validator method

@override UsernameError? validator(String value)

A function that must return a validation error if the provided value is invalid and null otherwise.

Implementation

@override
UsernameError? validator(String value) {
  final trimmed = value.trim();
  if (trimmed.isEmpty) return UsernameError.empty;
  if (trimmed.length < minLength) return UsernameError.tooShort;
  if (maxLength != null && trimmed.length > maxLength!) {
    return UsernameError.tooLong;
  }

  return null;
}