When a target object is dragged over by the mouse, it will always receive a wpDragOver instance method call. Many target objects will choose to decide the current drag operation and whether a drop is possible based upon their own rules. For instance, the WPShredder object will return DO_DROP,DO_MOVE if it decides that all the source objects can be deleted. However, some targets require the source or sources to participate in the decision over whether they can accept the drop. The way that a target allows a source object to have a say in what the drop action will be is by calling the wpDraggedOverObject on each source object. The wpDraggedOverObject instance method may be invoked, on an object that is being dragged (source object) at any time, to see if it can support a drop on the current target. If the object that is being dragged responds favorably to this method, it may later receive a wpDroppedOnObject instance method call so that it can process the drop action.
As an example, consider the case where a program object is dragged onto a data file object. The program would respond DO_DROP to the wpDraggedOverObject instance method, so that the data file would be a valid drop target. If the user chose to allow the drop, then the program would receive a wpDroppedOnObject instance method. Then the program would be able to open itself as a viewer of the data file object.
This method is called as a result of a DM_DRAGOVER message being sent. For further documentation of the possible return values, see DM_DRAGOVER in the Presentation Manager Programming Reference.