How to center a WPF app on screen?
You can still use the Screen class from a WPF app. You just need to reference the System.Windows.Forms assembly from your application. Once you've done that, (and referenced System.Drawing for the example below):
Rectangle workingArea = System.Windows.Forms.Screen.PrimaryScreen.WorkingArea;...works just fine.
Have you considered setting your main window property WindowStartupLocation to CenterScreen?