錯誤 State：調用關閉后無法添加新事件 - Flutter 模塊化

Question

當我返回主頁並第二次訪問 ProductsPage 時，我遇到以下錯誤“錯誤 State：調用關閉后無法添加新事件” 。

產品也是第一次加載但是當我嘗試再次加載 ProductsPage 時，會拋出此錯誤。

import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:flutter_modular/flutter_modular.dart';

import '../../widgets/product_display.dart';
import '../../widgets/title_section.dart';
import '../home_page/components/button_menu.dart';
import 'bloc/products_bloc.dart';
import 'bloc/products_event.dart';
import 'bloc/products_state.dart';

class ProductsPage extends StatefulWidget {
  const ProductsPage({Key? key}) : super(key: key);

  @override
  State<ProductsPage> createState() => _ProductsPageState();
}

class _ProductsPageState extends State<ProductsPage> {
  final bloc = Modular.get<ProductsBloc>();

  @override
  void initState() {
    super.initState();
    bloc.add(LoadProductsEvent());
  }

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Produtos'),
      ),
      body: SafeArea(
        child: SingleChildScrollView(
            child: Padding(
          padding: const EdgeInsets.all(10.0),
          child: Column(
            children: [
              const SizedBox(
                height: 10,
              ),
              const TextField(),
              const TitleSection(title: 'Categorias'),
              Container(
                  margin: const EdgeInsets.all(10),
                  height: 120,
                  child: ListView(
                    scrollDirection: Axis.horizontal,
                    children: [
                      ButtonMenu(
                          action: () {},
                          buttonName: 'Vestuário',
                          icon: Icons.store_mall_directory_rounded),
                      ButtonMenu(
                          action: () {},
                          buttonName: 'Jogos',
                          icon: Icons.sports_esports_outlined),
                      ButtonMenu(
                          action: () {},
                          buttonName: 'Vouchers',
                          icon: Icons.feed_outlined),
                      ButtonMenu(
                          action: () {},
                          buttonName: 'Moskelines',
                          icon: Icons.menu_book_outlined),
                      ButtonMenu(
                          action: () {},
                          buttonName: 'Blusas',
                          icon: Icons.paid_outlined),
                    ],
                  )),
              Container(
                margin: const EdgeInsets.all(10),
                height: MediaQuery.of(context).size.height,
                child: BlocBuilder<ProductsBloc, ProductsState>(
                  bloc: bloc,
                  builder: (context, state) {
                    final state = bloc.state;

                    if (state is ProductInicialState) {
                      return const Center(
                        child: CircularProgressIndicator(),
                      );
                    } else if (state is ProductSuccessState) {
                      final productsList = state.products;
                      return GridView.builder(
                        gridDelegate:
                            const SliverGridDelegateWithFixedCrossAxisCount(
                          childAspectRatio: 0.7,
                          crossAxisCount: 2,
                          crossAxisSpacing: 10,
                          mainAxisSpacing: 10,
                        ),
                        itemCount: productsList.length,
                        itemBuilder: (context, index) {
                          final item = productsList[index];
                          return ProductDisplay(
                              productEntity: productsList[index],
                              icon: Icons.store_mall_directory_rounded,
                              productName: item.productName,
                              action: () {});
                        },
                      );
                    } else {
                      return Container();
                    }
                  },
                ),
              ),
              const TitleSection(title: 'Produtos'),
            ],
          ),
        )),
      ),
    );
  }
}

我的集團代碼是：

import 'package:bloc/bloc.dart';

import 'package:ConfidentialName/domain/usecases/get_all_products_usecase.dart';

import 'products_event.dart';
import 'products_state.dart';

class ProductsBloc extends Bloc<ProductsEvent, ProductsState> {
  final GetAllProductsUsecase usecase;

  ProductsBloc(
    this.usecase,
  ) : super(ProductInicialState()) {
    on<LoadProductsEvent>((event, emit) async {
      final result = await usecase.getAllProducts();
      result.fold((l) => emit.call(ProductErrorState(l)),
          (list) => emit.call(ProductSuccessState(list)));
    });
  }
}

我不明白為什么會發生此錯誤

Answer 1

只需在發出狀態之前檢查 bloc 是否已關閉。

if(isClosed) return; // Here
result.fold((l) => emit.call(ProductErrorState(l)),
          (list) => emit.call(ProductSuccessState(list)));

另外，如果您想發出狀態，請確保您沒有處理該集團，

像這樣發起集團

late ProductsBloc bloc;

  @override
  void initState() {
    super.initState();
    bloc = Modular.get<ProductsBloc>();
    bloc.add(LoadProductsEvent());
  }

Answer 2

當您將 bloc 綁定為 Singleton 時，flutter_modular 會發生這種情況。將其更改為 app_module 文件中的 Bind.factory（依賴注入）。