title: Silverlight databinding to itemsource in parent's parent datacontext
body: <p>I have a datagrid where in one of the column's header I would like to have a dropdown that filters the data in the grid. The issue being that the datacontext that has the values that would be in this dropdown is in the usercontrol's viewmodel not the datagrids itemssource so the list doesn't seem to be available to the dropdown.</p>
  
  <pre><code>                &lt;sdk:DataGridTemplateColumn.HeaderStyle&gt;
                      &lt;Style TargetType="sdk:DataGridColumnHeader"&gt;
                          &lt;Setter Property="ContentTemplate"&gt;
                              &lt;Setter.Value&gt;
                                  &lt;DataTemplate&gt;
                                      &lt;StackPanel Orientation="Horizontal"&gt;
                                          &lt;TextBlock Text="Assignee" /&gt;
                                          &lt;ComboBox x:Name="cboAttorneyHdr" ItemsSource="{Binding Path=Attorneys}" 
                                                    Margin="3,0,0,0" SelectedItem="{Binding Path=SelectedAttorney, Mode=TwoWay}" /&gt;
                                      &lt;/StackPanel&gt;
                                  &lt;/DataTemplate&gt;
                              &lt;/Setter.Value&gt;
                          &lt;/Setter&gt;
                      &lt;/Style&gt;
                  &lt;/sdk:DataGridTemplateColumn.HeaderStyle&gt;
  </code></pre>
  
  <p>I found an example using relative source for WPF that seems to be asking the same thing but it seems that this doesn't work for Silverlight.  I have tried setting this manually in the code behind but the combobox does appear to be available there either!</p>