An application sends a CB_SHOWDROPDOWN message to show or hide the list box of a combo box that has the CBS_DROPDOWN or CBS_DROPDOWNLIST style.
CB_SHOWDROPDOWN
wParam = (WPARAM) (BOOL) fShow; // the show/hide flag
lParam = 0; // not used; must be zero
The return value is always TRUE.
This message has no effect on a combo box created with the CBS_SIMPLE style.
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_GETDROPPEDSTATE