NullReferenceException in DragDropBehaviour<TSTate> class

[Jun]

Hallo,

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.

Tam

 

[Martin Ivanov]

Hello Jun,

Can you show how exactly do you implement the swap of the items in code? Also, can you share how the listboxes are setup in XAML and in code?

Regards,
Martin Ivanov
Progress Telerik