Injectable环境下MovieWatcherBloc依赖未注册StreamSubscription报错

问题根源 #

你在MovieWatcherBloc的构造函数中把StreamSubscription声明为依赖参数，要求Injectable为你注入这个对象，但StreamSubscription是动态创建的订阅对象，不属于需要依赖注入的服务/仓库类，Injectable无法注册也不应该管理它。

修改步骤 #

1. 移除构造函数中的StreamSubscription参数，将其改为Bloc内部的成员变量，自行初始化和管理。
2. 调整订阅逻辑：首次订阅前不需要执行cancel（初始状态下订阅对象为null），避免空指针异常。
3. 安全处理订阅销毁：在close方法中先判断订阅是否存在，再执行cancel。

修改后的完整代码 #

import 'dart:async';
import 'package:app_3/Domain/auth/notes/i_movie_repository.dart';
import 'package:app_3/Domain/auth/notes/list.dart';
import 'package:app_3/Domain/auth/notes/note_failure.dart';
import 'package:bloc/bloc.dart';
import 'package:dartz/dartz.dart';
import 'package:freezed_annotation/freezed_annotation.dart';
import 'package:injectable/injectable.dart';
import 'package:kt_dart/kt.dart';

part 'movie_watcher_event.dart';
part 'movie_watcher_state.dart';
part 'movie_watcher_bloc.freezed.dart';

@injectable
class MovieWatcherBloc extends Bloc<MovieWatcherEvent, MovieWatcherState> {
  final INoteRepository _noteRepository;
  // 改为内部成员变量，初始为null
  StreamSubscription<Either<NoteFailure, KtList<Mlist>>>? _noteStreamSubscription;

  // 构造函数只保留仓库依赖
  MovieWatcherBloc(this._noteRepository)
      : super(const MovieWatcherState.initial()) {
    @override
    Stream<MovieWatcherState> mapEventToState(
      MovieWatcherEvent event,
    ) async* {
      yield* event.map(watchAllstarted: (e) async* {
        yield const MovieWatcherState.loadInProgress();
        // 先判断订阅是否存在，再取消
        await _noteStreamSubscription?.cancel();
        // 创建新的订阅
        _noteStreamSubscription = _noteRepository.watchAll().listen(
              (failureOrNotes) => add(MovieWatcherEvent.moviesReceived(failureOrNotes)),
            );
      }, watchUncompletedstarted: (e) async* {
        yield const MovieWatcherState.loadInProgress();
        await _noteStreamSubscription?.cancel();
        _noteStreamSubscription = _noteRepository.watchUncompleted().listen(
              (failureOrNotes) => add(MovieWatcherEvent.moviesReceived(failureOrNotes)),
            );
      }, moviesReceived: (e) async* {
        yield e.failureOrNotes.fold(
          (f) => MovieWatcherState.loadFailure(f),
          (lists) => MovieWatcherState.loadSuccess(lists),
        );
      });
    }
  }

  @override
  Future<void> close() async {
    // 安全取消订阅
    await _noteStreamSubscription?.cancel();
    return super.close();
  }
}

后续验证 #

1. 重新运行build_runner：

flutter pub run build_runner watch --delete-conflicting-outputs

此时之前的依赖未注册警告会消失。
2. 运行应用，GetIt找不到对象的错误也会解决。

内容的提问来源于stack exchange，提问作者nidhin ninan