Enabling/Disabling Aero from a Windows Service
- by rgould
I have some code to enable/disable the Windows Aero service in Vista, and I would like to run it in a Windows Service. The code works in a standalone application, but when I run it from a Service, nothing happens. No errors or exceptions are thrown.
I realise that running code in a service is a different scope than running code in an application, but in this case, how would I enable/disable Aero from the service? Is this even possible?
Here is the code I am working with:
public static readonly uint DWM_EC_DISABLECOMPOSITION = 0;
public static readonly uint DWM_EC_ENABLECOMPOSITION = 1;
[DllImport("dwmapi.dll", EntryPoint="DwmEnableComposition")]
protected static extern uint Win32DwmEnableComposition(uint uCompositionAction);
public static bool EnableAero()
{
Win32DwmEnableComposition(DWM_EC_ENABLECOMPOSITION);
}
Edit:
It turns out that the DwmEnableComposition call is returning HRESULT 0x80070018, or ERROR_BAD_LENGTH. Seems like a strange error, since the code works when not running as a service.
I also tried changing the entire thing to the following code, but got the same result. It sets the window station and desktop, and it seems to be correct, but the call to DwmEnableComposition results in the same error. I've not included the PInvoke declarations for brevity.
protected override void OnStop()
{
IntPtr winStation = OpenWindowStation("winsta0", true, 0x10000000 /* GENERIC_ALL */);
if (winStation == null || winStation.ToInt32() == 0)
{
String err = new Win32Exception(Marshal.GetLastWin32Error()).Message;
}
if (!SetProcessWindowStation(winStation))
{
String err = new Win32Exception(Marshal.GetLastWin32Error()).Message;
}
uint thread = GetCurrentThreadId();
IntPtr hdesk = OpenInputDesktop(0, false, 0x10000000 /* GENERIC_ALL */);
if (hdesk == null || hdesk.ToInt32() == 0)
{
String err = new Win32Exception(Marshal.GetLastWin32Error()).Message;
}
if (!SetThreadDesktop(hdesk))
{
String err = new Win32Exception(Marshal.GetLastWin32Error()).Message;
}
uint result = Win32DwmEnableComposition(DWM_EC_DISABLECOMPOSITION);
if (result != 0)
{
String err = new Win32Exception(Marshal.GetLastWin32Error()).Message;
}
}
