Flutter:外部小部件的setState

Question

在默认的新flutter项目中，有floatingActionButton。我希望它在外部文件/小部件中，但在使用setState((时遇到问题

这可能吗？感谢

class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}

Answer 1

您可以将_incrementCounter方法传递给其他小部件。

文件1:

class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: IncrementCounterButton(
incrementCounter: _incrementCounter,
),
);
}
}

文件2:

class IncrementCounterButton extends StatelessWidget {
final void Function() incrementCounter;
IncrementCounterButton({Key key, this.incrementCounter) : super(key: key);
@override
Widget build(BuildContext context) {
return  FloatingActionButton(
onPressed: incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
);
}
}

Answer 2

你必须传递函数而不是调用它

onPressed: () { _incrementCounter(); },

或者像这样你们喜欢的快捷方式：

onPressed: () => _incrementCounter(),

希望它能有所帮助！快乐编码：(