The WM_ACTIVATEAPP message is sent when a window belonging to a different application than the active window is about to be activated. The message is sent to the application whose window is being activated and to the application whose window is being deactivated.
WM_ACTIVATEAPP
fActive = (BOOL) wParam; // activation flag
dwThreadID = (DWORD) lParam: // thread identifier
Parameters
fActive
Value of wParam. Specifies whether the window is being activated or deactivated. This parameter is TRUE if the window is being activated; it is FALSE if the window is being deactivated.
dwThreadID
Value of lParam. Specifies a thread identifier. If the fActive parameter is TRUE, dwThreadID is the identifier of the thread that owns the window being deactivated. If fActive is FALSE, dwThreadID is the identifier of the thread that owns the window being activated.
Return Values
If an application processes this message, it should return zero.
See Also