Question

I only noticed this because I mistakenly tried to attach a DragEventHandler to a DragLeave event. I was surprised to see that the DragLeave Event was just as a general EventHandler. This is odd to me because both the DragDrop Event and the DragEnter Event use DragEventHandlers. Is there a reason or explanation for this?

Resources:

http://msdn.microsoft.com/en-us/library/system.windows.forms.control.dragleave http://msdn.microsoft.com/en-us/library/system.windows.forms.control.dragenter http://msdn.microsoft.com/en-us/library/system.windows.forms.control.dragdrop

Answer 1

Yes. When handling DragEnter or DragDrop, we usually require or update additional information (such as the current drag effect, the active modifier keys, or the actual data involved). Therefore, the event argument passed to the handler has to provide access to that information.

On the other hand, there is not much we can (or should) do on DragLeave. We cannot cancel a leave. We cannot change the drag engine’s behavior or the mouse pointer’s shape because it’s, well, a leave, the system’s way of telling us thank you for your cooperation, we're done now, maybe we'll get in touch with you again in the future.