【Flutter 实战】自定义动画-涟漪和雷达扫描

秒速五厘米 2022-12-01 05:13 368阅读 0赞

![20200826065913300.png][]

> 老孟导读：此篇文章是 Flutter 动画系列文章第五篇，本文介绍2个自定义动画：**涟漪**和**雷达扫描**效果。

## 涟漪 ##

实现涟漪动画效果如下：

![20200826065913571.png][]

此动画通过 **CustomPainter** 绘制配合 **AnimationController** 动画控制实现，定义动画控制部分：

class WaterRipple extends StatefulWidget {
      final int count;
      final Color color;
    
      const WaterRipple({Key key, this.count = 3, this.color = const Color(0xFF0080ff)}) : super(key: key);
    
      @override
      _WaterRippleState createState() => _WaterRippleState();
    }
    
    class _WaterRippleState extends State<WaterRipple>
        with SingleTickerProviderStateMixin {
      AnimationController _controller;
    
      @override
      void initState() {
        _controller =
            AnimationController(vsync: this, duration: Duration(milliseconds: 2000))
              ..repeat();
        super.initState();
      }
    
      @override
      void dispose() {
        _controller.dispose();
        super.dispose();
      }
    
      @override
      Widget build(BuildContext context) {
        return AnimatedBuilder(
          animation: _controller,
          builder: (context, child) {
            return CustomPaint(
              painter: WaterRipplePainter(_controller.value,count: widget.count,color: widget.color),
            );
          },
        );
      }
    }

**count** 和 **color** 分别代表水波纹的数量和颜色。

**WaterRipplePainter** 定义如下：

class WaterRipplePainter extends CustomPainter {
      final double progress;
      final int count;
      final Color color;
    
      Paint _paint = Paint()..style = PaintingStyle.fill;
    
      WaterRipplePainter(this.progress,
          {this.count = 3, this.color = const Color(0xFF0080ff)});
    
      @override
      void paint(Canvas canvas, Size size) {
        double radius = min(size.width / 2, size.height / 2);
    
        for (int i = count; i >= 0; i--) {
          final double opacity = (1.0 - ((i + progress) / (count + 1)));
          final Color _color = color.withOpacity(opacity);
          _paint..color = _color;
    
          double _radius = radius * ((i + progress) / (count + 1));
    
          canvas.drawCircle(
              Offset(size.width / 2, size.height / 2), _radius, _paint);
        }
      }
    
      @override
      bool shouldRepaint(CustomPainter oldDelegate) {
        return true;
      }
    }

重点是 **paint** 方法，根据动画进度计算颜色的透明度和半径。

使用如下：

class WaterRipplePage extends StatelessWidget {
      @override
      Widget build(BuildContext context) {
        return Scaffold(
          body: Center(
              child: Container(height: 200, width: 200, child: WaterRipple())),
        );
      }
    }

## 雷达扫描 ##

实现雷达扫描效果：

![20200826065913697.png][]

此效果分为两部分：中间的 logo 图片和扫描部分。

### 中间的 logo 图片 ###

中间的 logo 图片边缘有阴影效果，像是太阳发光一样，实现：

Container(
      height: 70.0,
      width: 70.0,
      decoration: BoxDecoration(
          color: Colors.grey,
          image: DecorationImage(
              image: AssetImage('assets/images/logo.png')),
          shape: BoxShape.circle,
          boxShadow: [
            BoxShadow(
              color: Colors.white.withOpacity(.5),
              blurRadius: 5.0,
              spreadRadius: 3.0,
            ),
          ]),
    )

![Image 1][]

### 扫描 ###

定义雷达扫描的动画控制器：

class RadarView extends StatefulWidget {
      @override
      _RadarViewState createState() => _RadarViewState();
    }
    
    class _RadarViewState extends State<RadarView>
        with SingleTickerProviderStateMixin {
      AnimationController _controller;
      Animation<double> _animation;
    
      @override
      void initState() {
        _controller =
            AnimationController(vsync: this, duration: Duration(seconds: 5));
        _animation = Tween(begin: .0, end: pi * 2).animate(_controller);
        _controller.repeat();
        super.initState();
      }
    
      @override
      void dispose() {
        _controller.dispose();
        super.dispose();
      }
    
      @override
      Widget build(BuildContext context) {
        return AnimatedBuilder(
          animation: _animation,
          builder: (context, child) {
            return CustomPaint(
              painter: RadarPainter(_animation.value),
            );
          },
        );
      }
    }

**RadarPainter** 定义如下：

class RadarPainter extends CustomPainter {
      final double angle;
    
      Paint _bgPaint = Paint()
        ..color = Colors.white
        ..strokeWidth = 1
        ..style = PaintingStyle.stroke;
    
      Paint _paint = Paint()..style = PaintingStyle.fill;
    
      int circleCount = 3;
    
      RadarPainter(this.angle);
    
      @override
      void paint(Canvas canvas, Size size) {
        var radius = min(size.width / 2, size.height / 2);
    
        canvas.drawLine(Offset(size.width / 2, size.height / 2 - radius),
            Offset(size.width / 2, size.height / 2 + radius), _bgPaint);
        canvas.drawLine(Offset(size.width / 2 - radius, size.height / 2),
            Offset(size.width / 2 + radius, size.height / 2), _bgPaint);
    
        for (var i = 1; i <= circleCount; ++i) {
          canvas.drawCircle(Offset(size.width / 2, size.height / 2),
              radius * i / circleCount, _bgPaint);
        }
    
        _paint.shader = ui.Gradient.sweep(
            Offset(size.width / 2, size.height / 2),
            [Colors.white.withOpacity(.01), Colors.white.withOpacity(.5)],
            [.0, 1.0],
            TileMode.clamp,
            .0,
            pi / 12);
    
        canvas.save();
        double r = sqrt(pow(size.width, 2) + pow(size.height, 2));
        double startAngle = atan(size.height / size.width);
        Point p0 = Point(r * cos(startAngle), r * sin(startAngle));
        Point px = Point(r * cos(angle + startAngle), r * sin(angle + startAngle));
        canvas.translate((p0.x - px.x) / 2, (p0.y - px.y) / 2);
        canvas.rotate(angle);
    
        canvas.drawArc(
            Rect.fromCircle(
                center: Offset(size.width / 2, size.height / 2), radius: radius),
            0,
            pi / 12,
            true,
            _paint);
        canvas.restore();
      }
    
      @override
      bool shouldRepaint(CustomPainter oldDelegate) {
        return true;
      }
    }

将两者结合在一起：

class RadarPage extends StatelessWidget {
      @override
      Widget build(BuildContext context) {
        return Scaffold(
            backgroundColor: Color(0xFF0F1532),
            body: Stack(
              children: [
                Positioned.fill(
                  left: 10,
                  right: 10,
                  child: Center(
                    child: Stack(children: [
                      Positioned.fill(
                        child: RadarView(),
                      ),
                      Positioned(
                        child: Center(
                          child: Container(
                            height: 70.0,
                            width: 70.0,
                            decoration: BoxDecoration(
                                color: Colors.grey,
                                image: DecorationImage(
                                    image: AssetImage('assets/images/logo.png')),
                                shape: BoxShape.circle,
                                boxShadow: [
                                  BoxShadow(
                                    color: Colors.white.withOpacity(.5),
                                    blurRadius: 5.0,
                                    spreadRadius: 3.0,
                                  ),
                                ]),
                          ),
                        ),
                      ),
                    ]),
                  ),
                )
              ],
            ));
      }
    }

## 交流 ##

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[20200826065913300.png]: /images/20221123/78dc7833d9624638a0c33a57a5067ca1.png
[20200826065913571.png]: /images/20221123/cbecdebd38d04b12a78f3651d40af17e.png
[20200826065913697.png]: /images/20221123/18f76e8a3afb4de0979fa95c1f0f8504.png
[Image 1]: 
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