title: WPF DataGrid trigger on other cell value
body: <p>I have <code>DataGrid</code>:</p>
  
  <pre><code>&lt;DataGrid x:Name="PART_DataGrid"
              ItemsSource="{TemplateBinding Items}"
              AutoGenerateColumns="False"
              Margin="2,25,2,2"&gt;
  &lt;DataGrid.Columns&gt;
      &lt;DataGridTemplateColumn Header="Language" Width="SizeToCells" IsReadOnly="False"&gt;
          &lt;DataGridTemplateColumn.CellTemplate&gt;
              &lt;DataTemplate&gt;
                  &lt;ComboBox SelectedItem="{Binding Path=Language, Mode=OneWay}"
                              ItemsSource="{Binding LanguagesSource, RelativeSource={RelativeSource AncestorType=UserControl}}"
                              FontSize="16"
                              IsEnabled="False"&gt;
                      &lt;ComboBox.Style&gt;
                          &lt;Style TargetType="ComboBox"&gt;
                              &lt;Style.Triggers&gt;
                                  &lt;DataTrigger Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type DataGridRow}}, Path=test }" Value=""&gt;
                                      &lt;Setter Property="IsEnabled" Value="True"/&gt;
                                  &lt;/DataTrigger&gt;
                              &lt;/Style.Triggers&gt;
                          &lt;/Style&gt;
                      &lt;/ComboBox.Style&gt;
                  &lt;/ComboBox&gt;
              &lt;/DataTemplate&gt;
          &lt;/DataGridTemplateColumn.CellTemplate&gt;
      &lt;/DataGridTemplateColumn&gt;
      &lt;DataGridTemplateColumn  Header="Translation" Width="SizeToCells" IsReadOnly="False"&gt;
          &lt;DataGridTemplateColumn.CellTemplate&gt;
              &lt;DataTemplate&gt;
                  &lt;TextBox x:Name="TranslationValueTB" 
                      Text="{Binding Path=Value, UpdateSourceTrigger=PropertyChanged}"
                              BorderThickness="0"
                              FontSize="16" /&gt;
              &lt;/DataTemplate&gt;
          &lt;/DataGridTemplateColumn.CellTemplate&gt;
      &lt;/DataGridTemplateColumn&gt;
  &lt;/DataGrid.Columns&gt;
  </code></pre>
  
  <p></p>
  
  <p>And I want to set that first column <code>ComboBox</code> will be enabled when second <code>TextBox.Text</code> is empty, I have tried different binding methods but none of them have worked. So how can I do that?</p>