validate method

Implementation

@override
String? validate(DateTime? data) {
  if (data != null) {
    if (minTime != null && minTime!.isAfter(data)) {
      return 'Selected time is before the allowed range!';
    } else if (maxTime != null && maxTime!.isBefore(data)) {
      return 'Selected time is after the allowed range!';
    }
  } else {
    return 'Date not selected!';
  }
  return null;
}