title: ListPicker not working with MVVM Light
body: <p>I am building a simple windown phone 7 Page. I'm doing MVVM (using MVVM light) and binding a <code>List&lt;Category&gt;</code> type property to <code>ListPicker</code>. This property is defined in a view model named <code>AddExpenseViewModel</code> like below</p>
  
  <pre><code>public class AddExpenseViewModel:ViewModelBase 
  {
      public List&lt;Category&gt; Categories
      {
          get { return categories; }
          set
          {
              categories = value;
              RaisePropertyChanged("Categories");
          }
      }
  }
  </code></pre>
  
  <p><code>Category</code> class is defined as </p>
  
  <pre><code>public class Category
  {
      public string Name { get; set; }
  }
  </code></pre>
  
  <p>In my XAML I first define a resource as</p>
  
  <p><code>&lt;UserControl.Resources&gt;
      &lt;bs:ViewModelLocator x:Key="ViewModelLocator" /&gt;
  &lt;/UserControl.Resources&gt;</code></p>
  
  <p>Then set the <code>DataContext</code> of the grid that contains the <code>ListPicker</code> as </p>
  
  <pre><code>&lt;Grid x:Name="ContentPanel" 
                Grid.Row="1" 
                Margin="13,1,11,-1" 
                DataContext="{Binding Path=AddExpenseViewModel, 
                                      Source={StaticResource ViewModelLocator}}"&gt;
  </code></pre>
  
  <p>And here is my XAML for <code>ListPicker</code></p>
  
  <pre><code>&lt;toolkit:ListPicker 
              HorizontalAlignment="Left" 
              Height="50" 
              Width="200" 
              Grid.Row="2" 
              Grid.Column="1" 
              DataContext="{Binding AddExpenseViewModel}"
              ItemsSource="{Binding Path=Categories, Mode=OneWay}" &gt;
              &lt;toolkit:ListPicker.ItemTemplate&gt;
                  &lt;DataTemplate&gt;
                      &lt;StackPanel Orientation="Horizontal"&gt;
                          &lt;Border Background="LightGreen" Width="*" Height="*"&gt;
                              &lt;TextBlock Text="{Binding Name}"&gt;&lt;/TextBlock&gt;
                          &lt;/Border&gt;
                      &lt;/StackPanel&gt;
                  &lt;/DataTemplate&gt;
              &lt;/toolkit:ListPicker.ItemTemplate&gt;
  &lt;/toolkit:ListPicker&gt;`
  </code></pre>
  
  <p>This does not work. The <code>ListPicker</code> is always empty. Am I doing anything wrong here?</p>