PathMeasure pathMeasure = new PathMeasure();

PathMeasure pathMeasure = new PathMeasure(path, forceClosed);

pathMeasure.setPath(path, forceClosed);

float length = pathMeasure.getLength();

pathMeasure.getSegment(start, stop, mDstPath, true);

  mPath = new Path();
  mDst = new Path();

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
 mPath.addCircle(w / 2, h / 2, mRadius, Path.Direction.CW);
 mPathMeasure = new PathMeasure();
 mPathMeasure.setPath(mPath, false);
 mPathLength = mPathMeasure.getLength();
}

private void startAnim() {
 ValueAnimator anim = ValueAnimator.ofFloat(0, 1);
 anim.setInterpolator(new DecelerateInterpolator());
 anim.setRepeatCount(ValueAnimator.INFINITE);
 anim.setDuration(mAnimDuration);
 anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
  @Override
  public void onAnimationUpdate(ValueAnimator animation) {
   mPathPercent = (float) animation.getAnimatedValue();
   invalidate();
  }
 });
 anim.start();

 //再加一个旋转动画以及两倍的时长，形成旋转视差
 ObjectAnimator animRotate = ObjectAnimator.ofFloat(this, View.ROTATION, 0, 360);
 animRotate.setInterpolator(new LinearInterpolator());
 animRotate.setRepeatCount(ValueAnimator.INFINITE);
 animRotate.setDuration(2 * mAnimDuration);
 animRotate.start();
}

@Override
protected void onDraw(Canvas canvas) {
 float stop = mPathLength * mPathPercent;
 float start = (float) (stop - ((0.5 - Math.abs(mPathPercent - 0.5)) * mPathLength * 4));
 mDst.reset();
//  mDst.lineTo(0, 0);
 mPathMeasure.getSegment(start, stop, mDst, true);
 canvas.drawPath(mDst, mPaint);
}

 public void start() {
  mIsLoading = true;
  setVisibility(View.VISIBLE);
  startAnim();
 }

 public void stop() {
  mIsLoading = false;
  setVisibility(View.GONE);
 }

 public boolean isLoading() {
  return mIsLoading;
 }

Button btn = (Button) findViewById(R.id.btn);
btn.setOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(View v) {
  if (loadingView.isLoading()) {
   loadingView.stop();
  } else {
   loadingView.start();
  }
 }
});