validate method

@override String? validate(BuildContext context, String fieldName, String? value)

Function to validate the form input. It takes a string and returns an String error message if the input is invalid or null if the input is valid.

Implementation

@override
String? validate(
  BuildContext context,
  String fieldName,
  String? value,
) {
  _longErrorMessage = null;
  _shortErrorMessage = null;

  if (value != null && value.isNotEmpty) {
    final l10n = context.l10n;

    if (!items.contains(value)) {
      _shortErrorMessage = l10n.invalidMessage;
      _longErrorMessage = l10n.invalidList;
    }
  }

  _isValid = _shortErrorMessage == null;
  return _shortErrorMessage;
}