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?

Put this in your window constructor

WindowStartupLocation = System.Windows.WindowStartupLocation.CenterScreen;

.NET FrameworkSupported in: 4, 3.5, 3.0

.NET Framework Client ProfileSupported in: 4, 3.5 SP1

xaml

<Window ... WindowStartupLocation="CenterScreen">...