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class MyHomePage extends StatelessWidget {
  final number = new ValueNotifier(0);//值变化通知
 
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ValueListenableBuilder<int>(
        valueListenable: number,
        builder: (context, value, child) {
          return Center(
            child: RaisedButton(
              onPressed: () {
                number.value++;//触发通知
              },
              child: MyWidget(number),
            ),
          );
        },
      ),
    );
  }
}
 
class MyWidget extends StatelessWidget {
  final ValueListenable<int> number;
 
  MyWidget(this.number);
 
  @override
  Widget build(BuildContext context) {
    return new Text(number.value.toString());//同步变化
  }
}