可以说一下实现的思路么，我看源码那个缩放比例看了好久，没有注释

[kaka-gk]

      if ((!mIsFinished) && (mScale > 1.0D)) {
                float currentThreadTime=SystemClock.currentThreadTimeMillis();
                               float f1 = ((float) SystemClock.currentThreadTimeMillis()- 

(float) mStartTime) / (float) mDuration;
f2 = mScale - (mScale - 1.0F) * PullToZoomScrollViewEx.sInterpolator.getInterpolation(f1);