protected void AddTextValidator(IsTextValidDelegate additionalValidator)
 {
     if (IsTextValidCheckers == null || !IsTextValidCheckers.GetInvocationList().Contains(additionalValidator))
     {
         IsTextValidCheckers += additionalValidator;
     }
 }
 public BaseFilter(IsTextValidDelegate additionalValidator)
 {
     AddTextValidator(additionalValidator);
 }