2nd/10_Wiki/Topic_Programming/Architecture/BLoC.md

id, title, category, status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, verification_status, tags, raw_sources, last_reinforced, github_commit, tech_stack

id	title	category	status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	verification_status	tags	raw_sources	last_reinforced	github_commit	tech_stack
wiki-2026-0508-bloc	BLoC	10_Wiki/Topics	verified	self	BLoC Business Logic Component flutter_bloc	none	A	0.9	applied	flutter state-management dart reactive		2026-05-10	pending	language framework dart flutter,flutter_bloc

BLoC

매 한 줄

"매 UI ↔ business logic 의 strict separation — Event in · State out · Stream 으로 의 mediate". 2018 Felix Angelov · Paolo Soares Google I/O 의 introduce, 2026 의 flutter_bloc 9.x · Cubit · Hydrated 의 Flutter ecosystem 의 dominant state-management.

매 핵심

매 contract

• Event: input (button tap · API tick).
• State: output (immutable snapshot).
• Bloc: mapEventToState (legacy) → on<Event> handler (modern 8.x+).
• Cubit: simpler — 매 event 의 X, method 의 emit 의 directly.

매 component

• BlocProvider — DI · scope.
• BlocBuilder — rebuild 의 state change 의 reactive.
• BlocListener — side-effect (snackbar · navigation).
• BlocConsumer — builder + listener.
• RepositoryProvider — data layer DI.

매 응용

1. 매 Flutter 의 production app (BMW · Nubank · Alibaba).
2. Form validation (매 reactive validation per field).
3. Authentication flow.
4. Hydrated state (매 disk-persisted, app restart 의 survive).

💻 패턴

Bloc (event-driven)

sealed class CounterEvent {}
class Increment extends CounterEvent {}
class Decrement extends CounterEvent {}

class CounterBloc extends Bloc<CounterEvent, int> {
  CounterBloc() : super(0) {
    on<Increment>((event, emit) => emit(state + 1));
    on<Decrement>((event, emit) => emit(state - 1));
  }
}

// usage
BlocProvider(
  create: (_) => CounterBloc(),
  child: BlocBuilder<CounterBloc, int>(
    builder: (ctx, count) => Text('$count'),
  ),
)

Cubit (simpler · method-based)

class CounterCubit extends Cubit<int> {
  CounterCubit() : super(0);
  void increment() => emit(state + 1);
  void decrement() => emit(state - 1);
}

// trigger
context.read<CounterCubit>().increment();

Async event handler with state machine

sealed class LoginState {}
class LoginInitial   extends LoginState {}
class LoginLoading   extends LoginState {}
class LoginSuccess   extends LoginState { final User user; LoginSuccess(this.user); }
class LoginFailure   extends LoginState { final String msg; LoginFailure(this.msg); }

class LoginBloc extends Bloc<LoginEvent, LoginState> {
  final AuthRepository auth;
  LoginBloc(this.auth) : super(LoginInitial()) {
    on<SubmitLogin>(_onSubmit);
  }

  Future<void> _onSubmit(SubmitLogin e, Emitter<LoginState> emit) async {
    emit(LoginLoading());
    try {
      final user = await auth.login(e.email, e.password);
      emit(LoginSuccess(user));
    } catch (err) {
      emit(LoginFailure(err.toString()));
    }
  }
}

BlocListener (side-effect)

BlocListener<LoginBloc, LoginState>(
  listener: (ctx, state) {
    if (state is LoginSuccess) Navigator.pushNamed(ctx, '/home');
    if (state is LoginFailure) ScaffoldMessenger.of(ctx).showSnackBar(
      SnackBar(content: Text(state.msg)),
    );
  },
  child: LoginForm(),
)

Hydrated Bloc (auto-persist)

class SettingsCubit extends HydratedCubit<Settings> {
  SettingsCubit() : super(const Settings(theme: 'light'));

  void setTheme(String t) => emit(state.copyWith(theme: t));

  @override
  Settings fromJson(Map<String, dynamic> json) => Settings.fromJson(json);

  @override
  Map<String, dynamic> toJson(Settings state) => state.toJson();
}

Stream-debounced search Bloc

class SearchBloc extends Bloc<SearchQuery, SearchState> {
  SearchBloc(this.api) : super(SearchInitial()) {
    on<SearchQuery>(
      _onSearch,
      transformer: (events, mapper) => events
          .debounceTime(const Duration(milliseconds: 300))
          .switchMap(mapper),
    );
  }

  Future<void> _onSearch(SearchQuery e, Emitter<SearchState> emit) async {
    emit(SearchLoading());
    final results = await api.search(e.term);
    emit(SearchLoaded(results));
  }
}

Test (bloc_test)

blocTest<CounterBloc, int>(
  'emits [1] when Increment is added',
  build: () => CounterBloc(),
  act: (b) => b.add(Increment()),
  expect: () => [1],
);

매 결정 기준

상황	Approach
Simple state · single screen	Cubit
Complex event flow · undo/redo	Bloc
Persisted state	HydratedBloc/Cubit
Server-driven · realtime	Bloc + StreamSubscription
Multi-screen shared	BlocProvider 의 root
매 small project	Provider · Riverpod

기본값: Cubit 의 first, Bloc 의 event 의 explicit 의 require 의 case.

🔗 Graph

• 부모: State Management
• 응용: Clean Architecture
• Adjacent: Provider · Riverpod

🤖 LLM 활용

언제: Bloc · Cubit · Event · State 의 boilerplate 의 generate, blocTest 의 draft. 언제 X: 매 actual event sequencing · concurrency strategy (debounce/restartable/sequential) — 매 domain 의 understand 의 require.

❌ 안티패턴

• State 의 mutable: 매 immutable + copyWith 의 mandatory.
• BlocBuilder 의 entire screen 의 wrap: granular rebuild 의 lose — multiple builder 의 split.
• Bloc 의 navigation 의 directly do: side-effect 의 BlocListener 의 isolate.
• Singleton bloc 의 manual instantiate: BlocProvider 의 use — lifecycle 의 leak prevent.

🧪 검증 / 중복

• Verified (bloclibrary.dev, flutter_bloc 9.x docs, Felix Angelov GitHub).
• 신뢰도 A.

🕓 Changelog

날짜	변경
2026-05-08	Phase 1
2026-05-10	Manual cleanup — Bloc + Cubit + Hydrated + bloc_test patterns