flutter - 流订阅不监听flutter的变化

Question

我正在尝试以BLoC模式获取Firestore文档。有两个事件，一个获取所有文档，另一个根据查询获取文档。这是两个事件的代码：

  Stream<JobFeedState> _mapFetchAllJobPostsToState(
      FetchAllJobPosts event) async* {
    yield LoadingJobPosts();
    try {
      _jobsSubscription?.cancel();
      _jobsSubscription = _jobsRepository.getAllTheJobsPosted().listen((jobs) {
        add(JobPostsRefreshed(jobs: jobs));
      });
    } catch (e) {
      yield Error(message: e.toString());
    }
  }

  Stream<JobFeedState> _mapFetchJobPostsForLocation(
      FetchJobPostsForLocation event) async* {
    yield LoadingJobPosts();
    try {
      _jobsSubscription?.cancel();
      _jobsInLocationsubscription?.cancel();
      _jobsInLocationsubscription =
          _jobsRepository.getJobsInALocation(event.location.country).listen((jobs) {
        add(JobPostsRefreshed(jobs: jobs));
      });
    } catch (e) {
      yield Error(message: e.toString());
    }
  }

_mapFetchAllJobPostsToState()正在按预期工作。但另一个，_mapFetchJobPostsForLocation()第一次获取数据，但它没有显示流中的变化。这是基于查询获取数据的函数：

  // getJobsInALocation()
  Stream<List<JobPostDocumentModel>> getJobsInALocation(String location) {
    var collectionGroup =
        Firestore.instance.collectionGroup(AppStringConstants.posts);
    return collectionGroup
        .where(AppStringConstants.country, isEqualTo: location)
        .snapshots()
        .map((snapshot) {
      return snapshot.documents.map((docSnapshot) {
        DocumentReference documentReference = docSnapshot.reference;
        JobPostModel jobPostModel = JobPostModel.fromSnapshot(docSnapshot);
        JobPostDocumentModel jobPostDocumentModel = JobPostDocumentModel(
          documentReference: documentReference,
          jobPostModel: jobPostModel,
        );
        return jobPostDocumentModel;
      }).toList();
    });
  }

这里有什么问题？