title: WPF Datagrid group expander text - how to bind?
body: <p>I am using a datagrid with a combox that should change the grouping field. I am using the following xaml to define the general grouping template : </p>
  
  <pre><code>&lt;DataGrid.GroupStyle&gt;
          &lt;GroupStyle&gt;
              &lt;GroupStyle.ContainerStyle&gt;
                  &lt;Style TargetType="{x:Type GroupItem}"&gt;
                      &lt;Setter Property="Template"&gt;
                          &lt;Setter.Value&gt;
                              &lt;ControlTemplate TargetType="{x:Type GroupItem}"&gt;
                                  &lt;Expander&gt;
                                      &lt;Expander.Header&gt;
                                          &lt;StackPanel Orientation="Horizontal"&gt;
                                              &lt;TextBlock Text="NEEDS TO BE BINDED..."/&gt;
                                          &lt;/StackPanel&gt;
                                      &lt;/Expander.Header&gt;
                                      &lt;ItemsPresenter /&gt;
                                  &lt;/Expander&gt;
                              &lt;/ControlTemplate&gt;
                          &lt;/Setter.Value&gt;
                      &lt;/Setter&gt;
                  &lt;/Style&gt;
              &lt;/GroupStyle.ContainerStyle&gt;
          &lt;/GroupStyle&gt;
      &lt;/DataGrid.GroupStyle&gt;
  </code></pre>
  
  <p>I only need to be able to 'reach' that TextBlock within the expander to be able to output the selected grouping applied.</p>
  
  <p>Please help....</p>