Dart语言及Flutter项目

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// 延迟2秒后返回结果
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Future.delayed(Duration(seconds: 2),(){
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   return "hi world!";
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}).then((data){
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   print(data);
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});
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// 抛出异常
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Future.delayed(Duration(seconds: 2),(){
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   //return "hi world!";
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   throw AssertionError("Error");
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}).then((data){
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   //执行成功会走到这里
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   print("success");
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}).catchError((e){
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   //执行失败会走到这里
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   print(e);
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}).whenComplete((){
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   //无论成功或失败都会走到这里
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});
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// 执行多个异步
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Future.wait([
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  // 2秒后返回结果
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  Future.delayed(Duration(seconds: 2), () {
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    return "hello";
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  }),
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  // 4秒后返回结果
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  Future.delayed(Duration(seconds: 4), () {
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    return " world";
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  })
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]).then((results){
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  print(results[0]+results[1]);
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}).catchError((e){
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  print(e);
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});

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Stream.fromFutures([
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  // 1秒后返回结果
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  Future.delayed(Duration(seconds: 1), () {
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    return "hello 1";
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  }),
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  // 抛出一个异常
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  Future.delayed(Duration(seconds: 2),(){
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    throw AssertionError("Error");
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  }),
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  // 3秒后返回结果
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  Future.delayed(Duration(seconds: 3), () {
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    return "hello 3";
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  })
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]).listen((data){
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   print(data);
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}, onError: (e){
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   print(e.message);
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},onDone: (){
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});

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class _MyHomePageState extends State<MyHomePage> {
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  int _counter = 0;
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  void _incrementCounter() {
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    setState(() {
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      _counter++;
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    });
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  }
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  @override
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  Widget build(BuildContext context) {
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    return Scaffold(
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      appBar: AppBar(
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        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
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        title: Text(widget.title),
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      ),
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      body: Center(
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        child: Column(
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          mainAxisAlignment: MainAxisAlignment.center,
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          children: <Widget>[
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            const Text(
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              'You have pushed the button this many times:',
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            ),
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            Text(
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              '$_counter',
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              style: Theme.of(context).textTheme.headlineMedium,
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            ),
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          ],
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        ),
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      ),
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      floatingActionButton: FloatingActionButton(
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        onPressed: _incrementCounter,
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        tooltip: 'Increment',
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        child: const Icon(Icons.add),
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      ), // This trailing comma makes auto-formatting nicer for build methods.
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    );
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  }
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}

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import 'package:flutter/material.dart';
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void main() {
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  runApp(const MyApp());
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}
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class MyApp extends StatelessWidget {
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  const MyApp({super.key});
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  // 这个部件是应用程序的根
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  @override
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  Widget build(BuildContext context) {
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    return MaterialApp(
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      title: 'Flutter Demo',
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      theme: ThemeData(
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        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
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        useMaterial3: true,
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      ),
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      home: const StateLifeCycleTest(),
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    );
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  }
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}
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class StateLifeCycleTest extends StatelessWidget {
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  const StateLifeCycleTest({Key? key}) : super(key: key);
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  @override
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  Widget build(BuildContext context) {
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    return CounterWidget();
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  }
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}
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class CounterWidget extends StatefulWidget {
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  const CounterWidget({super.key, this.initValue = 0});
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  final int initValue;
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  @override
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  _CounterWidgetState createState() => _CounterWidgetState();
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}
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class _CounterWidgetState extends State<CounterWidget> {
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  int _counter = 0;
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  @override
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  void initState() {
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    super.initState();
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    // 初始化状态
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    _counter = widget.initValue;
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    print('initState');
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  }
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  @override
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  Widget build(BuildContext context) {
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    print('build');
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    return Scaffold(
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        body: Center(
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            child: TextButton(
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                child: Text('$_counter'),
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                onPressed: () => setState(
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                      () => ++_counter,
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                    ))));
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  }
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  @override
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  void didUpdateWidget(CounterWidget oldWidget) {
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    super.didUpdateWidget(oldWidget);
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    print('didUpdateWidget');
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  }
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  @override
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  void deactivate() {
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    super.deactivate();
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    print('deactivate');
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  }
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  @override
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  void dispose() {
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    super.dispose();
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    print("dispose");
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  }
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  @override
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  void reassemble() {
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    super.reassemble();
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    print("reassemble");
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  }
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  @override
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  void didChangeDependencies() {
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    super.didChangeDependencies();
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    print("didChangeDependencies");
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  }
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}

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import 'package:flutter/material.dart';
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void main() => runApp(MyApp());
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class MyApp extends StatelessWidget {
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  @override
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  Widget build(BuildContext context) {
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    return MaterialApp(
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      home: Scaffold(
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        appBar: AppBar(
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          title: Text('父子通信'),
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        ),
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        body: MyWidget(),
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      ),
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    );
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  }
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}
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class MyWidget extends StatefulWidget {
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  @override
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  _MyWidgetState createState() => _MyWidgetState();
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}
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class _MyWidgetState extends State<MyWidget> {
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  int _counter = 0;
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  void incrementCounter() {
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    setState(() {
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      _counter++;
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    });
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  }
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  @override
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  Widget build(BuildContext context) {
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    return Column(
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      children: [
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        Center(
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          child: Text('Counter: $_counter'),
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        ),
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        ChildWidget(),
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      ],
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    );
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  }
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}
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class ChildWidget extends StatelessWidget {
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  @override
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  Widget build(BuildContext context) {
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    // 通过BuildContext查找父级State对象
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    _MyWidgetState? parentState =
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        context.findAncestorStateOfType<_MyWidgetState>();
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    return ElevatedButton(
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      onPressed: () {
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        parentState?.incrementCounter();
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      },
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      child: Text('父节点数据：${parentState?._counter ?? 0}'),
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    );
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  }
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}