TVTDataObject.CanonicalI Method

Helper method for setting data in the IDataObject.

function CanonicalIUnknown(TestUnknown: IUnknown): IUnknown;

In SetData the class can get a circular reference if the client calls GetData then calls SetData with the same StgMedium. Because the unkForRelease for the IDataObject can be marshalled it is necessary to get pointers that can be correctly compared. CanonicalIUknown uses COM object identity for this task. An explicit call to the IUnknown::QueryInterface method, requesting the IUnknown interface, will always return the same pointer. See the IDragSourceHelper article by Raymond Chen at MSDN.

TVTDataObject Class