The WM_KILLFOCUS message is sent to a window immediately before it loses the keyboard focus.
WM_KILLFOCUS
hwndGetFocus = (HWND) wParam; // handle of window receiving focus
Parameters
hwndGetFocus
Value of wParam. Identifies the window that receives the keyboard focus (may be NULL).
Return Values
An application should return zero if it processes this message.
Remarks
If an application is displaying a caret, the caret should be destroyed at this point.
See Also