prefer_multi_bloc_provider

v0.4.0 Warning Fix Bloc / Riverpod

This rule flags a BlocProvider, BlocListener or RepositoryProvider whose child: is another widget of the same type, and offers a quick fix collapsing the nest into MultiBlocProvider, MultiBlocListener or MultiRepositoryProvider.

Only the outermost provider of a nest is reported, so a three-deep pyramid produces one diagnostic, not two.

Why use this rule

The nested and the flattened forms behave identically — this is readability. A Multi* list is a flat list of providers: adding one is a one-line diff, and removing one does not require re-indenting everything below it. A nest makes every such change touch the whole block.

Examples

The app-root provider pyramid

// Don't — one diagnostic, on the outermost BlocProvider
import 'package:flutter/widgets.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

sealed class CounterEvent {}

class CounterBloc extends Bloc<CounterEvent, int> {
  CounterBloc() : super(0);
}

class TimerCubit extends Cubit<int> {
  TimerCubit() : super(0);
}

class ThemeCubit extends Cubit<bool> {
  ThemeCubit() : super(false);
}

Widget buildApp(Widget home) => BlocProvider<CounterBloc>(
  create: (context) => CounterBloc(),
  child: BlocProvider<TimerCubit>(
    create: (context) => TimerCubit(),
    child: BlocProvider<ThemeCubit>(
      create: (context) => ThemeCubit(),
      child: home,
    ),
  ),
);

// Do — the quick fix produces this
import 'package:flutter/widgets.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

sealed class CounterEvent {}

class CounterBloc extends Bloc<CounterEvent, int> {
  CounterBloc() : super(0);
}

class TimerCubit extends Cubit<int> {
  TimerCubit() : super(0);
}

class ThemeCubit extends Cubit<bool> {
  ThemeCubit() : super(false);
}

Widget buildApp(Widget home) => MultiBlocProvider(
  providers: [
    BlocProvider<CounterBloc>(create: (context) => CounterBloc()),
    BlocProvider<TimerCubit>(create: (context) => TimerCubit()),
    BlocProvider<ThemeCubit>(create: (context) => ThemeCubit()),
  ],
  child: home,
);

Listeners nest the same way

// Don't
BlocListener<AuthBloc, bool>(
  listener: (context, loggedIn) {},
  child: BlocListener<CartBloc, int>(
    listener: (context, count) {},
    child: const HomeView(),
  ),
)

// Do
MultiBlocListener(
  listeners: [
    BlocListener<AuthBloc, bool>(listener: (context, loggedIn) {}),
    BlocListener<CartBloc, int>(listener: (context, count) {}),
  ],
  child: const HomeView(),
)

Known limitations

Only a nest of the same type is reported. A BlocProvider wrapping a RepositoryProvider cannot be collapsed into one Multi* widget, so it is left alone:

// Not reported — different types, nothing to merge
RepositoryProvider<UserRepository>(
  create: (context) => UserRepository(),
  child: BlocProvider<AuthBloc>(
    create: (context) => AuthBloc(),
    child: const HomeView(),
  ),
)

The nesting must go through child:. A provider reached through any other argument, or through a builder callback, is not matched.

Configuration

This rule is in the opinionated preset, so it is on with preset: opinionated, or by name:

rules:
  prefer_multi_bloc_provider: true

To turn it off again:

rules:
  prefer_multi_bloc_provider: false

To keep the rule on but skip certain paths, use per-rule exclude.

avoid_bloc_public_methods — Prevent public methods, getters, and setters in Bloc classes.
avoid_duplicate_bloc_event_handlers — Register each bloc event type exactly once.
avoid_passing_bloc_to_bloc — Prevent Bloc/Cubit classes from depending on other Bloc/Cubit instances.
emit_new_bloc_state_instances — Emit a new state instance instead of the existing state object.