是否可以从其他小部件 onPressed()
方法调用特定小部件(嵌入在其他小部件中)的 setState()
方法,所以只有 那个 小部件被重绘了?
我想点击按钮并查看“MyTextWidget”的状态发生变化。其余布局相同,没有任何变化,因此不应重写。
这是我的代码:
import 'package:flutter/material.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Timer',
theme: new ThemeData(
primaryColor: Colors.grey.shade800,
),
home: new MyHomePage(),
);
}
}
class MyHomePage extends StatelessWidget {
int _seconds = 1;
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("title"),
),
body: Column(
mainAxisAlignment: MainAxisAlignment.spaceAround,
children: <Widget>[
MyTextWidget(), //just update this widget
Divider(),
Row(
mainAxisAlignment: MainAxisAlignment.spaceAround,
children: <Widget>[
IconButton(
icon: Icon(Icons.add_circle),
onPressed: _addPressed,
iconSize: 150.0,
),
IconButton(
icon: Icon(Icons.remove_circle),
onPressed: ()=> print("to be implemented"),
iconSize: 150.0,
),
],
)
],
),
);
}
void _addPressed() {
//somehow call _updateSeconds()
}
}
这是我要更新的有状态的 MyTextWidget。
class MyTextWidget extends StatefulWidget{
@override
_MyTextWidgetState createState() => _MyTextWidgetState();
}
class _MyTextWidgetState extends State<MyTextWidget> {
int secondsToDisplay = 0;
void _updateSeconds(int newSeconds) {
setState(() {
secondsToDisplay = newSeconds;
});
}
@override
Widget build(BuildContext context) {
return Text(
secondsToDisplay.toString(),
textScaleFactor: 5.0,
);
}
}
我想要实现的目标似乎很简单,但我无法弄清楚。想象一下,如果“MyTextWidget”被埋在巨大的布局树中,每次我想更新它时,我都需要重新绘制整个树。
最佳答案
这是使用流的可能解决方案:
import 'dart:async';
import 'package:flutter/material.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Timer',
theme: new ThemeData(
primaryColor: Colors.grey.shade800,
),
home: new MyHomePage(),
);
}
}
class MyHomePage extends StatelessWidget {
StreamController<int> _controller = StreamController<int>();
int _seconds = 1;
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("title"),
),
body: Column(
mainAxisAlignment: MainAxisAlignment.spaceAround,
children: <Widget>[
MyTextWidget(stream: _controller.stream), //just update this widget
Divider(),
Row(
mainAxisAlignment: MainAxisAlignment.spaceAround,
children: <Widget>[
IconButton(
icon: Icon(Icons.add_circle),
onPressed: _addPressed,
iconSize: 150.0,
),
IconButton(
icon: Icon(Icons.remove_circle),
onPressed: ()=> _controller.add(_seconds++),
iconSize: 150.0,
),
],
)
],
),
);
}
void _addPressed() {
//somehow call _updateSeconds()
}
}
class MyTextWidget extends StatefulWidget{
final Stream<int> stream;
MyTextWidget({this.stream});
@override
_MyTextWidgetState createState() => _MyTextWidgetState();
}
class _MyTextWidgetState extends State<MyTextWidget> {
int secondsToDisplay = 0;
void _updateSeconds(int newSeconds) {
setState(() {
secondsToDisplay = newSeconds;
});
}
@override
void initState() {
super.initState();
widget.stream.listen((seconds) {
_updateSeconds(seconds);
});
}
@override
Widget build(BuildContext context) {
return Text(
secondsToDisplay.toString(),
textScaleFactor: 5.0,
);
}
}
关于dart - Flutter - 从其他小部件调用 setState(),我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/52761888/