An application sends the LBN_SETFOCUS notification message when a list box receives the keyboard focus. The parent window of the list box receives this notification message through the WM_COMMAND message.
LBN_SETFOCUS
idListBox = (int) LOWORD(wParam); // identifier of list box
hwndListBox = (HWND) lParam; // handle to list box
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Requires version 1.0 or later.
Header: Declared in winuser.h.
List Boxes Overview, List Box Messages, LBN_KILLFOCUS, WM_COMMAND