默认情况下,当StatefulWidget
上的状态发生变化时,状态转换时没有动画。有什么办法吃吗?例如,在过渡时,我要淡出旧状态并淡入新状态。
我知道如何在路线之间添加过渡动画,但是找不到在状态过渡之间进行过渡的方法。
有一个例子,让我们使用Flutter默认应用程序:
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@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>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}
因此,每次我单击按钮时,数字都会立即更改。我想看到的是旧数字逐渐消失,新数字逐渐消失。
答案 0 :(得分:1)
这取决于您如何管理它,它可以使用animationController并使用不透明度窗口小部件的值来工作,您需要添加Mixin with SingleTickerProviderStateMixin
才能使动画起作用。
这是您可以等待的等待时间之一,但是如果您只想要淡入淡出效果,则可以使用AnimatedOpacity。
像这样:
import 'dart:async';
import 'package:flutter/material.dart';
class HomePage extends StatefulWidget {
HomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
int _counter = 0;
double _opacity = 1;
void _incrementCounter() {
setState(() => _opacity = 0);
Future.delayed(Duration(milliseconds: 500),() =>
setState(() {
_counter++;
_opacity = 1;
}
));
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
AnimatedOpacity(
opacity: _opacity,
duration: Duration(milliseconds: 500),
child: Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}
这是一种进行fadeOur / FadeIn的简单方法,就像我说的那样,如果您需要完整的动画并对其进行更多控制,则绝对应该使用AnimationController。
答案 1 :(得分:0)
This answer,使用AnimatedOpacity
可以正常工作。但是我发现使用AnimatedSwitcher
更简单,更干净。
(...)
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
AnimatedSwitcher(
duration: const Duration(milliseconds: 500),
transitionBuilder: (Widget child, Animation<double> animation) {
return FadeTransition(child: child, opacity: animation);
},
child: Text(
'$_counter',
key: ValueKey<int>(_counter),
style: Theme.of(context).textTheme.display1,
),
),
],
),
),
(...)
有关AnimatedSwitcher
的更多信息,请参见here。