为什么在Flutter中向Sink添加数据不起作用？

Question

目的非常简单。在获取数据后，可以通过特定的一组字符串进行过滤。因此，我最初使用“all”进行过滤，这意味着显示所有数据，并且当点击任何选择芯片时，基于该特定字符串进行过滤。除了从api调用中加载数据后不显示所有数据外，一切都正常工作。即使我再次热重载，也会显示完整的列表数据。因此，基本上将字符串数据添加到Sink中不起作用。我认为我犯了一些愚蠢的错误，但无法找出。需要建议。

BLOC类

final Application _application;

ProductListScreenBloc(this._application);
int totalPages = 1;


final _productList = BehaviorSubject<List<Product>>();
Observable<List<Product>> _filteredProductList = Observable.empty();
final _filterName = BehaviorSubject<String>();


Stream<List<Product>> get productList => _productList.stream;
Stream<List<Product>> get filteredProductList => _filteredProductList;
Sink<String> get filterName => _filterName;


void loadBrandWiseProductList(
  String categorySlug, String brandSlug, int pageNo) {

if (totalPages >= pageNo) { //for pagination

  StreamSubscription subscription = _application.productListRepository
      .getBrandWiseProductList(categorySlug, brandSlug, pageNo)
      .listen((ProductListResponse response) {
    if (_productList.value == null) {

      totalPages = response.totalPage;
      _productList.add(response.productList);

      filterName.add('all');

      _filteredProductList = Observable.combineLatest2(
              _filterName, _productList, applyModelFilter)
          .asBroadcastStream();
    } 
  });

  }
 }

List<Product> applyModelFilter(
String filter,
List<Product> products,
) {
if (filter == 'all') {
  return products;
} else {
  return products
      .where((seriesSLug) => seriesSLug.series.slug == filter)
      .toList();
 }
}

用户界面部件类

 class _AllSeriesModelListScreenState extends State<AllSeriesModelListScreen> {
 AllSeriesModelListScreenArguments allSeriesModelListScreenArguments;

 ProductListScreenBloc bloc;

 int _selectedSeriesChipValue = -1;
 int _pageNo = 1;

 @override
 void initState() {
 super.initState();
 }

 @override
 void dispose() {
 super.dispose();
 bloc.dispose();
}

@override
Widget build(BuildContext context) {
RouteSettings settings = ModalRoute.of(context).settings;
allSeriesModelListScreenArguments = settings.arguments;

_init();

return Scaffold(
  body: CustomScrollView(
    slivers: <Widget>[
      StreamBuilder(
          stream: bloc.filteredProductList,
          builder: (context, snapshot) {
            if (snapshot.hasData) {
              List<Product> productList = snapshot.data;

              return SliverPadding(
                padding: EdgeInsets.symmetric(
                  vertical: 8.0,
                  horizontal: 10.0,
                ),
                sliver: SliverGrid(
                  gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
                    crossAxisCount: 3,
                    crossAxisSpacing: 0.0,
                    mainAxisSpacing: 8.0,
                  ),
                  delegate: SliverChildListDelegate(
                    buildModelGridList(productList),
                  ),
                ),
              );
            } else {
              return SliverList(
                delegate: SliverChildListDelegate([
                  PaddingWithTitle(
                    title: 'No Model Available',
                  ),
                ]),
              );
            }
          })
    ],
  ),
 );
}

void _init() {
 if (null == bloc) {
  bloc = ProductListScreenBloc(
    AppProvider.getApplication(context),
  );

  bloc.loadBrandWiseProductList(
      allSeriesModelListScreenArguments.categorySlug,
      allSeriesModelListScreenArguments.brandSlug,
      _pageNo);

   }
  }
}

- demo_Ashif

Answer 1

我相信你在这两行代码中漏掉了一些东西。

final _filterName = BehaviorSubject<String>();
Sink<String> get filterName => _filterName;

你没有暴露出这个“sink”。BehaviorSubject 只是一个带有默认值和缓存最后一个值的 StreamController。所以像每个 StreamController 一样，它有两个属性 - sink 和 stream。要推送数据，您需要访问 sink。 为此，您需要键入

StreamSink<String> get filterName => _filterName.sink;

为什么您的 behavior subject 没有种子值？需要有那个“默认”值。

final _filterName = BehaviorSubject<String>(seedValue: '');

- ZlatiP

---

我已经尝试过使用种子值/不使用种子值。还更改了汇集选项。但它第一次运行就无法正常工作。否则，通过选择芯片进行过滤工作正常。即使我只是热重载，它也会显示数据。所以我认为我在监听/广播可观察对象方面做错了什么。但是我无法找出问题所在。 - demo_Ashif

Answer 2

刚刚不得不将代码更改为这样

void loadBrandWiseProductList(
String categorySlug, String brandSlug, int pageNo) {

if (totalPages >= pageNo) { //for pagination

StreamSubscription subscription = _application.productListRepository
  .getBrandWiseProductList(categorySlug, brandSlug, pageNo)
  .listen((ProductListResponse response) {
if (_productList.value == null) {

  totalPages = response.totalPage;
  _productList.add(response.productList);

} 
_filteredProductList = Observable.combineLatest2(
          _filterName, _productList, applyModelFilter)
      .asBroadcastStream();
  });

 }
}

- demo_Ashif