
BEGIN
  RAISE EXCEPTION SQLSTATE '42P01'
     USING message = format('this instance of %I table doesn''t allow any DML operation', TG_TABLE_NAME),
           hint = format('you should to run "CREATE TEMP TABLE %1$I(LIKE %1$I INCLUDING ALL);" statement',
                         TG_TABLE_NAME);
  RETURN NULL;
END;
$function$;

CREATE TABLE foo(a int, b int); -- doesn't hold data ever
CREATE TRIGGER foo_disable_dml
   BEFORE INSERT OR UPDATE OR DELETE ON foo
   EXECUTE PROCEDURE disable_dml();

postgres=# INSERT INTO  foo VALUES(10,20);
ERROR:  this instance of foo table doesn't allow any DML operation
HINT:  you should to run "CREATE TEMP TABLE foo(LIKE foo INCLUDING ALL);" statement
postgres=# 

CREATE TABLE
postgres=# INSERT INTO  foo VALUES(10,20);
INSERT 0 1

This trick emulates GLOBAL TEMP tables partially and it allows a statical validation. Other possibility is using a [template foreign data wrapper] (https://github.com/okbob/template_fdw)

You can use pragma table and create ephemeral table:

BEGIN
   CREATE TEMP TABLE xxx(a int);
   PERFORM plpgsql_check_pragma('table: xxx(a int)');
   INSERT INTO xxx VALUES(10);

Dependency list

A function plpgsql_show_dependency_tb can show all functions, operators and relations used inside processed function:

postgres=# select * from plpgsql_show_dependency_tb('testfunc(int,float)');
┌──────────┬───────┬────────┬─────────┬────────────────────────────┐
│   type   │  oid  │ schema │  name   │           params           │
╞══════════╪═══════╪════════╪═════════╪════════════════════════════╡
│ FUNCTION │ 36008 │ public │ myfunc1 │ (integer,double precision) │
│ FUNCTION │ 35999 │ public │ myfunc2 │ (integer,double precision) │
│ OPERATOR │ 36007 │ public │ **      │ (integer,integer)          │
│ RELATION │ 36005 │ public │ myview  │                            │
│ RELATION │ 36002 │ public │ mytable │                            │
└──────────┴───────┴────────┴─────────┴────────────────────────────┘
(4 rows)

Profiler

The plpgsql_check contains simple profiler of plpgsql functions and procedures. It can work with/without a access to shared memory. It depends on shared_preload_libraries config. When plpgsql_check was initialized by shared_preload_libraries, then it can allocate shared memory, and function's profiles are stored there. When plpgsql_check cannot to allocate shared momory, the profile is stored in session memory.

Due dependencies, shared_preload_libraries should to contains plpgsql first

postgres=# show shared_preload_libraries ;
┌──────────────────────────┐
│ shared_preload_libraries │
╞══════════════════════════╡
│ plpgsql,plpgsql_check    │
└──────────────────────────┘
(1 row)

The profiler is active when GUC plpgsql_check.profiler is on. The profiler doesn't require shared memory, but if there are not shared memory, then the profile is limmitted just to active session.

When plpgsql_check is initialized by shared_preload_libraries, another GUC is available to configure the amount of shared memory used by the profiler: plpgsql_check.profiler_max_shared_chunks. This defines the maximum number of statements chunk that can be stored in shared memory. For each plpgsql function (or procedure), the whole content is split into chunks of 30 statements. If needed, multiple chunks can be used to store the whole content of a single function. A single chunk is 1704 bytes. The default value for this GUC is 15000, which should be enough for big projects containing hundred of thousands of statements in plpgsql, and will consume about 24MB of memory. If your project doesn't require that much number of chunks, you can set this parameter to a smaller number in order to decrease the memory usage. The minimum value is 50 (which should consume about 83kB of memory), and the maximum value is 100000 (which should consume about 163MB of memory). Changing this parameter requires a PostgreSQL restart.

The profiler will also retrieve the query identifier for each instruction that contains an expression or optimizable statement. Note that this requires pg_stat_statements, or another similar third-party extension), to be installed. There are some limitations to the query identifier retrieval:

• if a plpgsql expression contains underlying statements, only the top level query identifier will be retrieved
• the profiler doesn't compute query identifier by itself but relies on external extension, such as pg_stat_statements, for that. It means that depending on the external extension behavior, you may not be able to see a query identifier for some statements. That's for instance the case with DDL statements, as pg_stat_statements doesn't expose the query identifier for such queries.
• a query identifier is retrieved only for instructions containing expressions. This means that plpgsql_profiler_function_tb() function can report less query identifier than instructions on a single line.

Attention: A update of shared profiles can decrease performance on servers under higher load.

The profile can be displayed by function plpgsql_profiler_function_tb:

postgres=# select lineno, avg_time, source from plpgsql_profiler_function_tb('fx(int)');
┌────────┬──────────┬───────────────────────────────────────────────────────────────────┐
│ lineno │ avg_time │                              source                               │
╞════════╪══════════╪═══════════════════════════════════════════════════════════════════╡
│      1 │          │                                                                   │
│      2 │          │ declare result int = 0;                                           │
│      3 │    0.075 │ begin                                                             │
│      4 │    0.202 │   for i in 1..$1 loop                                             │
│      5 │    0.005 │     select result + i into result; select result + i into result; │
│      6 │          │   end loop;                                                       │
│      7 │        0 │   return result;                                                  │
│      8 │          │ end;                                                              │
└────────┴──────────┴───────────────────────────────────────────────────────────────────┘
(9 rows)

The profile per statements (not per line) can be displayed by function plpgsql_profiler_function_statements_tb:

        CREATE OR REPLACE FUNCTION public.fx1(a integer)
         RETURNS integer
         LANGUAGE plpgsql
1       AS $function$
2       begin
3         if a > 10 then
4           raise notice 'ahoj';
5           return -1;
6         else
7           raise notice 'nazdar';
8           return 1;
9         end if;
10      end;
11      $function$

postgres=# select stmtid, parent_stmtid, parent_note, lineno, exec_stmts, stmtname
             from plpgsql_profiler_function_statements_tb('fx1');
┌────────┬───────────────┬─────────────┬────────┬────────────┬─────────────────┐
│ stmtid │ parent_stmtid │ parent_note │ lineno │ exec_stmts │    stmtname     │
╞════════╪═══════════════╪═════════════╪════════╪════════════╪═════════════════╡
│      0 │             ∅ │ ∅           │      2 │          0 │ statement block │
│      1 │             0 │ body        │      3 │          0 │ IF              │
│      2 │             1 │ then body   │      4 │          0 │ RAISE           │
│      3 │             1 │ then body   │      5 │          0 │ RETURN          │
│      4 │             1 │ else body   │      7 │          0 │ RAISE           │
│      5 │             1 │ else body   │      8 │          0 │ RETURN          │
└────────┴───────────────┴─────────────┴────────┴────────────┴─────────────────┘
(6 rows)

All stored profiles can be displayed by calling function plpgsql_profiler_functions_all:

postgres=# select * from plpgsql_profiler_functions_all();
┌───────────────────────┬────────────┬────────────┬──────────┬─────────────┬──────────┬──────────┐
│        funcoid        │ exec_count │ total_time │ avg_time │ stddev_time │ min_time │ max_time │
╞═══════════════════════╪════════════╪════════════╪══════════╪═════════════╪══════════╪══════════╡
│ fxx(double precision) │          1 │       0.01 │     0.01 │        0.00 │     0.01 │     0.01 │
└───────────────────────┴────────────┴────────────┴──────────┴─────────────┴──────────┴──────────┘
(1 row)

There are two functions for cleaning stored profiles: plpgsql_profiler_reset_all() and plpgsql_profiler_reset(regprocedure).

Coverage metrics

plpgsql_check provides two functions:

• plpgsql_coverage_statements(name)
• plpgsql_coverage_branches(name)

Note

There is another very good PLpgSQL profiler - https://bitbucket.org/openscg/plprofiler

My extension is designed to be simple for use and practical. Nothing more or less.

plprofiler is more complex. It build call graphs and from this graph it can creates flame graph of execution times.

Both extensions can be used together with buildin PostgreSQL's feature - tracking functions.

set track_functions to 'pl';
...
select * from pg_stat_user_functions;

Tracer

plpgsql_check provides a tracing possibility - in this mode you can see notices on start or end functions (terse and default verbosity) and start or end statements (verbose verbosity). For default and verbose verbosity the content of function arguments is displayed. The content of related variables are displayed when verbosity is verbose.

postgres=# do $$ begin perform fx(10,null, 'now', e'stěhule'); end; $$;
NOTICE:  #0 ->> start of inline_code_block (Oid=0)
NOTICE:  #2   ->> start of function fx(integer,integer,date,text) (Oid=16405)
NOTICE:  #2        call by inline_code_block line 1 at PERFORM
NOTICE:  #2       "a" => '10', "b" => null, "c" => '2020-08-03', "d" => 'stěhule'
NOTICE:  #4     ->> start of function fx(integer) (Oid=16404)
NOTICE:  #4          call by fx(integer,integer,date,text) line 1 at PERFORM
NOTICE:  #4         "a" => '10'
NOTICE:  #4     <<- end of function fx (elapsed time=0.098 ms)
NOTICE:  #2   <<- end of function fx (elapsed time=0.399 ms)
NOTICE:  #0 <<- end of block (elapsed time=0.754 ms)

The number after # is a execution frame counter (this number is related to deep of error context stack). It allows to pair start end and of function.

Tracing is enabled by setting plpgsql_check.tracer to on. Attention - enabling this behaviour has significant negative impact on performance (unlike the profiler). You can set a level for output used by tracer plpgsql_check.tracer_errlevel (default is notice). The output content is limited by length specified by plpgsql_check.tracer_variable_max_length configuration variable.

In terse verbose mode the output is reduced:

postgres=# set plpgsql_check.tracer_verbosity TO terse;
SET
postgres=# do $$ begin perform fx(10,null, 'now', e'stěhule'); end; $$;
NOTICE:  #0 start of inline code block (oid=0)
NOTICE:  #2 start of fx (oid=16405)
NOTICE:  #4 start of fx (oid=16404)
NOTICE:  #4 end of fx
NOTICE:  #2 end of fx
NOTICE:  #0 end of inline code block

In verbose mode the output is extended about statement details:

postgres=# do $$ begin perform fx(10,null, 'now', e'stěhule'); end; $$;
NOTICE:  #0            ->> start of block inline_code_block (oid=0)
NOTICE:  #0.1       1  --> start of PERFORM
NOTICE:  #2              ->> start of function fx(integer,integer,date,text) (oid=16405)
NOTICE:  #2                   call by inline_code_block line 1 at PERFORM
NOTICE:  #2                  "a" => '10', "b" => null, "c" => '2020-08-04', "d" => 'stěhule'
NOTICE:  #2.1       1    --> start of PERFORM
NOTICE:  #2.1                "a" => '10'
NOTICE:  #4                ->> start of function fx(integer) (oid=16404)
NOTICE:  #4                     call by fx(integer,integer,date,text) line 1 at PERFORM
NOTICE:  #4                    "a" => '10'
NOTICE:  #4.1       6      --> start of assignment
NOTICE:  #4.1                  "a" => '10', "b" => '20'
NOTICE:  #4.1              <-- end of assignment (elapsed time=0.076 ms)
NOTICE:  #4.1                  "res" => '130'
NOTICE:  #4.2       7      --> start of RETURN
NOTICE:  #4.2                  "res" => '130'
NOTICE:  #4.2              <-- end of RETURN (elapsed time=0.054 ms)
NOTICE:  #4                <<- end of function fx (elapsed time=0.373 ms)
NOTICE:  #2.1            <-- end of PERFORM (elapsed time=0.589 ms)
NOTICE:  #2              <<- end of function fx (elapsed time=0.727 ms)
NOTICE:  #0.1          <-- end of PERFORM (elapsed time=1.147 ms)
NOTICE:  #0            <<- end of block (elapsed time=1.286 ms)

Special feature of tracer is tracing of ASSERT statement when plpgsql_check.trace_assert is on. When plpgsql_check.trace_assert_verbosity is DEFAULT, then all function's or procedure's variables are displayed when assert expression is false. When this configuration is VERBOSE then all variables from all plpgsql frames are displayed. This behaviour is independent on plpgsql.check_asserts value. It can be used, although the assertions are disabled in plpgsql runtime.

postgres=# set plpgsql_check.tracer to off;
postgres=# set plpgsql_check.trace_assert_verbosity TO verbose;

postgres=# do $$ begin perform fx(10,null, 'now', e'stěhule'); end; $$;
NOTICE:  #4 PLpgSQL assert expression (false) on line 12 of fx(integer) is false
NOTICE:   "a" => '10', "res" => null, "b" => '20'
NOTICE:  #2 PL/pgSQL function fx(integer,integer,date,text) line 1 at PERFORM
NOTICE:   "a" => '10', "b" => null, "c" => '2020-08-05', "d" => 'stěhule'
NOTICE:  #0 PL/pgSQL function inline_code_block line 1 at PERFORM
ERROR:  assertion failed
CONTEXT:  PL/pgSQL function fx(integer) line 12 at ASSERT
SQL statement "SELECT fx(a)"
PL/pgSQL function fx(integer,integer,date,text) line 1 at PERFORM
SQL statement "SELECT fx(10,null, 'now', e'stěhule')"
PL/pgSQL function inline_code_block line 1 at PERFORM

postgres=# set plpgsql.check_asserts to off;
SET
postgres=# do $$ begin perform fx(10,null, 'now', e'stěhule'); end; $$;
NOTICE:  #4 PLpgSQL assert expression (false) on line 12 of fx(integer) is false
NOTICE:   "a" => '10', "res" => null, "b" => '20'
NOTICE:  #2 PL/pgSQL function fx(integer,integer,date,text) line 1 at PERFORM
NOTICE:   "a" => '10', "b" => null, "c" => '2020-08-05', "d" => 'stěhule'
NOTICE:  #0 PL/pgSQL function inline_code_block line 1 at PERFORM
DO

Attention - SECURITY

Tracer prints content of variables or function arguments. For security definer function, this content can hold security sensitive data. This is reason why tracer is disabled by default and should be enabled only with super user rights plpgsql_check.enable_tracer.

Pragma

You can configure plpgsql_check behave inside checked function with "pragma" function. This is a analogy of PL/SQL or ADA language of PRAGMA feature. PLpgSQL doesn't support PRAGMA, but plpgsql_check detects function named plpgsql_check_pragma and get options from parameters of this function. These plpgsql_check options are valid to end of group of statements.

CREATE OR REPLACE FUNCTION test()
RETURNS void AS $$
BEGIN
  ...
  -- for following statements disable check
  PERFORM plpgsql_check_pragma('disable:check');
  ...
  -- enable check again
  PERFORM plpgsql_check_pragma('enable:check');
  ...
END;
$$ LANGUAGE plpgsql;

The function plpgsql_check_pragma is immutable function that returns one. It is defined by plpgsql_check extension. You can declare alternative plpgsql_check_pragma function like:

CREATE OR REPLACE FUNCTION plpgsql_check_pragma(VARIADIC args[])
RETURNS int AS $$
SELECT 1
$$ LANGUAGE sql IMMUTABLE;

Using pragma function in declaration part of top block sets options on function level too.

CREATE OR REPLACE FUNCTION test()
RETURNS void AS $$
DECLARE
  aux int := plpgsql_check_pragma('disable:extra_warnings');
  ...

Shorter syntax for pragma is supported too:

CREATE OR REPLACE FUNCTION test()
RETURNS void AS $$
DECLARE r record;
BEGIN
  PERFORM 'PRAGMA:TYPE:r (a int, b int)';
  PERFORM 'PRAGMA:TABLE: x (like pg_class)';
  ...

Supported pragmas

echo:str - print string (for testing)

status:check,status:tracer, status:other_warnings, status:performance_warnings, status:extra_warnings,status:security_warnings

enable:check,enable:tracer, enable:other_warnings, enable:performance_warnings, enable:extra_warnings,enable:security_warnings

disable:check,disable:tracer, disable:other_warnings, disable:performance_warnings, disable:extra_warnings,disable:security_warnings

type:varname typename or type:varname (fieldname type, ...) - set type to variable of record type

table: name (column_name type, ...) or table: name (like tablename) - create ephereal table

Pragmas enable:tracer and disable:tracerare active for Postgres 12 and higher

Compilation

You need a development environment for PostgreSQL extensions:

make clean
make install

result:

[pavel@localhost plpgsql_check]$ make USE_PGXS=1 clean
rm -f plpgsql_check.so   libplpgsql_check.a  libplpgsql_check.pc
rm -f plpgsql_check.o
rm -rf results/ regression.diffs regression.out tmp_check/ log/
[pavel@localhost plpgsql_check]$ make USE_PGXS=1 all
clang -O2 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fpic -I/usr/local/pgsql/lib/pgxs/src/makefiles/../../src/pl/plpgsql/src -I. -I./ -I/usr/local/pgsql/include/server -I/usr/local/pgsql/include/internal -D_GNU_SOURCE   -c -o plpgsql_check.o plpgsql_check.c
clang -O2 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fpic -I/usr/local/pgsql/lib/pgxs/src/makefiles/../../src/pl/plpgsql/src -shared -o plpgsql_check.so plpgsql_check.o -L/usr/local/pgsql/lib -Wl,--as-needed -Wl,-rpath,'/usr/local/pgsql/lib',--enable-new-dtags  
[pavel@localhost plpgsql_check]$ su root
Password: *******
[root@localhost plpgsql_check]# make USE_PGXS=1 install
/usr/bin/mkdir -p '/usr/local/pgsql/lib'
/usr/bin/mkdir -p '/usr/local/pgsql/share/extension'
/usr/bin/mkdir -p '/usr/local/pgsql/share/extension'
/usr/bin/install -c -m 755  plpgsql_check.so '/usr/local/pgsql/lib/plpgsql_check.so'
/usr/bin/install -c -m 644 plpgsql_check.control '/usr/local/pgsql/share/extension/'
/usr/bin/install -c -m 644 plpgsql_check--0.9.sql '/usr/local/pgsql/share/extension/'
[root@localhost plpgsql_check]# exit
[pavel@localhost plpgsql_check]$ make USE_PGXS=1 installcheck
/usr/local/pgsql/lib/pgxs/src/makefiles/../../src/test/regress/pg_regress --inputdir=./ --psqldir='/usr/local/pgsql/bin'    --dbname=pl_regression --load-language=plpgsql --dbname=contrib_regression plpgsql_check_passive plpgsql_check_active plpgsql_check_active-9.5
(using postmaster on Unix socket, default port)
============== dropping database "contrib_regression" ==============
DROP DATABASE
============== creating database "contrib_regression" ==============
CREATE DATABASE
ALTER DATABASE
============== installing plpgsql                     ==============
CREATE LANGUAGE
============== running regression test queries        ==============
test plpgsql_check_passive    ... ok
test plpgsql_check_active     ... ok
test plpgsql_check_active-9.5 ... ok

=====================
 All 3 tests passed. 
=====================

Compilation on Ubuntu

Sometimes successful compilation can require libicu-dev package (PostgreSQL 10 and higher - when pg was compiled with ICU support)

sudo apt install libicu-dev

Compilation plpgsql_check on Windows

You can check precompiled dll libraries http://okbob.blogspot.cz/2015/02/plpgsqlcheck-is-available-for-microsoft.html

or compile by self:

1. Download and install PostgreSQL for Win32 from http://www.enterprisedb.com
2. Download and install Microsoft Visual C++ Express
3. Lern tutorial http://blog.2ndquadrant.com/compiling-postgresql-extensions-visual-studio-windows
4. Build plpgsql_check.dll
5. Install plugin
6. copy plpgsql_check.dll to PostgreSQL\14\lib
7. copy plpgsql_check.control and plpgsql_check--2.1.sql to PostgreSQL\14\share\extension

Checked on

• gcc on Linux (against all supported PostgreSQL)
• clang 3.4 on Linux (against PostgreSQL 10)
• for success regress tests the PostgreSQL 10 or higher is required

Compilation against PostgreSQL 10 requires libICU!

Licence

Copyright (c) Pavel Stehule (pavel.stehule@gmail.com)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Note

If you like it, send a postcard to address

Pavel Stehule
Skalice 12
256 01 Benesov u Prahy
Czech Republic

I invite any questions, comments, bug reports, patches on mail address pavel.stehule@gmail.com

---

Author: okbob
Source Code: https://github.com/okbob/plpgsql_check
License: View license

#postgresql 

Google's Flutter 1.20 stable announced with new features - Navoki

Flutter Google cross-platform UI framework has released a new version 1.20 stable.

Flutter is Google’s UI framework to make apps for Android, iOS, Web, Windows, Mac, Linux, and Fuchsia OS. Since the last 2 years, the flutter Framework has already achieved popularity among mobile developers to develop Android and iOS apps. In the last few releases, Flutter also added the support of making web applications and desktop applications.

Last month they introduced the support of the Linux desktop app that can be distributed through Canonical Snap Store(Snapcraft), this enables the developers to publish there Linux desktop app for their users and publish on Snap Store.  If you want to learn how to Publish Flutter Desktop app in Snap Store that here is the tutorial.

Flutter 1.20 Framework is built on Google’s made Dart programming language that is a cross-platform language providing native performance, new UI widgets, and other more features for the developer usage.

Here are the few key points of this release:

Performance improvements for Flutter and Dart

In this release, they have got multiple performance improvements in the Dart language itself. A new improvement is to reduce the app size in the release versions of the app. Another performance improvement is to reduce junk in the display of app animation by using the warm-up phase.

If your app is junk information during the first run then the Skia Shading Language shader provides for pre-compilation as part of your app’s build. This can speed it up by more than 2x.

Added a better support of mouse cursors for web and desktop flutter app,. Now many widgets will show cursor on top of them or you can specify the type of supported cursor you want.

Autofill for mobile text fields

Autofill was already supported in native applications now its been added to the Flutter SDK. Now prefilled information stored by your OS can be used for autofill in the application. This feature will be available soon on the flutter web.

A new widget for interaction

InteractiveViewer is a new widget design for common interactions in your app like pan, zoom drag and drop for resizing the widget. Informations on this you can check more on this API documentation where you can try this widget on the DartPad. In this release, drag-drop has more features added like you can know precisely where the drop happened and get the position.

Updated Material Slider, RangeSlider, TimePicker, and DatePicker

In this new release, there are many pre-existing widgets that were updated to match the latest material guidelines, these updates include better interaction with Slider and RangeSlider, DatePicker with support for date range and time picker with the new style.

New pubspec.yaml format

Other than these widget updates there is some update within the project also like in pubspec.yaml file format. If you are a flutter plugin publisher then your old pubspec.yaml  is no longer supported to publish a plugin as the older format does not specify for which platform plugin you are making. All existing plugin will continue to work with flutter apps but you should make a plugin update as soon as possible.

Preview of embedded Dart DevTools in Visual Studio Code

Visual Studio code flutter extension got an update in this release. You get a preview of new features where you can analyze that Dev tools in your coding workspace. Enable this feature in your vs code by _dart.previewEmbeddedDevTools_setting. Dart DevTools menu you can choose your favorite page embed on your code workspace.

Network tracking

The updated the Dev tools comes with the network page that enables network profiling. You can track the timings and other information like status and content type of your** network calls** within your app. You can also monitor gRPC traffic.

Generate type-safe platform channels for platform interop

Pigeon is a command-line tool that will generate types of safe platform channels without adding additional dependencies. With this instead of manually matching method strings on platform channel and serializing arguments, you can invoke native class and pass nonprimitive data objects by directly calling the Dartmethod.

There is still a long list of updates in the new version of Flutter 1.2 that we cannot cover in this blog. You can get more details you can visit the official site to know more. Also, you can subscribe to the Navoki newsletter to get updates on these features and upcoming new updates and lessons. In upcoming new versions, we might see more new features and improvements.

You can get more free Flutter tutorials you can follow these courses:

• Setup Flutter Desktop on Windows, Linux, MacOS using VSCode and Build – Flutter Tutorial
• Flutter Desktop Linux app | Build and Publish on Snapcraft Store
• Firebase Local Emulator Suite in Flutter

#dart #developers #flutter #app developed #dart devtools in visual studio code #firebase local emulator suite in flutter #flutter autofill #flutter date picker #flutter desktop linux app build and publish on snapcraft store #flutter pigeon #flutter range slider #flutter slider #flutter time picker #flutter tutorial #flutter widget #google flutter #linux #navoki #pubspec format #setup flutter desktop on windows

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