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// this widget is the root of your application.
const SampleApp({super.key});
@override
widget build(BuildContext context) {
return const MaterialApp(
title: 'fade demo',
home: 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 SingleTickerProviderStateMixin {
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
void dispose() {
controller.dispose();
super.dispose();
}
@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(
onPressed: () {
controller.forward();
},
tooltip: 'fade',
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>
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
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,