bool _validate([Set<FormFieldState<Object?>>? invalidFields]) {
    bool hasError = false;
    String errorMessage = '';
    for (final FormFieldState<dynamic> field in _fields) {
      final bool isFieldValid = field.validate();
      hasError = !isFieldValid || hasError;
      errorMessage += field.errorText ?? '';
      if (invalidFields != null && !isFieldValid) {
        invalidFields.add(field);
      }
    }

    if (errorMessage.isNotEmpty) {
      final TextDirection directionality = Directionality.of(context);
      if (defaultTargetPlatform == TargetPlatform.iOS) {
        unawaited(Future<void>(() async {
          await Future<void>.delayed(_kIOSAnnouncementDelayDuration);
          SemanticsService.announce(errorMessage, directionality,
              assertiveness: Assertiveness.assertive);
        }));
      } else {
        SemanticsService.announce(errorMessage, directionality,
            assertiveness: Assertiveness.assertive);
      }
    }
    return !hasError;
  }