title: wpf datagrid expander show x items
body: <p>I have an <code>Expander</code> in my <code>DataGrid</code>, but I want to only show TWO items, and then when user click on expand, show remaining items.</p>
  
  <p>How can that be done ?</p>
  
  <pre><code>&lt;DataGrid.GroupStyle&gt;
      &lt;GroupStyle AlternationCount="7" &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 IsExpanded="False" Background="{Binding XPath=recipient_color}"&gt;                                            
                                  &lt;Expander.Header&gt;
                                      &lt;Label Content="{Binding}"&gt;
                                      &lt;/Label&gt;                                                
                                  &lt;/Expander.Header&gt;
                                  &lt;Expander.Content&gt;
                                      &lt;ItemsPresenter/&gt;
                                  &lt;/Expander.Content&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>