【自学Flutter】25 InheritedWidget数据共享的使用

import 'package:flutter/material.dart';
 
void main() => runApp(MyApp());
 
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}
 
class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}
 
class _MyHomePageState extends State<MyHomePage> {
  int counter = 0;
 
  void _incrementCounter() {
    setState(() {
      counter++;
    });
  }
 
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter Demo'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            CounterText(), // 使用 CounterText Widget
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}
 
class CounterText extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // 使用 InheritedWidget 中的共享数据
    return Text(
      '${context.dependOnInheritedWidgetOfExactType<CounterInheritedWidget>().data}',
      style: Theme.of(context).textTheme.headline4,
    );
  }
}
 
class CounterInheritedWidget extends InheritedWidget {
  final int data;
 
  CounterInheritedWidget({
    Key key,
    @required this.data,
    @required Widget child,
  }) : super(key: key, child: child);
 
  // 确定是否需要重新构建 Widget
  @override
  bool updateShouldNotify(CounterInheritedWidget oldWidget) => data != oldWidget.data;
}

在这个代码示例中，我们创建了一个CounterInheritedWidget类，它继承自InheritedWidget并包含一个整数数据。在_MyHomePageState的build方法中，我们使用CounterInheritedWidget来包裹需要共享数据的子Widget。CounterText Widget通过dependOnInheritedWidgetOfExactType方法获取共享的数据并显示。这样，我们就可以在不同的Widget树层级间共享数据，而不需要通过构造函数或者任何回调函数来传递数据。