title: Display custom width tooltip in WPF DataGrid
body: <p>I am displaying a tooltip in a WPF DataGrid but I want to customize the width of it so it is no larger then the size of the cell containing the data.  I tried setting the Path to "Width" and "ActualWidth" but it ignores them both.  What am I doing wrong?</p>
  
  <pre><code>&lt;DataGridTextColumn Binding="{Binding Description}" Header="Message" Width="*"&gt;
  &lt;DataGridTextColumn.ElementStyle&gt;
      &lt;Style TargetType="{x:Type TextBlock}"&gt;
          &lt;Setter Property="TextTrimming" Value="CharacterEllipsis" /&gt;
          &lt;Style.Triggers&gt;
              &lt;Trigger Property="IsMouseOver" Value="True"&gt;
                  &lt;Setter Property="ToolTipService.ShowDuration" Value="60000" /&gt;
                  &lt;Setter Property="ToolTip"&gt;
                      &lt;Setter.Value&gt;
                          &lt;TextBlock TextWrapping="Wrap"
                              Width="{Binding RelativeSource={RelativeSource AncestorType=DataGridCell}, Path=ActualWidth}"
                              Text="{Binding Description}" /&gt;
                      &lt;/Setter.Value&gt;
                  &lt;/Setter&gt;
              &lt;/Trigger&gt;
          &lt;/Style.Triggers&gt;
      &lt;/Style&gt;
  &lt;/DataGridTextColumn.ElementStyle&gt;
  &lt;/DataGridTextColumn&gt;
  </code></pre>