The TBN_BEGINDRAG notification message notifies a toolbar’s parent window that
the user has begun dragging a button in a toolbar. This message is sent in the
form of a WM_NOTIFY message.
TBN_BEGINDRAG
ptbn = (TBNOTIFY FAR *) lParam;
Parameters
ptbn
Pointer to a TBNOTIFY structure. The iItem member contains the
zero-based index of the button being dragged.