public class WaveView extends View {
  private Paint mPaint;
  private final Path mPath;
  //波長
  private int wavelength = 500;
  private int originY=800;
  private int dx,dy;
 
  public WaveView(Context context, @Nullable AttributeSet attrs) {
    super(context, attrs);
    mPaint = new Paint();
    mPath = new Path();
    mPaint.setColor(Color.GREEN);
    mPaint.setStrokeWidth(5);
    mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
//    startanimation();
  }
 
 
  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    //重置path
    mPath.reset();
//    改變y的起始坐標
    if(dy<originY+150){
      dy+=10;
    }
 
    int halfWaveLength = wavelength / 2;
    mPath.moveTo(-wavelength + dx, originY-dy);
    //屏幕多寬，畫多少
    for (int i = -wavelength; i <= getWidth() + wavelength; i += wavelength) {
      /**
       * 相對繪制二階貝塞爾曲線（相對于自己的起始點--也即是上一個曲線的終點 ）
       * float dx1 相對于上一個曲線的終點 的距離
       * float dy1
       * float dx2
       * float dy2
       */
      mPath.rQuadTo(halfWaveLength / 2, -150, halfWaveLength, 0);
      mPath.rQuadTo(halfWaveLength / 2, 150, halfWaveLength, 0);
 
    }
    //顏色填充
    //畫一個封閉的空間
    mPath.lineTo(getWidth(), getHeight());
    mPath.lineTo(0, getHeight());
    mPath.close();
    canvas.drawPath(mPath, mPaint);
//    //設置起始點坐標
//    path.moveTo(100,400);
//    //二階貝塞爾曲線1
//    path.quadTo(250,200,400,400);
//    //二階貝塞爾曲線2
//    path.quadTo(550,600,700,400);
//    //關閉路徑（將起點和終點閉合）
//    path.close();
//    path.moveTo(100,700);
//    path.cubicTo(50,500,550,500,700,700);
 
  }
 
  public void startanimation() {
    ValueAnimator animator = ValueAnimator.ofInt(0, wavelength);
    animator.setDuration(1000);
    animator.setInterpolator(new LinearInterpolator());
    //無限循環(huán)
    animator.setRepeatCount(ValueAnimator.INFINITE);
    animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
      @Override
      public void onAnimationUpdate(ValueAnimator animation) {
        dx = (int) animation.getAnimatedValue();
        postInvalidate();
      }
    });
    animator.start();
  }
}