Flutter小球弹跳动画

import 'package:flutter/material.dart';
void main() {
  runApp(MaterialApp(
    home: Scaffold(body: GameWidget()),
  ));
}
class GameWidget extends StatefulWidget {
  @override
  _GameWidgetState createState() => _GameWidgetState();
}
class _GameWidgetState extends State<GameWidget>
    with SingleTickerProviderStateMixin {
  late AnimationController controller;
  late Animation<double> animation;
  @override
  void initState() {
    super.initState();
    controller = AnimationController(
      duration: const Duration(seconds: 2),
      vsync: this,
    )..repeat(reverse: true);
    animation = Tween<double>(begin: 0, end: 200).animate(controller);
  }
  @override
  Widget build(BuildContext context) {
    return AnimatedBuilder(
      animation: animation,
      builder: (context, child) {
        return CustomPaint(
          painter: BallPainter(animation.value),
        );
      },
    );
  }
}
class BallPainter extends CustomPainter {
  final double height;
  BallPainter(this.height);
  @override
  void paint(Canvas canvas, Size size) {
    final paint = Paint()..color = Colors.blue;
    final ballSize = 50.0;
    final ballPosition = Offset(0, size.height - height - ballSize / 2);
    canvas.drawCircle(ballPosition, ballSize / 2, paint);
  }
  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) {
    final oldPainter = oldDelegate as BallPainter;
    return oldPainter.height != height;
  }
}