/** Installs a gesture detector to the given controller. */
 protected void maybeBuildAndSetGestureDetector(AbstractDraweeController controller) {
   GestureDetector gestureDetector = controller.getGestureDetector();
   if (gestureDetector == null) {
     gestureDetector = GestureDetector.newInstance(mContext);
     controller.setGestureDetector(gestureDetector);
   }
 }