title: How to set Ellipse style trigger on TabControl to highlight when DataGrids has selection
body: <p>I have an <code>Ellipse</code> in each <code>TabControl</code> header which is to highlight blue if there is any items selected in the <code>DataGrid</code> below it, otherwise it should be Transparent. At the moment I have the <code>Trigger</code> in reverse so if the <code>DataGrid</code> <code>SelectedItems.Count</code> is 0 it is Transparent, if there is someway to have the default as transparent that would be nice.</p>
  
  <p>Note: It will have multiple tabs and associated <code>DataGrids</code>.</p>
  
  <p>How can I get the <code>Style</code> <code>Trigger</code> working correctly on the <code>Ellipse</code>?</p>
  
  <p><a href="https://i.stack.imgur.com/bMTOA.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bMTOA.jpg" alt="enter image description here"></a></p>
  
  <pre><code>&lt;TabControl Name="tcGeometry" Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="2" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Margin="5" ItemsSource="{Binding GEOMETRIES}" &gt;
      &lt;TabControl.ItemTemplate&gt;
          &lt;DataTemplate&gt;
              &lt;Grid&gt;                            
                  &lt;TextBlock Text="{Binding DISPLAY_NAME}" Margin="0,0,25,0"/&gt;
                  &lt;Ellipse x:Name="SelectionIndicator"
                           Width="8" Height="8"
                           Stroke="Black"
                           Fill="Blue"
                           StrokeThickness="1"
                           HorizontalAlignment="Right"
                           VerticalAlignment="Top"&gt;
                      &lt;Ellipse.Style&gt;
                          &lt;Style TargetType="{x:Type Ellipse}"&gt;
                              &lt;Style.Triggers&gt;
                                  &lt;DataTrigger Binding="{Binding  SelectedItems.Count, ElementName=dgAudit}"  Value="0"&gt;
                                      &lt;Setter Property="Fill" Value="Transparent" /&gt;
                                  &lt;/DataTrigger&gt;
                              &lt;/Style.Triggers&gt;
                          &lt;/Style&gt;
                      &lt;/Ellipse.Style&gt;
                  &lt;/Ellipse&gt;
              &lt;/Grid&gt;
          &lt;/DataTemplate&gt;
      &lt;/TabControl.ItemTemplate&gt;
      &lt;TabControl.ContentTemplate&gt;
          &lt;DataTemplate&gt;
              &lt;Grid ShowGridLines="False"&gt;
                  &lt;DataGrid Name="dgAudit" 
                            Grid.Row="0"
                            Grid.Column="0"
                            IsReadOnly="True"
                            ItemsSource="{Binding GEOM_ASSET_OC_LIST}"
                            HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Auto"
                            AutoGenerateColumns="False"
                            HorizontalAlignment="Stretch"
                            VerticalAlignment="Stretch"
                            RowDetailsVisibilityMode="Collapsed"
                            RowHeaderWidth="30" /&gt;
              &lt;/Grid&gt;
          &lt;/DataTemplate&gt;
      &lt;/TabControl.ContentTemplate&gt;
  &lt;/TabControl&gt;
  </code></pre>