Easiest way is to use a UIPanGestureRecognizer. That will give you messages when the view is moved and when it is dropped. When it is moved, update its center. When it is dropped, check if its position is within the bounds of the view you want to drop in. (You might need to convert coordinates to the target view's coordinate system.) If it is, do the appropriate action.
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
