Row validation is performed within the GridControl.ValidateRow event handler, when a row is about to lose focus. The InvalidRowException event allows you to override the default error presentation. This event occurs after the GridControl.ValidateRow event (provided that the focused row's validation has failed).
Use the event parameter's InvalidRowExceptionEventArgs.ExceptionMode property to specify the action performed in response to entering an invalid value. You can display a message box with an error description, suppress any action, throw an exception or discard new data and revert to an old value.