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// this widget is the root of your application.
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const SampleApp({super.key});
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@override
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widget build(BuildContext context) {
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return const MaterialApp(
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title: 'fade demo',
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home: MyFadeTest(title: 'fade demo'),
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);
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}
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}
|
class MyFadeTest extends StatefulWidget {
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const MyFadeTest({super.key, required this.title});
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final string title;
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@override
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State<MyFadeTest> createState() => _MyFadeTest();
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}
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class _MyFadeTest extends State<MyFadeTest>
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with SingleTickerProviderStateMixin {
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late AnimationController controller;
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late CurvedAnimation curve;
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@override
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void initState() {
|
super.initState();
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controller = AnimationController(
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duration: const duration(milliseconds: 2000),
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vsync: this,
|
);
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curve = CurvedAnimation(
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parent: controller,
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curve: Curves.easeIn,
|
);
|
}
|
@override
|
void dispose() {
|
controller.dispose();
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super.dispose();
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}
|
@override
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widget build(BuildContext context) {
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return scaffold(
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appBar: AppBar(title: text(widget.title)),
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body: center(
|
child: FadeTransition(
|
opacity: curve,
|
child: const FlutterLogo(size: 100),
|
),
|
),
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floatingActionButton: FloatingActionButton(
|
onPressed: () {
|
controller.forward();
|
},
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tooltip: 'fade',
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child: const Icon(Icons.brush),
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),
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);
|
}
|
}
|
<code_end>
|
for more information, see animation & motion widgets,
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the animations tutorial, and the animations overview.
|
<topic_end>
|
<topic_start>
|
drawing on the screen
|
in UIKit, you use CoreGraphics to draw lines and shapes to the
|
screen. flutter has a different API based on the canvas class,
|
with two other classes that help you draw: 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 StackOverflow.
|
<code_start>
|
import 'package:flutter/material.dart';
|
void main() => runApp(const MaterialApp(home: DemoApp()));
|
class DemoApp extends StatelessWidget {
|
const DemoApp({super.key});
|
@override
|
widget build(BuildContext context) => const scaffold(body: signature());
|
}
|
class signature extends StatefulWidget {
|
const signature({super.key});
|
@override
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State<Signature> createState() => SignatureState();
|
}
|
class SignatureState extends State<Signature> {
|
List<Offset?> _points = <offset?>[];
|
@override
|
widget build(BuildContext context) {
|
return GestureDetector(
|
onPanUpdate: (details) {
|
setState(() {
|
RenderBox? referenceBox = context.findRenderObject() as RenderBox;
|
offset localPosition =
|
referenceBox.globalToLocal(details.globalPosition);
|
_points = List.from(_points)..add(localPosition);
|
});
|
},
|
onPanEnd: (details) => _points.add(null),
|
child:
|
CustomPaint(
|
painter: SignaturePainter(_points),
|
size: size.infinite,
|
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