PRB: ChangeDisplaySettingsEx() Fails When Called From a Service (249677)

RESOLUTION

To resolve this problem, attach the currently active Desktop to the thread that is running in the service.

The code demonstrates how to do the following:

1. Switch to the active Desktop.
2. Change the display mode.
3. Switch back to the original desktop.

The following code demonstrates how to resolve this problem.

LONG ChangeDesktopDisplaySettings(LPDEVMODE lpdm)
{
    HDESK   hdeskInput;
    HDESK   hdeskCurrent;
    long    lRetVal;

    // Save the current desktop
    hdeskCurrent = GetThreadDesktop(GetCurrentThreadId());
    if (hdeskCurrent == NULL)
        return (-1);
 
    // Determine the current input desktop
    hdeskInput = OpenInputDesktop(0, FALSE, MAXIMUM_ALLOWED);
    if (hdeskInput == NULL)
        return (-1);

    // Set thread to the input desktop.
    if (!SetThreadDesktop(hdeskInput))
        return (-1);

    // Change the display settings. 
    lRetVal = ChangeDisplaySettingsEx (NULL, lpdm, NULL, CDS_GLOBAL|CDS_UPDATEREGISTRY|CDS_NORESET,NULL); 

    // Reset thread to the original desktop.
    SetThreadDesktop(hdeskCurrent);

    // Close handle to the input desktop.
    CloseDesktop(hdeskInput);

    return lRetVal;
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