The WM_SETFOCUS message is sent to a window after it has gained the keyboard focus.
WM_SETFOCUS
hwndLoseFocus = (HWND) wParam; // handle to window losing focus
An application should return zero if it processes this message.
To display a caret, an application should call the appropriate caret functions when it receives the WM_SETFOCUS message.
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.
Keyboard Input Overview, Keyboard Input Messages, SetFocus, WM_KILLFOCUS