Flutter 当父状态设置为颤振时,计时器未重置
这是一个简单的颤振小部件,显示倒计时:-Flutter 当父状态设置为颤振时,计时器未重置,flutter,timer,widget,state,Flutter,Timer,Widget,State,这是一个简单的颤振小部件,显示倒计时:- class MyWidget extends StatefulWidget { @override _MyWidgetState createState() => _MyWidgetState(); } class _MyWidgetState extends State<MyWidget> { @override Widget build(BuildContext context) { return Column(
class MyWidget extends StatefulWidget {
@override
_MyWidgetState createState() => _MyWidgetState();
}
class _MyWidgetState extends State<MyWidget> {
@override
Widget build(BuildContext context) {
return Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
MyTimer(
count: 25,
),
RaisedButton(
onPressed: () {
setState(() {});
},
)
],
);
}
}
class MyTimer extends StatefulWidget {
final int count;
MyTimer({this.count});
@override
_MyTimerState createState() => _MyTimerState(count: this.count);
}
class _MyTimerState extends State<MyTimer> {
final int count;
Timer _timer;
int _start;
_MyTimerState({this.count});
@override
void initState() {
_start = this.count;
const oneSec = const Duration(seconds: 1);
_timer = Timer.periodic(
oneSec,
(Timer timer) => setState(
() {
if (_start < 1) {
_timer.cancel();
} else {
_start = _start - 1;
}
},
),
);
}
@override
Widget build(BuildContext context) {
return Text(this._start.toString());
}
}
当我按下父级上的按钮时,将设置并重建父级,这将导致MyTimer小部件再次生成,从而将计时器再次重置为25
这就是我所想的,但按下按钮并在父对象上设置状态并不能重建MyTimer小部件?
这种行为的原因是什么
编辑:您可以在DartPad中使用颤振创建新的pad来尝试此代码。您可以复制下面的粘贴运行完整代码 因为initState只调用一次,所以可以在_MyTimerState中重写didUpdateWidget 代码片段
@override
void didUpdateWidget(MyTimer oldWidget) {
super.didUpdateWidget(oldWidget);
_start = widget.count;
}
工作演示
完整代码
import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart';
import 'dart:async';
class MyWidget extends StatefulWidget {
@override
_MyWidgetState createState() => _MyWidgetState();
}
class _MyWidgetState extends State<MyWidget> {
@override
Widget build(BuildContext context) {
return Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
MyTimer(
count: 25,
),
RaisedButton(
onPressed: () {
setState(() {});
},
)
],
);
}
}
class MyTimer extends StatefulWidget {
final int count;
MyTimer({this.count});
@override
_MyTimerState createState() => _MyTimerState(count: this.count);
}
class _MyTimerState extends State<MyTimer> {
final int count;
Timer _timer;
int _start;
_MyTimerState({this.count});
@override
void initState() {
print("initSate");
_start = this.count;
const oneSec = const Duration(seconds: 1);
_timer = Timer.periodic(
oneSec,
(Timer timer) => setState(
() {
if (_start < 1) {
_timer.cancel();
} else {
_start = _start - 1;
}
},
),
);
}
@override
void didUpdateWidget(MyTimer oldWidget) {
super.didUpdateWidget(oldWidget);
_start = widget.count;
}
@override
Widget build(BuildContext context) {
return Text(this._start.toString());
}
}
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
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>[
MyWidget(),
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),
),
);
}
}