用于隐藏和取消隐藏小部件的块模式

我正在尝试从互联网获取一些数据并将其显示在列表中。

以下是我的bloc code

class StudentsBloc {
  final _repository = Repository();
  final _students = BehaviorSubject<StudentModel>();

  final BehaviorSubject<bool> _showProgress = BehaviorSubject<bool>();
  final BehaviorSubject<bool> _showNoInternetViews = BehaviorSubject<bool>();

  Observable<StudentModel> get students => _students.stream;
  Observable<bool> get showProgress => _showProgress.stream;
  Observable<bool> get showNoInternetViews => _showNoInternetViews.stream;

  //FetchStudent from my Api
  fetchStudents(String disciplineId, String schoolId, String year_id,
      String lastIndex) async {
    final student = await _repository.fetchStudents(
        disciplineId, schoolId, year_id, lastIndex);
    _students.sink.add(student);
  }

  //Check to see if user has internet or not
  isNetworkAvailable(String disciplineId, String schoolId, String year_id,
      String lastIndex) async {
    checkInternetConnection().then((isAvailable) {
      if (isAvailable) {
        fetchStudents(disciplineId, schoolId, year_id, lastIndex);
      } else {
        _students.sink.addError(NO_NETWORK_AVAILABLE);
      }
    });
  }

  Function(bool) get changeVisibilityOfProgress => _showProgress.sink.add;
  Function(bool) get changeVisibilityOfNoInternetViews =>
      _showNoInternetViews.sink.add;

  dispose() {
    _students.close();
    _showProgress.close();
    _showNoInternetViews.close();
  }
}

以下是我隐藏 unide Widgets 的主要代码

Widget buildList(StudentsBloc bloc) {
    return StreamBuilder(
      stream: bloc.students,
      builder: (context, AsyncSnapshot<StudentModel> snapshot) {
        if (snapshot.hasError) {
          bloc.changeVisibilityOfProgress(false);
          bloc.changeVisibilityOfNoInternetViews(true);

          return StreamBuilder(
            stream: bloc.showNoInternetViews,
            builder: (context, snapshot) {
              bool showNoInternetView = snapshot.hasData ?? false;

              return Visibility(
                child: Center(
                  child: Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: <Widget>[
                      Text("No Network Available"),
                      RaisedButton(
                        onPressed: () {
                          fetchStudents();
                        },
                        child: Text("Retry"),
                      )
                    ],
                  ),
                ),
                visible: showNoInternetView ? true : false,
              );
            },
          );
        }

        if (snapshot.hasData) {
          bloc.changeVisibilityOfProgress(false);
          bloc.changeVisibilityOfNoInternetViews(false);

          return Refresh(
            year_id: "2",
            schoolId: "1",
            lastIndex: "0",
            disciplineId: "1",
            child: ListView.builder(
              itemBuilder: (context, int index) {
                return buildTile(
                    snapshot.data.toBuilder().data.studentData[index]);
              },
              itemCount: snapshot.data.toBuilder().data.studentData.length,
            ),
          );
        }

        if (!snapshot.hasData) {
          return StreamBuilder(
            builder: (context, snapshot) {
              bool showProgressIndicator = snapshot.data ?? false;

              return Visibility(
                child: Center(
                  child: CircularProgressIndicator(),
                ),
                visible: showProgressIndicator ? true : false,
              );
            },
            stream: bloc.showProgress,
          );
        }
      },
    );
  }

The buildList方法被调用在body of Scaffold

void fetchStudents() {
    bloc?.changeVisibilityOfNoInternetViews(false);
    bloc?.changeVisibilityOfProgress(true);
    bloc?.isNetworkAvailable("1", "1", "2", "0");
  }

假设用户打开应用程序时有互联网，那么我可以看到circularprogressindicator然后数据列表可见 但假设一开始，当应用程序打开并且用户没有互联网时，我将显示“无网络可用”文本和一个重试按钮， 现在，如果用户已连接到互联网，然后单击按钮重试，我将在几秒钟后直接看到数据列表，而不是circularprogressindicator.我无法理解为什么NoInternetviews没有隐藏并且progressindicator在显示数据列表之前单击重试按钮时显示。

我的流没有在调用重试按钮时更新。有什么注意事项吗StreamBuilder within StreamBuilder?

我尝试改变StreamBuilder按照@ivenxu 在答案中提到的顺序，但它仍然不起作用。 以下是附加代码的链接https://drive.google.com/file/d/15Z8jXw1OpwTB1CxDS8sHz8jKyHhLwJp7/view?usp=sharing https://drive.google.com/file/d/15Z8jXw1OpwTB1CxDS8sHz8jKyHhLwJp7/view?usp=sharing https://drive.google.com/open?id=1gIXV20S1o5jYRnno_NADabuIj4w163fF https://drive.google.com/open?id=1gIXV20S1o5jYRnno_NADabuIj4w163fF

在视图层中你可以使用能见度（）小部件并在从互联网加载数据时传递可见参数 true 或 false。 让我们考虑一下如何更改 bloc 中的可见变量。 的父母能见度（）小部件的流生成器()流式传输更改数据。 对于你的情况你需要一个发布主题在您的块内传输和添加新数据，以及可观察的在您的小部件上传输此数据。

让我们展示一段代码来帮助您如何实现它

该集团包含发布主题 and 可观察的流式传输和添加数据

  //this Subject allows sending data, error and done events to the listener
  final PublishSubject<bool> _progressStateSubject = new PublishSubject();

  //the listener are streaming on changes
  Observable<bool> get progressStateStream => _progressStateSubject.stream;

  //to change your progress state
  void changeProgressState({bool state}) => _progressStateSubject.sink.add(state);

在这里您可以更改进度状态

void callWebService() async {
    //when you call your func to fetch your data change your state to true
    changeProgressState(state: true);
    .
    .
    .
    if(response != null){
      //when your call is done change the state to false
      changeProgressState(state: false);
    }
  }

您的进度小部件是

// Loading Widget
  Widget _buildLoadingWidget(Bloc bloc) {
    return StreamBuilder<bool>(
        stream: bloc.progressStateStream,//streaming on changes
        builder: (context, snapshot) {
          return Visibility(
            visible: snapshot.data ?? false,//calling when data changes
            child: Center(
              child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  Text("Loading data from API...",
                      textDirection: TextDirection.ltr),
                  CircularProgressIndicator()
                ],
              ),
            ),
          );
        });
  }