prepareForDrop
Called by the ItemTouchHelper after a View is dropped over another View.
A LayoutManager should implement this interface to get ready for the upcoming move operation.
For example, LinearLayoutManager sets up a "scrollToPositionWithOffset" calls so that the View under drag will be used as an anchor View while calculating the next layout, making layout stay consistent.
Parameters
The View which is being dragged. It is very likely that user is still dragging this View so there might be other calls to prepareForDrop() after this one.
The target view which is being dropped on.
The left offset of the View that is being dragged. This value includes the movement caused by the user.
The top offset of the View that is being dragged. This value includes the movement caused by the user.