title: Windows store app, How to get the header value of gridview?
body: <p>Here is the groupstyle of gridview in .xaml.</p>
  
  <pre><code>        &lt;GridView.GroupStyle&gt;
              &lt;GroupStyle&gt;
                  &lt;GroupStyle.HeaderTemplate&gt;
                      &lt;DataTemplate&gt;
                          &lt;Button x:Name="HeaderBtn" Click="HeaderButton_Click"&gt;
                              &lt;StackPanel Orientation="Horizontal"&gt;
                                  &lt;TextBlock x:Name="Title" Text="{Binding Key}" /&gt;
                                  &lt;TextBlock Text="{StaticResource ChevronGlyph}" /&gt;
                              &lt;/StackPanel&gt;
                          &lt;/Button&gt;
                      &lt;/DataTemplate&gt;
                  &lt;/GroupStyle.HeaderTemplate&gt;
               &lt;/GourpStyle&gt;
          &lt;/GridView.GroupStyle&gt;
  </code></pre>
  
  <p>The binding value key is the key of list.</p>
  
  <p>Here is the button action.</p>
  
  <pre><code>    private void HeaderButton_Click(object sender, RoutedEventArgs e)
      {
  
      }
  </code></pre>
  
  <p>When I click the button, how I get the text value of text block whose x:Name is "Title"?</p>