I use DragDropManager to drag & drop items between RadListBoxe A and RadListBox B. It works good. But it will cause the program crashed when I try following:
Because the RadListBox B is not allowed to have TWO items on the same time, so existing item must be "swap" by new one. I remove the existing item and replaced by new one via code. It works good only when it drops under existing item. And, when I drop the new item before the existing item, the program will be crashed by NullReferenceException, I found the exception caused by DragDropBehaviour<TSTate> class. See screenshots provided.
Please, solutions, urgent.