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Bloc Fun
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| import 'dart:async'; | |
| import 'dart:math'; | |
| import 'package:flutter/foundation.dart'; | |
| import 'package:flutter/material.dart'; | |
| void main() => runApp(ExampleApp()); | |
| class ExampleApp extends StatefulWidget { | |
| @override | |
| ExampleAppState createState() => ExampleAppState(); | |
| } | |
| class ExampleAppState extends State<ExampleApp> { | |
| List<DataBloc> _blocs; | |
| @override | |
| void initState() { | |
| super.initState(); | |
| _blocs = List.generate(4, (int index) => DataBloc(index, 42)); | |
| } | |
| @override | |
| Widget build(BuildContext context) { | |
| return MaterialApp( | |
| debugShowCheckedModeBanner: false, | |
| theme: ThemeData.dark(), | |
| home: PageView.builder( | |
| itemCount: _blocs.length, | |
| itemBuilder: (BuildContext context, int index) { | |
| return BlocProvider<DataBloc>( | |
| creator: () => _blocs[index], | |
| child: ExampleScreen(), | |
| ); | |
| }, | |
| ), | |
| ); | |
| } | |
| } | |
| class ExampleScreen extends StatelessWidget { | |
| @override | |
| Widget build(BuildContext context) { | |
| final bloc = BlocProvider.of<DataBloc>(context); | |
| return Material( | |
| child: Column( | |
| children: <Widget>[ | |
| Expanded( | |
| child: Center( | |
| child: StreamBuilder<int>( | |
| stream: bloc.values, | |
| builder: (BuildContext context, AsyncSnapshot<int> snapshot) { | |
| final value = | |
| snapshot.hasData ? snapshot.data.toString() : ''; | |
| return AnimatedSwitcher( | |
| duration: const Duration(milliseconds: 250), | |
| child: Text( | |
| value, | |
| key: Key(value), | |
| textScaleFactor: 12.0, | |
| ), | |
| ); | |
| }, | |
| ), | |
| ), | |
| ), | |
| Container( | |
| alignment: Alignment.center, | |
| padding: const EdgeInsets.all(24.0), | |
| child: RaisedButton( | |
| color: Colors.pink, | |
| textColor: Colors.white, | |
| onPressed: bloc.nextValueAction, | |
| child: Text('Next'), | |
| ), | |
| ), | |
| ], | |
| ), | |
| ); | |
| } | |
| } | |
| class DataBloc extends Bloc { | |
| final Random _random = Random(); | |
| final int _index; | |
| final BehaviorSubject<int> _subject; | |
| DataBloc(this._index, int initialValue) | |
| : _subject = BehaviorSubject(initialValue); | |
| @override | |
| void init() => print(' init $_index: ${_subject.value}'); | |
| @override | |
| void dispose() => print('dispose $_index: ${_subject.value}'); | |
| Stream<int> get values => _subject.stream; | |
| void nextValueAction() { | |
| _subject.value = _random.nextInt(99); | |
| print(' value $_index: ${_subject.value}'); | |
| } | |
| } | |
| class BehaviorSubject<T> extends ValueListenable<T> { | |
| ValueNotifier<T> _latest; | |
| StreamController<T> _controller; | |
| BehaviorSubject(T value) { | |
| _latest = ValueNotifier<T>(value); | |
| _controller = StreamController<T>.broadcast( | |
| onListen: () => _controller.add(_latest.value), | |
| ); | |
| } | |
| Stream<T> get stream => _controller.stream; | |
| @override | |
| T get value => _latest.value; | |
| set value(T newValue) { | |
| if (_latest.value == newValue) return; | |
| _latest.value = newValue; | |
| _controller.add(newValue); | |
| } | |
| @override | |
| void addListener(listener) => _latest.addListener(listener); | |
| @override | |
| void removeListener(listener) => _latest.removeListener(listener); | |
| } | |
| abstract class Bloc { | |
| void init(); | |
| void dispose(); | |
| } | |
| // --- Warning: HERE BE TYPE DRAGONS! | |
| typedef BlocCreator<T extends Bloc> = T Function(); | |
| class BlocProvider<T extends Bloc> extends StatefulWidget { | |
| const BlocProvider({ | |
| Key key, | |
| @required this.creator, | |
| @required this.child, | |
| }) : super(key: key); | |
| final BlocCreator creator; | |
| final Widget child; | |
| @override | |
| _BlocProviderState createState() => _BlocProviderState<T>(); | |
| static T of<T extends Bloc>(BuildContext context) { | |
| final type = _typeOf<_BlocProviderScope<T>>(); | |
| final element = context.ancestorInheritedElementForWidgetOfExactType(type); | |
| return (element?.widget as _BlocProviderScope<T>)?.bloc; | |
| } | |
| static Type _typeOf<T>() => T; | |
| } | |
| class _BlocProviderState<T extends Bloc> extends State<BlocProvider<T>> { | |
| T _bloc; | |
| @override | |
| void initState() { | |
| super.initState(); | |
| _bloc = widget.creator(); | |
| _bloc.init(); | |
| } | |
| @override | |
| void dispose() { | |
| _bloc.dispose(); | |
| super.dispose(); | |
| } | |
| @override | |
| Widget build(BuildContext context) { | |
| return _BlocProviderScope( | |
| bloc: _bloc, | |
| child: widget.child, | |
| ); | |
| } | |
| } | |
| class _BlocProviderScope<T extends Bloc> extends InheritedWidget { | |
| const _BlocProviderScope({ | |
| Key key, | |
| @required this.bloc, | |
| @required Widget child, | |
| }) : super(key: key, child: child); | |
| final T bloc; | |
| @override | |
| bool updateShouldNotify(_BlocProviderScope oldWidget) => | |
| bloc != oldWidget.bloc; | |
| } |
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