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}<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,
);
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: FadeTransition(
opacity: curve,
child: const FlutterLogo(
size: 100,
),
),
),
floatingActionButton: FloatingActionButton(
tooltip: 'Fade',
onPressed: () {
controller.forward();
},
child: const Icon(Icons.brush),
),
);
}
}<code_end>
For more information, see
Animation & Motion widgets,
the Animations tutorial,
and the Animations overview.<topic_end>
<topic_start>
How do I use a Canvas to draw/paint?
In Android, you would use the Canvas and Drawable
to draw images and shapes to the screen.
Flutter has a similar Canvas API as well,
since it’s based on the same low-level rendering engine, Skia.
As a result, painting to a canvas in Flutter
is a very familiar task for Android developers.Flutter has two classes that help you draw to the canvas: CustomPaint
and CustomPainter,
the latter of which implements your algorithm to draw to the canvas.To learn how to implement a signature painter in Flutter,
see Collin’s answer on Custom Paint.
<code_start>import 'package:flutter/material.dart';
void main() => runApp(const MaterialApp(home: DemoApp()));
class DemoApp extends StatelessWidget {
const DemoApp({super.key});