App.xml

<?xml version="1.0" encoding="utf-8"?>
<Application x:Class="KhanAcademyWp8.App" 
..... 
              xmlns:viewModel2="clr-namespace:KhanAcademyWp8.ViewModel"
             mc:Ignorable="d" >
<Application.Resources>
        
                    <viewModel2:ViewModelLocator x:Key="Locator" d:IsDataSource="True" />
     ...          
</Application.Resources>
  
  ...
</Application>