『Flutter-绘制篇』实现炫酷的雨雪特效

import 'dart:math' as math;
import 'package:flutter/material.dart';
 
class RainSnowEffect extends StatefulWidget {
  @override
  _RainSnowEffectState createState() => _RainSnowEffectState();
}
 
class _RainSnowEffectState extends State<RainSnowEffect>
    with SingleTickerProviderStateMixin {
  AnimationController _controller;
  List<Drop> _drops = [];
 
  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      duration: const Duration(seconds: 10),
      vsync: this,
    )..addListener(() {
        setState(() {
          _drops.forEach((drop) => drop.update(1.0 / _controller.duration.inMilliseconds));
        });
      });
    _controller.forward();
  }
 
  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }
 
  @override
  Widget build(BuildContext context) {
    if (_drops.length < 200) {
      _drops.add(Drop(random: math.Random()));
    }
    return Scaffold(
      body: Stack(
        children: _drops.map((drop) {
          return Positioned(
            left: drop.x,
            top: drop.y,
            child: drop.isRaining ? Rain() : Snow(),
          );
        }).toList(),
      ),
    );
  }
}
 
class Drop {
  double x;
  double y;
  double dx;
  bool isRaining;
 
  Drop({math.Random random}) {
    x = random.nextDouble() * 375;
    y = random.nextDouble() * 600;
    dx = random.nextDouble() * 1.5 + 0.5;
    isRaining = random.nextBool();
  }
 
  void update(double dt) {
    x += dx * dt;
    y += dt / 20;
    if (y > 600) {
      y = -50;
      isRaining = !isRaining;
    }
  }
}
 
class Rain extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      width: 5,
      height: 20,
      decoration: BoxDecoration(
        color: Colors.blue,
        shape: BoxShape.circle,
      ),
    );
  }
}
 
class Snow extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      width: 5,
      height: 5,
      decoration: BoxDecoration(
        color: Colors.white,
        shape: BoxShape.circle,
      ),
    );
  }
}

这段代码实现了在Flutter中创建一个雨雪特效的示例。它使用了AnimationController来控制水滴的更新，并且通过随机值确定水滴的起始位置、速度以及是雨还是雪。当水滴移动到屏幕外部时，会重新生成新的位置和形态。这个例子展示了如何使用Widget、AnimationController和状态管理来创建一个动态的视觉效