A Flutter Wrapper for A ScrollView That Will Trigger A Callback

Lazy load scrollview 

A wrapper for a ScrollView that will enable lazy loading

Usage 

Add lazy_load_scrollview dependency to your pubspec.yaml:

dependencies:
  lazy_load_scrollview: 1.3.0

In your Dart code, import package:lazy_load_scrollview/lazy_load_scrollview.dart Then you can wrap your ListView, GridView, RefreshIndicator etc with the LazyLoadScrollView. Make sure you add an endOfPageListener which will receive the call when the bottom of the list has been reached.

import 'package:lazy_load_scrollview/lazy_load_scrollview.dart';


@override
Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: LazyLoadScrollView(
        onEndOfPage: () => loadMore(),
        child: ListView.builder(
          itemCount: data.length,
          itemBuilder: (context, position) {
            return Text("Position $position");
          },
        ),
      ),
    );
}

Class definition 

LazyLoadScrollView(
  endOfPageListener: () => loadMore(), // The callback when reaching the end of the list
  scrollOffset: 100 // Pixels from the bottom that should trigger a callback 
  child: Widget, // A subclass of `ScrollView`
);

Use this package as a library

Depend on it

Run this command:

With Flutter:

 $ flutter pub add lazy_load_scrollview

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

dependencies:
  lazy_load_scrollview: ^1.3.0

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:lazy_load_scrollview/lazy_load_scrollview.dart';

example/lib/main.dart

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

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Lazy Load Demo',
      home: new MyHomePage(title: 'Lazy Load Demo'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  List<int> verticalData = [];
  List<int> horizontalData = [];

  final int increment = 10;

  bool isLoadingVertical = false;
  bool isLoadingHorizontal = false;

  @override
  void initState() {
    _loadMoreVertical();
    _loadMoreHorizontal();
    super.initState();
  }

  Future _loadMoreVertical() async {
    setState(() {
      isLoadingVertical = true;
    });

    // Add in an artificial delay
    await new Future.delayed(const Duration(seconds: 2));

    verticalData.addAll(
        List.generate(increment, (index) => verticalData.length + index));

    setState(() {
      isLoadingVertical = false;
    });
  }

  Future _loadMoreHorizontal() async {
    setState(() {
      isLoadingHorizontal = true;
    });

    // Add in an artificial delay
    await new Future.delayed(const Duration(seconds: 2));

    horizontalData.addAll(
        List.generate(increment, (index) => horizontalData.length + index));

    setState(() {
      isLoadingHorizontal = false;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: LazyLoadScrollView(
        isLoading: isLoadingVertical,
        onEndOfPage: () => _loadMoreVertical(),
        child: Scrollbar(
          child: ListView(
            children: [
              Padding(
                padding: const EdgeInsets.all(8.0),
                child: Text(
                  'Nested horizontal ListView',
                  textAlign: TextAlign.center,
                ),
              ),
              Container(
                  height: 180,
                  child: LazyLoadScrollView(
                      isLoading: isLoadingHorizontal,
                      scrollDirection: Axis.horizontal,
                      onEndOfPage: () => _loadMoreHorizontal(),
                      child: Scrollbar(
                          child: ListView.builder(
                              itemCount: horizontalData.length,
                              scrollDirection: Axis.horizontal,
                              itemBuilder: (context, position) {
                                return DemoItem(position);
                              })))),
              Padding(
                padding: const EdgeInsets.all(8.0),
                child: Text(
                  'Vertical ListView',
                  textAlign: TextAlign.center,
                ),
              ),
              ListView.builder(
                shrinkWrap: true,
                physics: NeverScrollableScrollPhysics(),
                itemCount: verticalData.length,
                itemBuilder: (context, position) {
                  return DemoItem(position);
                },
              ),
            ],
          ),
        ),
      ),
    );
  }
}

class DemoItem extends StatelessWidget {
  final int position;

  const DemoItem(
    this.position, {
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SizedBox(
      width: MediaQuery.of(context).size.width,
      child: Card(
        child: Padding(
          padding: const EdgeInsets.all(8.0),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              Row(
                crossAxisAlignment: CrossAxisAlignment.center,
                children: <Widget>[
                  Container(
                    color: Colors.grey,
                    height: 40.0,
                    width: 40.0,
                  ),
                  SizedBox(width: 8.0),
                  Text("Item $position"),
                ],
              ),
              Text(
                  "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Quisque sed vulputate orci. Proin id scelerisque velit. Fusce at ligula ligula. Donec fringilla sapien odio, et faucibus tortor finibus sed. Aenean rutrum ipsum in sagittis auctor. Pellentesque mattis luctus consequat. Sed eget sapien ut nibh rhoncus cursus. Donec eget nisl aliquam, ornare sapien sit amet, lacinia quam."),
            ],
          ),
        ),
      ),
    );
  }
}

Download details:

Author: quirijngb.com

Source: https://github.com/QuirijnGB/lazy-load-scrollview

#flutter #android #ios #web-development #dart