The WM_QUERYOPEN message is sent to an icon when the user requests that the window be restored to its previous size and position.
WM_QUERYOPEN
This message has no parameters.
If the icon can be opened, an application that processes this message should return TRUE; otherwise, it should return FALSE to prevent the icon from being opened.
The DefWindowProc function returns TRUE.
While processing this message, the application should not perform any action that would cause an activation or focus change (for example, creating a dialog box).