Called by the framework when the mouse first enters the non-scrolling region of the drop target window.
A value from the DROPEFFECT enumerated type, which indicates the type of drop that would occur if the user dropped the object at this position. The type of drop usually depends on the current key state indicated by dwKeyState. A standard mapping of keystates to DROPEFFECT values is:
DROPEFFECT_NONE The data object cannot be dropped in this window.
DROPEFFECT_LINK for MK_CONTROL | MK_SHIFT Creates a linkage between the object and its server.
DROPEFFECT_COPY for MK_CONTROL Creates a copy of the dropped object.
DROPEFFECT_MOVE for MK_ALT Creates a copy of the dropped object and delete the original object. This is typically the default drop effect, when the view can accept this data object.
For more information, see the MFC Advanced Concepts sample OCLIENT.
Default implementation is to do nothing and return DROPEFFECT_NONE.
Override this function to prepare for future calls to the OnDragOver member function. Any data required from the data object should be retrieved at this time for later use in the OnDragOver member function. The view should also be updated at this time to give the user visual feedback. For more information, see the article Drag and Drop: Implementing a Drop Target.