The following table shows the four possible responses available to the target when it receives a DM_DRAGOVER message. The target sends these values to the window handle specified in the DRAGINFO data structure.
┌────────────────────┬────────────────────────────────────────┐ │Message Name │Description │ ├────────────────────┼────────────────────────────────────────┤ │DOR_DROP │Sent if the objects being dragged are │ │ │acceptable. A drop does not occur unless│ │ │DOR_DROP is returned. │ ├────────────────────┼────────────────────────────────────────┤ │DOR_NODROP │Sent if the objects being dragged are │ │ │acceptable and the target supports the │ │ │current operation, but the objects │ │ │cannot be dropped on the current │ │ │location in the target window. For │ │ │example, a list box might return │ │ │DOR_NODROP if it contains objects that │ │ │can be dropped on, but the pointer is │ │ │over an object that cannot be dropped │ │ │on. │ │ │If the target response is DOR_NODROP, │ │ │the DM_DRAGOVER message continues to be │ │ │sent to the target when: │ │ │o The pointer is moved │ │ │o A keyboard key is pressed │ │ │o The pointer is moved out of │ │ │ and back into the window. │ ├────────────────────┼────────────────────────────────────────┤ │DOR_NODROPOP │Sent if the objects being dragged are │ │ │acceptable, but the target does not │ │ │support the current operation. This │ │ │response implies that the drop may be │ │ │valid if the drag operation changes. For│ │ │example, copying a file to a shredder │ │ │would not be valid, but moving a file to│ │ │a shredder would be. │ │ │Once the target has sent DOR_NODROPOP, │ │ │no further DM_DRAGOVER messages is sent │ │ │to the target until: │ │ │o A keyboard key is pressed │ │ │o The pointer is moved out of │ │ │ and back into the window. │ ├────────────────────┼────────────────────────────────────────┤ │DOR_NEVERDROP │Sent when the objects being dragged are │ │ │not acceptable, and the target will │ │ │never accept them. │ │ │Once the target has sent DOR_NEVERDROP, │ │ │no further DM_DRAGOVER messages are sent│ │ │to that target until the pointer is │ │ │moved out of and back into the target │ │ │window. │ └────────────────────┴────────────────────────────────────────┘
If a reply other than DOR_DROP is received from a target, the augmentation emphasis is automatically changed to indicate that no drop is allowed. This gives the user a visible cue that a drop cannot occur. The emphasis is reverted to drop allowed when a DOR_DROP reply is received from some target.