An application sends a CB_SETEXTENDEDUI message to select either the default user interface or the extended user interface for a combo box that has the CBS_DROPDOWN or CBS_DROPDOWNLIST style.
CB_SETEXTENDEDUI
wParam = (WPARAM) (BOOL) fExtended; // extended user interface flag
lParam = 0; // not used; must be zero
If the operation succeeds, the return value is CB_OKAY. If an error occurs, it is CB_ERR.
By default, the f4 key opens or closes the list and the down arrow changes the current selection. In the extended user interface, the f4 key is disabled and the down arrow key opens the drop-down list.
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.
Combo Boxes Overview, Combo Box Messages, CB_GETEXTENDEDUI