Question

我正在尝试从互联网上获取一些数据并将其显示为列表。

以下是我的bloc代码

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();
  }
}

以下是我隐藏统一控件的主要代码

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,
          );
        }
      },
    );
  }

在buildList的{{1}}中调用body方法

Scaffold

假设打开应用程序时用户可以上网，那么我可以看到void fetchStudents() { bloc?.changeVisibilityOfNoInternetViews(false); bloc?.changeVisibilityOfProgress(true); bloc?.isNetworkAvailable("1", "1", "2", "0"); }，然后可以看到数据列表但假设开始时打开应用程序且用户没有互联网，那么我会显示“无网络可用文本”和一个重试按钮，现在，如果用户已连接到Internet，然后单击按钮重试，则几秒钟后我将直接看到数据列表，而不是circularprogressindicator。我无法理解为什么circularprogressindicator是在显示数据列表之前单击重试按钮，则不会隐藏并且显示NoInternetviews。

我的流在调用的重试按钮上没有得到更新。 progressindicator中有关于StreamBuilder的警告吗？

我尝试更改答案中的StreamBuilder，如@ivenxu所述，但仍然无法正常工作。以下是附加代码的链接 https://drive.google.com/file/d/15Z8jXw1OpwTB1CxDS8sHz8jKyHhLwJp7/view?usp=sharing https://drive.google.com/open?id=1gIXV20S1o5jYRnno_NADabuIj4w163fF

Answer 1

在视图层中，可以使用 Visibility（）小部件并在从Internet加载数据时传递可见参数true或false。让我们考虑一下如何从bloc更改可见变量。 Visibility（）的父级使用 StreamBuilder（）小部件以流式传输更改数据。对于您的情况，您需要在您的Bloc内部使用 PublishSubject 来流式传输和添加新数据，并且需要 Observable 来在小部件上流式传输这些数据。

让我们显示一个片段代码以帮助您如何实现它

该集团包含 PublishSubject 和 Observable 以便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);

您可以在此处更改进度状态

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()
                ],
              ),
            ),
          );
        });
  }

Answer 2

原因似乎是CircularProgressIndicator位于学生流的更新周期之内。在重试的情况下，当从网络电话返回数据时，学生只会获得下一个快照。

尝试更改流构建器的顺序，尝试将学生流构建器放入进度流构建器中。

Widget buildList(StudentsBloc bloc) {
    return StreamBuilder(
      stream: bloc.showProgress,
      builder: (context, snapshot) {
        bool showProgressIndicator = snapshot.data ?? false;
        if (!showProgressIndicator) {
             StreamBuilder(
            stream: bloc.students,
            builder: (context, AsyncSnapshot<StudentModel> snapshot) {
               ....
               //your original code without progress StreamBuilder
            }
        }
        return Visibility(
        child: Center(
            child: CircularProgressIndicator(),
        ),
        visible: showProgressIndicator ? true : false,
        );
    },

    );
  }

Bloc Pattern隐藏和取消隐藏小部件

2 个答案: