如何从 Flutter 中的其他 StatefulWidget 设置/更新 StatefulWidget 的状态? [英] How to Set/Update State of StatefulWidget from other StatefulWidget in Flutter?
本文介绍了如何从 Flutter 中的其他 StatefulWidget 设置/更新 StatefulWidget 的状态?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
- 例如在下面的代码中,加号按钮起作用并且能够更新文本但减号按钮没有.
- 但是如果我们按下 FloatingActionButton 则状态会刷新.
- 减号按钮正在改变变量的值,但不是更新父小部件的状态.
这里是代码.....
import 'package:flutter/material.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
int number;
EdgeInsets globalMargin = const EdgeInsets.symmetric(horizontal: 20.0, vertical: 20.0);
TextStyle textStyle = const TextStyle(
fontSize: 100.0,
color: Colors.black,
);
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
@override
void initState() {
super.initState();
number = number ?? 0;
}
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text(widget.title),
),
body: new Column(
children: <Widget>[
new Text(
number.toString(),
style: textStyle,
),
new GridView.count(
crossAxisCount: 2,
shrinkWrap: true,
scrollDirection: Axis.vertical,
children: <Widget>[
new InkResponse(
child: new Container(
margin: globalMargin,
color: Colors.green,
child: new Center(
child: new Text(
"+",
style: textStyle,
),
)),
onTap: () {
setState(() {
number = number + 1;
});
},
),
new Sub(),
],
),
],
),
floatingActionButton: new FloatingActionButton(
onPressed: () {
setState(() {});
},
child: new Icon(Icons.update),
),
);
}
}
class Sub extends StatefulWidget {
@override
_SubState createState() => new _SubState();
}
class _SubState extends State<Sub> {
@override
Widget build(BuildContext context) {
return new InkResponse(
child: new Container(
margin: globalMargin,
color: Colors.red,
child: new Center(
child: new Text(
"-",
style: textStyle,
),
)),
onTap: () {
setState(() {
number = number - 1;
});
},
);
}
}
推荐答案
旧解决方案:
- 创建_MyHomePageState 的全局实例.在 _SubState 中使用此实例作为 _myHomePageState.setState
- 无需创建全局实例.相反,只需将父实例传递给子小部件
新解决方案:通过回调似乎比上述解决方案更好
New Solution: Passing a callback seems the better solution than above solutions
根据 FLUTTER 2.0 更新代码:
import 'package:flutter/material.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new MyHomePage(),
);
}
}
EdgeInsets globalMargin =
const EdgeInsets.symmetric(horizontal: 20.0, vertical: 20.0);
TextStyle textStyle = const TextStyle(
fontSize: 100.0,
color: Colors.black,
);
class MyHomePage extends StatefulWidget {
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int number = 0;
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text('SO Help'),
),
body: new Column(
children: <Widget>[
new Text(
number.toString(),
style: textStyle,
),
new GridView.count(
crossAxisCount: 2,
shrinkWrap: true,
scrollDirection: Axis.vertical,
children: <Widget>[
new InkResponse(
child: new Container(
margin: globalMargin,
color: Colors.green,
child: new Center(
child: new Text(
"+",
style: textStyle,
),
)),
onTap: () {
setState(() {
this.number++;
});
},
),
new Sub(onTap: () {
setState(() {
this.number--;
});
}),
],
),
],
),
floatingActionButton: new FloatingActionButton(
onPressed: () {
setState(() {});
},
child: new Icon(Icons.update),
),
);
}
}
class Sub extends StatelessWidget {
final Function onTap;
Sub({this.onTap});
@override
Widget build(BuildContext context) {
return new InkResponse(
child: new Container(
margin: globalMargin,
color: Colors.red,
child: new Center(
child: new Text(
"-",
style: textStyle,
),
),
),
onTap: this.onTap,
);
}
}
告诉我它是否有效.
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