java在拖动ListView边缘时如何检测？

Question

我不知道在拖动ListView边缘时如何检测

http://imgur.com/PCCgkEC

//编辑

事件1-面板上的listview

事件2-主面板

    event1.setOnTouchListener(new View.OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {
             if ( ##listview on top end when we drag to down ) {
                  return event2.onTouchEvent(event);
             } else {
                  return event1.onTouchEvent(event)
             }
        }
    });