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@override |
State<SampleAppPage> createState() => _SampleAppPageState(); |
} |
class _SampleAppPageState extends State<SampleAppPage> { |
// default value for toggle. |
bool toggle = true; |
void _toggle() { |
setState(() { |
toggle = !toggle; |
}); |
} |
widget _getToggleChild() { |
if (toggle) { |
return const Text('Toggle one'); |
} else { |
return ElevatedButton( |
onPressed: () {}, |
child: const Text('Toggle two'), |
); |
} |
} |
@override |
widget build(BuildContext context) { |
return scaffold( |
appBar: AppBar( |
title: const Text('Sample app'), |
), |
body: center( |
child: _getToggleChild(), |
), |
floatingActionButton: FloatingActionButton( |
onPressed: _toggle, |
tooltip: 'update text', |
child: const Icon(Icons.update), |
), |
); |
} |
} |
<code_end> |
<topic_end> |
<topic_start> |
how do i animate a widget? |
in android, you either create animations using XML, or call the animate() |
method on a view. in flutter, animate widgets using the animation |
library by wrapping widgets inside an animated widget. |
in flutter, use an AnimationController which is an animation<double> |
that can pause, seek, stop and reverse the animation. it requires a ticker |
that signals when vsync happens, and produces a linear interpolation between |
0 and 1 on each frame while it’s running. you then create one or more |
animations and attach them to the controller. |
for example, you might use CurvedAnimation to implement an animation |
along an interpolated curve. in this sense, the controller |
is the “master” source of the animation progress and the CurvedAnimation |
computes the curve that replaces the controller’s default linear motion. |
like widgets, animations in flutter work with composition. |
when building the widget tree you assign the animation to an animated |
property of a widget, such as the opacity of a FadeTransition, and tell the |
controller to start the animation. |
the following example shows how to write a FadeTransition that fades the |
widget into a logo when you press the FloatingActionButton: |
<code_start> |
import 'package:flutter/material.dart'; |
void main() { |
runApp(const FadeAppTest()); |
} |
class FadeAppTest extends StatelessWidget { |
const FadeAppTest({super.key}); |
// this widget is the root of your application. |
@override |
widget build(BuildContext context) { |
return MaterialApp( |
title: 'fade demo', |
theme: ThemeData( |
colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple), |
), |
home: const MyFadeTest(title: 'fade demo'), |
); |
} |
} |
class MyFadeTest extends StatefulWidget { |
const MyFadeTest({super.key, required this.title}); |
final string title; |
@override |
State<MyFadeTest> createState() => _MyFadeTest(); |
} |
class _MyFadeTest extends State<MyFadeTest> with TickerProviderStateMixin { |
late AnimationController controller; |
late CurvedAnimation curve; |
@override |
void initState() { |
super.initState(); |
controller = AnimationController( |
duration: const duration(milliseconds: 2000), |
vsync: this, |
); |
curve = CurvedAnimation( |
parent: controller, |
curve: Curves.easeIn, |
); |
} |