Forked from rrousselGit/functions_vs_class_performance.dart
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| import 'package:flutter/material.dart'; | |
| // This example showcases how extracting widgets into StatelessWidgets | |
| // instead of functions can improve performances, by rebuilding | |
| // only what needs to update when the state changes | |
| void main() => runApp(MyApp()); | |
| class MyApp extends StatelessWidget { | |
| @override | |
| Widget build(context) { | |
| return Counter( | |
| count: Count(), | |
| child: MaterialApp( | |
| home: Home(), | |
| ), | |
| ); | |
| } | |
| } | |
| class Count extends ValueNotifier<int> { | |
| Count() : super(0); | |
| } | |
| class Counter extends InheritedNotifier { | |
| Counter({ | |
| Key key, | |
| this.count, | |
| Widget child, | |
| }) : super(key: key, child: child, notifier: count); | |
| final Count count; | |
| static Count of(BuildContext context, {bool listen = true}) { | |
| if (listen) { | |
| return context.dependOnInheritedWidgetOfExactType<Counter>().count; | |
| } else { | |
| final Counter counter = | |
| context.getElementForInheritedWidgetOfExactType<Counter>().widget; | |
| return counter.count; | |
| } | |
| } | |
| } | |
| class Home extends StatelessWidget { | |
| @override | |
| Widget build(BuildContext context) { | |
| print('Home build'); | |
| return Scaffold( | |
| body: Center( | |
| // By extracting Title in a StatelessWidget, Home doesn't rebuild when the counter changes | |
| child: Title(), | |
| // Uncommenting this code causes Home to rebuild when the counter changes | |
| // child: Text('Count ${Counter.of(context).value}') | |
| ), | |
| floatingActionButton: FloatingActionButton( | |
| onPressed: () => Counter.of(context, listen: false).value++, | |
| child: Icon(Icons.add), | |
| ), | |
| ); | |
| } | |
| } | |
| class Title extends StatelessWidget { | |
| Widget build(context) { | |
| print('build Title'); | |
| return Text('Count ${Counter.of(context).value}'); | |
| } | |
| } |
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