The WM_SHOWWINDOW message is not sent under the following circumstances:
When a top-level, overlapped window is created with the WS_MAXIMIZE or WS_MINIMIZE style.
When the SW_SHOWNORMAL flag is specified in the call to the ShowWindow function.
SW_SHOWMAXIMIZED
Activates the window and displays it as a maximized window.
SW_SHOWNORMAL
Activates and displays a window. If the window is minimized or maximized, the system restores it to its original size and position. An application should specify this flag when displaying the window for the first time.