title: Tooltip Visibility
body: <p>I have the following code:</p>
  
  <pre><code>&lt;DataTemplate&gt;
      &lt;!--&lt;sdk:DataGridTextColumn Binding="{Binding Description}" Header="Description" Width="205" /&gt;--&gt;
      &lt;TextBlock  Text="{Binding Description}"    Width="232"&gt;
          &lt;ToolTipService.ToolTip  &gt;   
              &lt;ToolTip Visibility="{Binding    }"&gt;
                  &lt;sdk:DataGrid AutoGenerateColumns="False" GridLinesVisibility="None" HeadersVisibility="None" Height="Auto" ItemsSource="{Binding Contains}" &gt;
                      &lt;sdk:DataGrid.Columns&gt;
                          &lt;sdk:DataGridTextColumn Binding="{Binding Code}" Header="Code" CanUserSort="False" /&gt;
                          &lt;sdk:DataGridTextColumn Binding="{Binding Description}" Header="Description" CanUserSort="False"/&gt; 
                      &lt;/sdk:DataGrid.Columns&gt;
                  &lt;/sdk:DataGrid&gt;            
              &lt;/ToolTip&gt;
          &lt;/ToolTipService.ToolTip&gt;
      &lt;/TextBlock&gt;
  &lt;/DataTemplate&gt;
  </code></pre>
  
  <p>I would like my tooltip to show, only if there are at least one row in the <code>ItemsSource="{Binding Contains}"</code></p>
  
  <p>What do I have to write in the <code>Visibility</code> property? 
  Something like </p>
  
  <pre><code>&lt;ToolTip Visibility="{Binding Contains.Length &gt; 0}"&gt;
  </code></pre>
  
  <p>But I can't figure out what the syntax should be! Any ideas?</p>