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.
A window receives this message through its WindowProc function.
Indicates 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.
The thread identifier. If the wParam parameter is TRUE, lParam is the identifier of the thread that owns the window being deactivated. If wParam is FALSE, lParam is the identifier of the thread that owns the window being activated.
If an application processes this message, it should return zero.
Minimum supported client
|Windows 2000 Professional [desktop apps only]|
Minimum supported server
|Windows 2000 Server [desktop apps only]|
Build date: 11/16/2013