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DoDragDrop
Carries out an OLE drag and drop operation.
HRESULT DoDragDrop(
IDataObject * pDataObject,
| //Data object being dragged
| IDropSource * pDropSource,
| //Instance of IDropSource for source application
| DWORD dwOKEffect,
| //Specifies the effects allowed by the source
| DWORD * pdwEffect
| //Points to effects of the OLE drag and drop on the source
| );
|
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Parameters
pDataObject
Points to an instance of the IDataObject interface, which provides the data being dragged.
pDropSource
Points to an instance of the IDropSource interface, which is used to communicate with the source during the drag
operation.
dwOKEffect
Specifies the effects the source allows in the OLE drag and drop operation.
Most significant is whether it permits a move. The dwOKEffect and pdwEffect parameters obtain values from the DROPEFFECT enumeration. For a list of values, see DROPEFFECT.
pdwEffect
Points to a value that indicates how the OLE drag and drop operation affected
the source data. The pdwEffect parameter is set only if the operation is not canceled.
Return Values
DRAGDROP_S_DROP
Indicates the OLE drag and drop operation was successful.
DRAGDROP_S_CANCEL
Indicates the OLE drag and drop operation was canceled.
E_OUTOFMEMORY
Out of memory.
E_UNSPEC
Indicates an unexpected error occurred.
Comments
If you are developing an application that can act as a data source for an OLE
drag and drop operation, you must call DoDragDrop when you detect that the user has started an OLE drag and drop operation.
The DoDragDrop function enters a loop in which it calls various methods in the IDropSource and IDropTarget interfaces.
- The DoDragDrop function determines the window under the current cursor location. It then
checks to see if this window is a valid drop target.
- If the window is a valid drop target, DoDragDrop calls IDropTarget::DragEnter. This method returns an effect code indicating what would happen if the drop
actually occurred. For a list of valid drop effects, see the DROPEFFECT enumeration.
- DoDragDrop calls IDropSource::GiveFeedback with the effect code so that the drop source interface can provide
appropriate visual feedback to the user. The pDropSource pointer passed into DoDragDrop specifies the appropriate IDropSource interface.
- DoDragDrop tracks mouse cursor movements and changes in the keyboard or mouse button
state.
- If there is a change in the keyboard or mouse button state, DoDragDrop calls IDropSource::QueryContinueDrag and determines whether to continue the drag, to drop the data, or to cancel
the operation based on the return value.
- If the return value is S_OK, DoDragDrop first calls IDropTarget::DragOver to continue the operation. This method returns a new effect value and DoDragDrop then calls IDropSource::GiveFeedback with the new effect so appropriate visual feedback can be set. For a list of
valid drop effects, see the DROPEFFECT enumeration. IDropTarget::DragOver and IDropSource::GiveFeedback are paired so that as the mouse moves across the drop target, the user is
given the most up-to-date feedback on the mouse's position.
- If the return value is DRAGDROP_S_DROP, DoDragDrop calls IDropTarget::Drop. The DoDragDrop function returns the last effect code to the source, so the source
application can perform the appropriate operation on the source data, for example, cut
the data if the operation was a move.
- If the return value is DRAGDROP_S_CANCEL, the DoDragDrop function calls IDropTarget::DragLeave.
See Also
IDropSource::GiveFeedback
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