Does get_it have a real use with bloc?

Question

The following code is part of a tutorial about Bloc:

service_locator.dart

final getIt = GetIt.instance;


void serviceLocatorInit() {
  getIt
    ..registerSingleton(UsernameCubit())
    ..registerSingleton(RouterSimpleCubit())
    ..registerSingleton(CounterCubit())
    ..registerSingleton(ThemeCubit())
    ..registerSingleton(GuestsBloc())
    ..registerSingleton(PokemonCubit())
    ..registerSingleton(HistoricLocationBloc())
    ..registerSingleton(
      GeolocationCubit(getIt<HistoricLocationBloc>().onNewUserLocation)..watchUserLocation()
    )
  ;
}

main.dart

void main() {
  serviceLocatorInit();
  runApp(const BlocsProviders());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    final appRouter = context.read<RouterSimpleCubit>().state;
    final theme = context.watch<ThemeCubit>().state;

    return MaterialApp.router(
      title: 'Welcome to Flutter',
      debugShowCheckedModeBanner: false,
      theme: AppTheme(isDarkmode: theme.isDarkMode).getTheme(),
      routerConfig: appRouter,
    );
  }
}


class BlocsProviders extends StatelessWidget {
  const BlocsProviders({super.key});

  @override
  Widget build(BuildContext context) {
    return MultiBlocProvider(
      providers: [
        BlocProvider(create: (_) => getIt<UsernameCubit>()),
        BlocProvider(create: (_) => getIt<RouterSimpleCubit>()),
        BlocProvider(create: (_) => getIt<CounterCubit>()),
        BlocProvider(create: (_) => getIt<ThemeCubit>()),
        BlocProvider(create: (_) => getIt<GuestsBloc>()),
        BlocProvider(create: (_) => getIt<PokemonCubit>()),
        BlocProvider(create: (_) => getIt<GeolocationCubit>()),
        BlocProvider(create: (_) => getIt<HistoricLocationBloc>()),
      ], 
      child: const MyApp(),
    );
  }
}

I have this question: is there some relevant use for get_it package in this code? because the author uses context.read or BlocBuilder for the rest of tutorial and in my opinion that makes irrelevant the use of get_it since BlocProvider already injects Bloc objects.

Answer 1

You're totally right! The creator of the flutter_bloc package himself advised against using get_it to provide the instance of a Bloc or Cubit to a BlocProvider because it's already doing all the work of injecting your bloc:

[...] I recommend not mixing BlocProvider with get_it but the immediate fix would be to change the bloc/cubit registrations to be factories instead of lazy singletons.

Felix Angelov, Jan 19, 2022

The point of using a service locator is to simplify the replacement of an instance (often for testing) BlocProvider is already enough because you can already easily override the instance of a Bloc/Cubit you're refering to by wrapping your widget inside a new BlocProvider/MultiBlocProvider.

Personally, I use get_it to handle the injection of my repositories, use cases and datasources, but using it to inject the instance provided by a BlocProvider is just overkill and might even cause some weird behavior in some cases.