Can not disable screen from auto locking

Question

Windows Phone 8.1 Project in VS 2013.
I try the following:
using Microsoft.Phone.Shell;
PhoneApplicationService phoneAppService = PhoneApplicationService.Current;
phoneAppService.UserIdleDetectionMode = IdleDetectionMode.Disabled;
The Microsoft.Phone.dll must be referenced. No problem so far.
Compilng the Project leads to a missing System.Windows.dll Version 2.something.
Error 1 The type 'System.Windows.IApplicationService' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Windows, Version=2.0.6.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e'.
If I try to reference a System.Windows.dll VS tell me, that this dll is referenced automatically.
How can I get around this? Or is there a different way in 8.1?

Answer 1

I have it. I need to use a "Silverlight" project. I took a normal windows store app project before.
Well.... now I have to rewrite a lot of things, hope it is working. If anybody find out to do this in a normal None-Silverlight app I would be happy.
FOUND IT:
http://msdn.microsoft.com/en-us/library/windows/apps/br241816.aspx?cs-save-lang=1&cs-lang=csharp#code-snippet-1
Micha