Problem setting the custom cell validation.

[SivaPrasad Bevara]

Hi,

I am using Telerik controls for Silverlight 5.

I need to set the Unique key validation for a cell.

On the "CellValidating" event, I am sending the cell value to the database and checking the value.

Here the problem is with the asyncronous Domain service.

I am using the MVVM architecture and Domain service. I have implemented the "CellValidating" event in the view model and in that event I am calling the service method as below.

public void CellUniqueValidation(object obj)
        {

            GridViewCellValidatingEventArgs e = (GridViewCellValidatingEventArgs)((Emps.ExtendedCommandParameter)(obj)).EventArgs;
            var currentColumn = e.Cell.Column as IDataGridColumn; //pointer to the cell's column

            if ((currentColumn != null)) //both are present
            {
                var newData = e.NewValue == null ? "" : (e.NewValue).ToString(); //get the new value
                var oldData = e.OldValue == null ? "" : (e.OldValue).ToString(); //get the old value

                    if (currentColumn.GridColumnIsUnique && newData != "")
                    {
                        //CheckUniqueness

                        _context.CheckUniqueness("Employee", "emp_id", operation =>
                        {
                           operation.Completed += new EventHandler(Uniqueness_operation_Completed);
                        }, null);

                        //e.ErrorMessage = "This is unique"; //set the error massage
                        //e.IsValid = false;
                        //return;
                    }
              }

        }

And the opearation completed method is as below:

void Uniqueness_operation_Completed(object sender, EventArgs e)
       {
           if (((System.ServiceModel.DomainServices.Client.InvokeOperation<bool>)(sender)) != null)
           {
               if (((System.ServiceModel.DomainServices.Client.InvokeOperation<bool>)(sender)).Value)
               {
                  //We can get the value here
               }
           }
       }

Here the problem is, we can know whether it is unique or not in the opration completed event,
but there I cant set the error message as I cant access that cell there.
 
How can I set the error message to that cell in the operation completed event.
Or is there any way I can get the value from the domain service, in the CellValidating event itself.

FYI: I am returning a scalar value from the domain service.

Please help.

Regards,
SivaPrasad.B