The ItemsSource of my Grid is a IEnumerable<SampleObject>.

The SampleObject consist of Guid id, String str1, String str2 and a ObservableCollection<SampleDynObject> dy.

The SampleDynObject consist of one strTest property.

After the creation of the xamWebGrid, I create TextColumns for the id, str1 and str2 data.

For the data from the SampleDynObject, I create UnboundColumns 

UnboundColumn col = new UnboundColumn() { Key = Guid.NewGuid().ToString(), ValueConverter = new SampleConverter(), ValueConverterParameter = i }; 

The SampleConverter looks like this:

    public class SampleConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            SampleObject so  = value as SampleObject;
            int index = Int32.Parse(parameter.ToString()); //This is the index of the SampleObject's child collection
            if (so != null)
            {
                return so.dy[index].strTest;
            }
            return null;
        }
 
        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

The question is: I tried to use the ContainingConditionalFormatRule, but it worked only on the TextColumns and not on the UnboundColumns.

My idea was to manually check the Rule by adding a second ValueConverter, but it seems to be only possible in the XAML-Markup and not by code.

So, how can I format the Background of the Cells.