The user can cancel a drag at any time by pressing the key represented by XkCancel. In this case, the source adapter and the target adapter (if any) activate their dragCancelCallback. The callData for this callback depends on whether the adapter is a source or a target adapter. For source adapters, the callData includes the same information as the callData for the dragCompleteCallback. For target adapters, the callData includes the same information as the callData for the dropCallback.

The source adapter also activates the dragCancelCallback when items are dropped outside any target widgets. The dragCancelCallback is also triggered when the items are dropped onto a target that is unwilling to accept them; that is, when no valid operation is in effect or when the target widget's application sets the doit flag to false in the dropCallback's callData.