The TVN_BEGINDRAG notification message notifies a tree-view control’s parent window that a drag-and-drop operation involving the left mouse button is being initiated. This notification message is sent in the form of a WM_NOTIFY message.
TVN_BEGINDRAG pnmtv = (NM_TREEVIEW FAR *) lParam
No return value.
A tree-view control that has the TVS_DISABLEDRAGDROP style does not send this notification message.