flutter自定义波浪view

void main() => runApp(WaveWidget(
      bgColor: Colors.lightBlue,
//       imageProvider: AssetImage('assets/pic/ic_headimg.png'),
//       imgSize: Size(50.0, 0.0),
      size: Size(300.0, 500.0),
    ));



 WaveWidget(
      {this.imageProvider,
      @required this.size,
      this.imgSize = const Size(60.0, 60.0),
      this.imgOffset = const Offset(0.0, 0.0),
      this.waveAmplitude = 10.0,
      this.waveFrequency = 1.6,
      this.wavePhase = 10.0,
      this.bgColor,
      this.rountImg = true,
      this.heightPercentange = 6 / 7});

1.自定义view动画的步骤

原生自定义view是继承view，重写onMeasure和Ondraw方法，在ondraw中在canvas中画出图形，再通过Animator控制变量值，来达到动画效果

flutter 是继承CustomPainter 实现paint方法，在paint方法中画出图形，再通过AntimationController控制变量值，达到动画效果。再将CustomPainter 实例作为参数传给CustomPaint，就达成了。

由于都出自google 重原生ondraw方法移植到flutter的paint方法十分容易。两者的Canvas，Paint，Path等类Api都是很相似。

---

开始移植工作

1. 原理

学过物理的都知道正旋波等，声波的概念。

• [y=A*sin(Wt+ Q];
• 可以通过A控制振幅，W控制频率，Q控制x轴位移
• 在控制A和w都不变的情况下，先画好静态波浪，我们只需要讲Q换成变量，然后用动画控制偏移量，达到波移动的效果

画出波浪

• 把画板假象为带有一个坐标轴
• 最左边为x=0处，view底部或波浪中部作为y=0处
• 计算x->屏幕宽度取值下的y的值，将这些点加入到一个path，就绘制出了波浪线,多个波纹，用同样的方法

    path1.moveTo(0.0,viewCenterY -waveAmplitude * _getSinY(wavePhaseValue.value, waveFrequency, -1));
    for (int i = 0; i < size.width - 1; i++) {
      path1.lineTo((i + 1).toDouble(), viewCenterY -waveAmplitude * _getSinY(wavePhaseValue.value, waveFrequency, (i + 1)));
    }
    path1.lineTo(size.width, size.height);
    path1.lineTo(0.0, size.height);
    path1.close();

动画控制

• 初始化一个AnimationController，并将其作为参数传给CustomPainter的repaint。它将自动监听controller的动画驱动值，重绘调用paint方法
• 新建一个Tween动画，将控制位移的动画值Animation传给paint，paint中取这个动画值来绘制，就实现了动画效果

 _waveControl =new AnimationController(vsync: this, duration: Duration(seconds: 2));
_wavePhaseValue =Tween(begin: widget.wavePhase, end: 360 + widget.wavePhase)
                 .animate(_waveControl);
 _wavePhaseValue.addStatusListener((s) {
      if (s == AnimationStatus.completed) {
        _waveControl.reset();
        _waveControl.forward();
      }
    });
    _waveControl.forward();

 Copyright [2018] [While1true]

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
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       http://www.apache.org/licenses/LICENSE-2.0

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   distributed under the License is distributed on an "AS IS" BASIS,
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