The container control sends a WM_CONTROL (in Container Controls) message with the CN_PICKUP notification code to its owner when a pickup and drop operation is initiated over a container.
param1
USHORT id /* Container control ID. */
USHORT CN_PICKUP /* Notification code. */
param2
PCNRDRAGINIT pCnrDragInit /* Pointer to the CNRDRAGINIT structure containing direct-manipulation information initiatedin a container. */
returns
ULONG ulReserved /* Reserved value, must be 0. */