validate method

@override String? validate()

Validate the value Return null if the value is valid Return the error message if the value is invalid Return null if the value is empty

Implementation

@override
String? validate() {
  DateTime? dateTime = DateTime.tryParse(_value ?? '');

  if (_value == null || _value?.trim().isEmpty == true || dateTime == null) {
    return null;
  } else if (dateTime.compareTo(min) < 0) {
    return message + ' ' + min.toString();
  } else {
    return null;
  }
}