Occurs when the object represented by the ListView's focused row must be validated.
Handle this event to perform custom validation of the objects represented by an editable List View. The object that is being validated can be accessed via the handler's Object parameter. Check whether it is valid, and if it is not, set the ValidateObjectEventArgs.Valid to false and the ValidateObjectEventArgs.ErrorText to the message that must be displayed in a UI. In this instance, it will be impossible to change the focused row until the entered data is corrected.