@Override
  public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
    return mDelegate.onScroll(e1, e2, distanceX, distanceY);
  }
Wrapper for SimpleOnGestureListener as GestureDetector does not allow changing its listener.
samples/zoomable/src/main/java/com/facebook/samples/zoomable/GestureListenerWrapper.java