It works !!!

Thanks to both,

Hi, 

So Nik's suggestion is correct then. You should use an UnboundColumn. 

All you would need to do then, is write a IValueConverter that would take the 2 dates, add them together and return them: 

 public class MVC : IValueConverter

    {

        #region IValueConverter Members

        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)

        {

            YourDataObject data = (YourDataObject)value;

            return data.FinishWorkingTime - data.StartWorkingTime;

        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)

        {

            return value;

        }
   #endregion

    }

Then place your ValueConverter in the column: 

      <ig:XamGrid.Columns>

                <ig:UnboundColumn ValueConverter="{StaticResource mvc}" Key="WorkDuration"/>

            </ig:XamGrid.Columns>

And the StaticResource is defined as: 

 <local:MVC x:Key="mvc"/>

Hope this helps, 

-SteveZ

Hi Nokolay

as i'm not an expert programmer.I try explain my problem.

The XamGrid has a DB table as ItemsSource,

In this table there are 2 columns : StartWorkingTime and FinishWorkingTime, which visibility is set to collapsed.

The third and the new column the WorkDuration is the difference beetween FinishWorkingTime and StartWorkingTime.

For example the StartWorkingTime = 14.30 and FinishWorkingTime = 15:00 the WorkDuration will be 00:30.

Thanks let me know