validate method

@override String? validate(dynamic value)

Return an error message if the value is invalid, otherwise return null.

Implementation

@override
String? validate(dynamic value) {
  if(minChars > 0 && value.length < minChars ) {
    return "$value must be at least $minChars characters long.";
  }
  if(maxChars > 0 && value.length > maxChars) {
    return "$value must be at most $maxChars characters long.";
  }
  if(hasOption(optionLowercase)) {
    if(value.toLowerCase() != value) {
      return "$value must be all lowercase";
    }
  }
  return null;
}