问题:
Flutter 如何实现一个心跳动画? 如 GIF 所示:
解决方法:
可以使用 CustomPainter 或者 SpriteWidget.
import 'dart:math'; import 'package:flutter/material.dart'; class SpritePainter extends CustomPainter { final Animation<double> _animation; SpritePainter(this._animation) : super(repaint: _animation); void circle(Canvas canvas, Rect rect, double value) { double opacity = (1.0 - (value / 4.0)).clamp(0.0, 1.0); Color color = new Color.fromRGBO(0, 117, 194, opacity); double size = rect.width / 2; double area = size * size; double radius = sqrt(area * value / 4); final Paint paint = new Paint()..color = color; canvas.drawCircle(rect.center, radius, paint); } @override void paint(Canvas canvas, Size size) { Rect rect = new Rect.fromLTRB(0.0, 0.0, size.width, size.height); for (int wave = 3; wave >= 0; wave--) { circle(canvas, rect, wave + _animation.value); } } @override bool shouldRepaint(SpritePainter oldDelegate) { return true; } } class SpriteDemo extends StatefulWidget { @override SpriteDemoState createState() => new SpriteDemoState(); } class SpriteDemoState extends State<SpriteDemo> with SingleTickerProviderStateMixin { AnimationController _controller; @override void initState() { super.initState(); _controller = new AnimationController( vsync: this, ); //_startAnimation(); } @override void dispose() { _controller.dispose(); super.dispose(); } void _startAnimation() { _controller.stop(); _controller.reset(); _controller.repeat( period: Duration(seconds: 1), ); } @override Widget build(BuildContext context) { return new Scaffold( appBar: new AppBar(title: const Text('Pulse')), body: new CustomPaint( painter: new SpritePainter(_controller), child: new SizedBox( width: 200.0, height: 200.0, ), ), floatingActionButton: new FloatingActionButton( onPressed: _startAnimation, child: new Icon(Icons.play_arrow), ), ); } } void main() { runApp( new MaterialApp( home: new SpriteDemo(), ), ); }