在flutter_bloc中调用异步事件

Question

我正试图在颤振应用程序加载后立即从API中获取数据，但我无法做到这一点。

class MarketBloc extends Bloc<MarketListEvent, MarketListState> {
  MarketBloc() : super(MarketLoading()) {
    on<MarketSelectEvent>((event, emit) async {
      emit(MarketLoading());
      final data = await ApiCall().getData(event.value!);
      globalData = data;
      emit(MarketDataFetched(marDat: globalData.data, dealType: event.value));
    });

    
  }
}

我将MarketLoading状态称为初始状态，然后调用MarketSelectEvent，但在当前代码中，操作是必需的，并且我希望在不采取任何操作的情况下实现它。

Answer 1

你有两个选择：

一旦实例化MarketBloc，就从UI中添加一个事件

  MarketBloc()..add(MarketSelectEvent())

在初始化代码中添加事件

  MarketBloc() : super(MarketLoading()) {  
    add(MarketSelectEvent());
  }

Answer 2

您可以在应用程序加载的第一页的initState中执行此操作。

class TestPage extends StatefulWidget {
  @override
  State<TestPage> createState() => _TestPageState();
}

class _TestPageState extends State<TestPage> {
  late MarketBloc marketBloc;

  @override
  void initState() {
    super.initState();
    marketBloc = BlocProvider.of<MarketBloc>(context);
    marketBloc.add(MarketSelectEvent());
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: BlocBuilder<MarketBloc, MarketListState>(
          builder: (context, state) {
            if (state is MarketLoading) {
              return Text('loading...');
            }
            if (state is MarketDataFetched) {
              return ...your UI that contains data from API call
            }
          },
        ),
      ),
    );
  }
}