can't view the Designer Preview on my Visual Studio 2012 Ultimate

Aug 8, 2013 at 9:14 AM
Hello There.
It's been few days that I've been using Modern UI for WPF. It's a great transition there's only one problem that I am facing.
I can't view the design preview of my gui that I am trying to work on, it's only when I run the program can see what I have done with the GUI.
Can someone help me out on this ?
Thank you.