intro-to-flutter-22.dart

class CreateThreadBloc extends BlocBase {
  /// Title of the conversation
  Stream<String> get title => _title.transform(emptyValidationTransformer);
  final BehaviorSubject<String> _title = BehaviorSubject.seeded('');

  /// Creates new message thread or updates existing one.
  Future<Either<Exception, MessageThread>> submit() async {
    Either<Exception, MessageThread> result;
    if (initialThread == null) {
      result = await _createThread();
    } else {
      result = await _updateThread();
    }
    return result;
  }
}