Flutter实例代码：波浪圆形进度条

效果图文章源自菜鸟学院-https://www.cainiaoxueyuan.com/xcx/13602.html

实现步骤

绘制进度条

1. 先绘制绘制波浪

    void drawWave(Canvas canvas, Offset center, double radius,
        double waveOffsetPercent, Paint paint) {
      double waveOffset = -(waveOffsetPercent * radius * 2);
      //对画布进行圆形裁剪
      canvas.save();
      Path clipPath = Path()
        ..addOval(Rect.fromCircle(center: center, radius: radius));
      canvas.clipPath(clipPath);
    
      //表示出上图所示的point(上图中p)以及controlPoint（上图中c）
      double waveProgressHeightY = (1 - percent) * radius * 2;
      Offset point1 = Offset(waveOffset, waveProgressHeightY);
      Offset point2 = Offset(waveOffset + radius, waveProgressHeightY);
      Offset point3 = Offset(waveOffset + radius * 2, waveProgressHeightY);
      Offset point4 = Offset(waveOffset + radius * 3, waveProgressHeightY);
      Offset point5 = Offset(waveOffset + radius * 4, waveProgressHeightY);
      Offset point6 = Offset(point5.dx, radius * 2 + halfWaveHeight);
      Offset point7 = Offset(point1.dx, radius * 2 + halfWaveHeight);
      Offset controlPoint1 =
          Offset(waveOffset + radius * 0.5, waveProgressHeightY - halfWaveHeight);
      Offset controlPoint2 =
          Offset(waveOffset + radius * 1.5, waveProgressHeightY + halfWaveHeight);
      Offset controlPoint3 =
          Offset(waveOffset + radius * 2.5, waveProgressHeightY - halfWaveHeight);
      Offset controlPoint4 =
          Offset(waveOffset + radius * 3.5, waveProgressHeightY + halfWaveHeight);
      //完成path的链接
      Path wavePath = Path()
        ..moveTo(point1.dx, point1.dy)
        ..quadraticBezierTo(
            controlPoint1.dx, controlPoint1.dy, point2.dx, point2.dy)
        ..quadraticBezierTo(
            controlPoint2.dx, controlPoint2.dy, point3.dx, point3.dy)
        ..quadraticBezierTo(
            controlPoint3.dx, controlPoint3.dy, point4.dx, point4.dy)
        ..quadraticBezierTo(
            controlPoint4.dx, controlPoint4.dy, point5.dx, point5.dy)
        ..lineTo(point6.dx, point6.dy)
        ..lineTo(point7.dx, point7.dy)
        ..close();
      //完成绘制
      canvas.drawPath(wavePath, paint);
      canvas.restore();
    }
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2. 绘制层叠的波浪，跟第一步一样的绘制方法，可以将颜色与偏移值跟第一个波浪错开
3. 绘制圆形进度内容，这一步需要注意的是在绘制进度的时候，需要对画布进行旋转，具体绘制内容如下

    void drawCircleProgress(
        Canvas canvas,
        Offset center,
        double radius,
        Size size) {
      //画进度条圆框背景
      canvas.drawCircle(center, radius, circleProgressBGPaint);
      //保存画布状态
      canvas.save();
      //逆时针旋转画布90度
      canvas.rotate(degreeToRadian(-90));
      canvas.translate(
          -(size.height + size.width) / 2, -(size.height - size.width) / 2);
      //画进度条圆框进度
      canvas.drawArc(
          Rect.fromCircle(center: center, radius: radius),
          degreeToRadian(0),
          degreeToRadian(percent * 360),
          false,
          circleProgressPaint);
      //恢复画布状态
      canvas.restore();
    }
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绘制工作基本就差不多完成了文章源自菜鸟学院-https://www.cainiaoxueyuan.com/xcx/13602.html

让波浪动起来

利用动画更改波浪的偏移值，并使动画不停的进行重复。两个波浪偏移的速度设置成不一致的，让波浪看起来更协调文章源自菜鸟学院-https://www.cainiaoxueyuan.com/xcx/13602.html

  void initState() {
    super.initState();
    waveAnimation = AnimationController(
      vsync: this,
      duration: widget.waveAnimationDuration,
    );
    waveAnimation.addListener(waveAnimationListener);
    lightWaveAnimation = AnimationController(
      vsync: this,
      duration: widget.lightWaveAnimationDuration,
    );
	//在lightWaveAnimationListener中获取波浪最新的偏移值，刷新状态
    lightWaveAnimation.addListener(lightWaveAnimationListener);
    waveAnimation.repeat();
    lightWaveAnimation.repeat();
  }
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完成波浪动起来的效果之后基本上就差不多了，但是会有一个很明显的问题，那就是在设置进度之后，进度条中的波浪是瞬间涨上去，看上去非常的不协调，所以我们还需要给进度条加上一个，进度更改时的动画效果。文章源自菜鸟学院-https://www.cainiaoxueyuan.com/xcx/13602.html

让波浪缓缓升起来降下去

  @override
  void initState() {
    super.initState();
    controller = AnimationController(
        vsync: this, duration: widget.progressAnimatedDuration);
    controller.addStatusListener((status) {
	  //当动画结束时重置动画
      if (status == AnimationStatus.completed) {
        progressAnimation.removeListener(handleProgressChange);
        controller.reset();
      }
    });
  }

  @override
  Widget build(BuildContext context) {
	//当进度发生改变时，开始动画
    if (currentValue != widget.value && !controller.isAnimating) {
      progressAnimation =
          controller.drive(IntTween(begin: currentValue, end: widget.value));
      progressAnimation.addListener(handleProgressChange);
      controller.forward();
    }
    ...
  }
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在进度改变时，我们通过一个动画来改变进度到指定的进度，这样就保证了，进度发生改变时，波浪不会瞬间涨上去。文章源自菜鸟学院-https://www.cainiaoxueyuan.com/xcx/13602.html