void CancelTransfer()
 {
     if (copyObject != null) {
         object oldCopyObject = copyObject;
         copyObject = null;
         if (currentTransferOperation == DragOperation.Move) {
             TreeBuilder tb = new TreeBuilder (this);
             if (tb.MoveToObject (oldCopyObject))
                 tb.Update ();
         }
     }
 }
        public void CutCurrentItem()
        {
            CancelTransfer ();
            TransferCurrentItem (DragOperation.Move);

            if (copyObject != null) {
                TreeBuilder tb = new TreeBuilder (this);
                if (tb.MoveToObject (copyObject))
                    tb.Update ();
            }
        }