@Override
        public void onFling(float startX, float startY, float velocityX, float velocityY) {
            mCurrentFlingRunnable = new FlingRunnable(mImageView.getContext());
            mCurrentFlingRunnable.fling(getImageViewWidth(mImageView),
                    getImageViewHeight(mImageView), (int) velocityX, (int) velocityY);
            mImageView.post(mCurrentFlingRunnable);
        }
The component of {@link PhotoView} which does the work allowing for zooming, scaling, panning, etc.
It is made public in case you need to subclass something other than {@link ImageView} and still
gain the functionality that {@link PhotoView} offers
main/src/main/java/com/quxianggif/common/view/photoview/PhotoViewAttacher.java