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| import 'package:flutter/material.dart'; | |
| void main() { | |
| runApp(MyApp()); | |
| } | |
| class MyApp extends StatelessWidget { | |
| @override | |
| Widget build(BuildContext context) { | |
| return MaterialApp( | |
| title: 'Flutter Demo', | |
| theme: ThemeData( | |
| primarySwatch: Colors.blue, | |
| ), | |
| home: MyHomePage(title: 'Flutter Demo Home Page'), | |
| ); | |
| } | |
| } | |
| class MyHomePage extends StatefulWidget { | |
| MyHomePage({Key? key, required this.title}) : super(key: key); | |
| final String title; | |
| @override | |
| _MyHomePageState createState() => _MyHomePageState(); | |
| } | |
| class _MyHomePageState extends State<MyHomePage> { | |
| int _counter = 0; | |
| void _incrementCounter() { | |
| setState(() { | |
| _counter++; | |
| }); | |
| } | |
| @override | |
| Widget build(BuildContext context) { | |
| print('MyHomePage is rebuilt with $_counter'); | |
| return Scaffold( | |
| appBar: AppBar( | |
| title: Text(widget.title), | |
| ), | |
| body: Center( | |
| child: CountValue( | |
| value: _counter, | |
| child: Column( | |
| mainAxisAlignment: MainAxisAlignment.center, | |
| children: <Widget>[ | |
| const FixedTextWidget(), | |
| const DummyInBetweenWidget(), | |
| ], | |
| ), | |
| ), | |
| ), | |
| floatingActionButton: FloatingActionButton( | |
| onPressed: _incrementCounter, | |
| tooltip: 'Increment', | |
| child: Icon(Icons.add), | |
| ), | |
| ); | |
| } | |
| } | |
| class FixedTextWidget extends StatelessWidget { | |
| const FixedTextWidget({ | |
| Key? key, | |
| }) : super(key: key); | |
| @override | |
| Widget build(BuildContext context) { | |
| print('FixedText is rebuilt'); | |
| return Text( | |
| 'You have pushed the button this many times:', | |
| ); | |
| } | |
| } | |
| class CountDisplayWidget extends StatelessWidget { | |
| const CountDisplayWidget({ | |
| Key? key | |
| }) : super(key: key); | |
| @override | |
| Widget build(BuildContext context) { | |
| int counter = CountValue.of(context).value; | |
| print('CountDisplay is rebuilt with $counter'); | |
| return Text( | |
| '$counter', | |
| style: Theme.of(context).textTheme.headline4, | |
| ); | |
| } | |
| } | |
| class CountValue extends InheritedWidget { | |
| const CountValue({ | |
| Key? key, | |
| required this.value, | |
| required Widget child, | |
| }) : super(key: key, child: child); | |
| final int value; | |
| static CountValue of(BuildContext context) { | |
| final CountValue? result = context.dependOnInheritedWidgetOfExactType<CountValue>(); | |
| assert(result != null, 'No CountValue found in context'); | |
| return result!; | |
| } | |
| @override | |
| bool updateShouldNotify(CountValue old) => value != old.value; | |
| } | |
| class DummyInBetweenWidget extends StatelessWidget { | |
| const DummyInBetweenWidget({ | |
| Key? key, | |
| }) : super(key: key); | |
| @override | |
| Widget build(BuildContext context) { | |
| print('DummyInBetweenWidget is rebuilt'); | |
| return const CountDisplayWidget(); | |
| } | |
| } | |
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