title: DataGridCell change if number positive or negative
body: <p>i have a DataGridTextColumn that accepts numbers from a database table called Numbers. If the number in cell is positive than i want the next DataGridTextColumn to have the word "Positive" inside. I tried with IConverter Styles but still dont know how to do it right.I hope someone can help me.</p>
  
  <p>This is my code so far: </p>
  
  <pre><code>&lt;DataGrid Grid.Row="0" Grid.Column="1" AutoGenerateColumns="False" IsReadOnly="false" CanUserAddRows="True" Margin="5,5,10,5" ItemsSource="{Binding ElementName=Numbers}"&gt;
  
          &lt;DataGrid.Columns&gt;
              &lt;DataGridTextColumn Binding="{Binding Num}" Header="Number" FontSize="16"/&gt;
  
              &lt;DataGridTextColumn Header="Positive/Negative" FontSize="16"&gt;
  
                  &lt;DataGridTextColumn.ElementStyle&gt;
                      &lt;Style TargetType="{x:Type TextBlock}"&gt;
                          &lt;Setter Property="Text" Value="{Binding Amount, Converter={StaticResource PositiveNegativeConverter}}"/&gt;
                      &lt;/Style&gt;
                  &lt;/DataGridTextColumn.ElementStyle&gt;
              &lt;/DataGridTextColumn&gt;
      &lt;/DataGrid&gt;
  </code></pre>
  
  <p>I also have this inside Resources:
     </p>
  
  <pre><code>    &lt;local:PositiveNegativeConverter x:Key="PositiveNegativeConverter"/&gt;
  &lt;/UserControl.Resources&gt;      
  </code></pre>
  
  <p>My Converter looks like this:</p>
  
  <pre><code>class PositiveNegativeConverter : IValueConverter
  {
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
      {
          bool revert = (parameter as string).StartsWith("-");
  
          string stringValue = value as string;
          string compareValue = parameter as string;
  
          if (revert)
          {
              return "Negative";
          }
          else
              return "Positive";
      }
      public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
      {
          throw new NotSupportedException();
      }
  }
  </code></pre>