Flutter: ValueListenableBuilder 內容與ValueListenable保持"同步"的窗口小部件

• API

使用這個修改狀態可以不用setState()。

class _MyHomeState extends State<MyHome> {

  final ValueNotifier<int> _counter = ValueNotifier<int>(0);
  final Widget goodJob = const Text('Good job!');

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter Demo'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            ValueListenableBuilder(
              builder: (BuildContext context, int value, Widget child) {
                return Row(
                  mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                  children: <Widget>[
                    child,
                    Text('$value'),
                    child,
                  ],
                );
              },
              valueListenable: _counter,
              child: goodJob,
            )
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.plus_one),
        onPressed: () => _counter.value += 1,
      ),
    );
  }
}