什么是状态管理？

1class _MyHomePageState extends State<MyHomePage> {
2  int _counter = 0;
3
4  void _incrementCounter() {
5    setState(() {
6      _counter++;
7    });
8  }
9
10  @override
11  Widget build(BuildContext context) {
12    return Scaffold(
13      appBar: AppBar(
14        title: Text(widget.title),
15      ),
16      body: Center(
17        child: Column(
18          mainAxisAlignment: MainAxisAlignment.center,
19          children: <Widget>[
20            const Text(
21              'You have pushed the button this many times:',
22            ),
23            Text(
24              '$_counter',
25              style: Theme.of(context).textTheme.headline4,
26            ),
27          ],
28        ),
29      ),
30      floatingActionButton: FloatingActionButton(
31        onPressed: _incrementCounter,
32        tooltip: 'Increment',
33        child: const Icon(Icons.add),
34      ),
35    );
36  }
37}