BLoC模式波动中的周期性流

Question

我正在开发一个简单的聊天应用程序，并且必须以特定的时间间隔检查API。

但是在我的BLOC逻辑中，我使用了 Observable

那么我该如何更改代码以使此流变为周期性？

final bloc = ConversationBloc();

class ConversationBloc {
  final repository = Repository();
  final conversationFetcher = PublishSubject<ConversationModel>();
  final conversationFetcherStatus = PublishSubject<MessageModel>();

  Observable<ConversationModel> get userConversation =>
      conversationFetcher.stream;

  dispose() async {
    await conversationFetcher.drain();
    conversationFetcher.close();
    conversationFetcherStatus.close();
  }

  fetchUserConversation(toUsernameController) async {
    ConversationModel conversationModel =
        await repository.fetchUserConversation(toUsernameController);
    conversationFetcher.sink.add(conversationModel);
  }

  saveConversation(Data conversation) async {
    try {
      MessageModel conversationModel =
          await repository.saveConversation(conversation);
      conversationFetcherStatus.sink.add(conversationModel);
    } catch (e) {
      conversationFetcherStatus.sink.addError(e);
    }
  }

   fetchUserConversationList(int toUsernameController) async {
    ConversationModel conversationModel =
        await repository.fetchUserConversationList(toUsernameController);
    conversationFetcher.sink.add(conversationModel);
  }
}