2026年のFlutter状態管理：Riverpod vs Bloc vs GetX 徹底比較ガイド

import 'package:riverpod_annotation/riverpod_annotation.dart';

part 'counter_provider.g.dart';

// Code generation ensures compile-time safety
@riverpod
class Counter extends _$Counter {
  @override
  int build() => 0; // Initial state

  void increment() => state = state + 1;
  void decrement() => state = state - 1;
  void reset() => state = 0;
}

import 'package:riverpod_annotation/riverpod_annotation.dart';

part 'user_repository_provider.g.dart';

@riverpod
Future<User> currentUser(Ref ref) async {
  final authService = ref.watch(authServiceProvider);
  final userId = authService.currentUserId;

  // Auto-retry on network failure (Riverpod 3.0)
  final response = await ref.watch(
    httpClientProvider,
  ).get('/api/users/$userId');

  return User.fromJson(response.data);
}

sealed class AuthenticationEvent {}

final class LoginRequested extends AuthenticationEvent {
  final String email;
  final String password;
  LoginRequested({required this.email, required this.password});
}

final class LogoutRequested extends AuthenticationEvent {}

final class SessionRestored extends AuthenticationEvent {
  final String token;
  SessionRestored({required this.token});
}

import 'package:flutter_bloc/flutter_bloc.dart';

class AuthenticationBloc
    extends Bloc<AuthenticationEvent, AuthenticationState> {
  final AuthRepository _authRepo;
  final TokenStorage _tokenStorage;

  AuthenticationBloc({
    required AuthRepository authRepo,
    required TokenStorage tokenStorage,
  })  : _authRepo = authRepo,
        _tokenStorage = tokenStorage,
        super(AuthenticationInitial()) {
    on<LoginRequested>(_onLoginRequested);
    on<LogoutRequested>(_onLogoutRequested);
    on<SessionRestored>(_onSessionRestored);
  }

  Future<void> _onLoginRequested(
    LoginRequested event,
    Emitter<AuthenticationState> emit,
  ) async {
    emit(AuthenticationLoading());
    try {
      final token = await _authRepo.login(
        email: event.email,
        password: event.password,
      );
      await _tokenStorage.save(token);
      emit(AuthenticationSuccess(token: token));
    } catch (e) {
      emit(AuthenticationFailure(message: e.toString()));
    }
  }

  Future<void> _onLogoutRequested(
    LogoutRequested event,
    Emitter<AuthenticationState> emit,
  ) async {
    await _tokenStorage.clear();
    emit(AuthenticationInitial());
  }

  Future<void> _onSessionRestored(
    SessionRestored event,
    Emitter<AuthenticationState> emit,
  ) async {
    emit(AuthenticationSuccess(token: event.token));
  }
}

import 'package:bloc_concurrency/bloc_concurrency.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

class SearchBloc extends Bloc<SearchEvent, SearchState> {
  final SearchRepository _repository;

  SearchBloc({required SearchRepository repository})
      : _repository = repository,
        super(SearchInitial()) {
    // restartable() cancels previous search on new input
    on<SearchQueryChanged>(
      _onQueryChanged,
      transformer: restartable(),
    );
    // droppable() ignores events while processing
    on<SearchResultSelected>(
      _onResultSelected,
      transformer: droppable(),
    );
  }

  Future<void> _onQueryChanged(
    SearchQueryChanged event,
    Emitter<SearchState> emit,
  ) async {
    if (event.query.length < 3) {
      emit(SearchInitial());
      return;
    }
    emit(SearchLoading());
    final results = await _repository.search(event.query);
    emit(SearchLoaded(results: results));
  }

  Future<void> _onResultSelected(
    SearchResultSelected event,
    Emitter<SearchState> emit,
  ) async {
    emit(SearchNavigating(result: event.result));
  }
}

import 'package:get/get.dart';

// Global singleton - difficult to test and scope
class CounterController extends GetxController {
  final count = 0.obs; // Reactive observable

  void increment() => count.value++;
  void decrement() => count.value--;

  // Lifecycle hooks - disposal timing is unpredictable
  @override
  void onClose() {
    // Cleanup may not execute reliably
    super.onClose();
  }
}

// Usage in widget
class CounterPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // Get.put creates a global singleton
    final controller = Get.put(CounterController());
    return Obx(() => Text('${controller.count}'));
  }
}

// Step 1: Replace GetX controller with Riverpod notifier
// Before (GetX)
class ProductController extends GetxController {
  final products = <Product>[].obs;
  final isLoading = false.obs;

  Future<void> loadProducts() async {
    isLoading.value = true;
    products.value = await ProductApi.fetchAll();
    isLoading.value = false;
  }
}

// After (Riverpod 3.0)
@riverpod
class ProductList extends _$ProductList {
  @override
  Future<List<Product>> build() async {
    // Auto-retry on failure, auto-pause when off-screen
    return ProductApi.fetchAll();
  }

  Future<void> refresh() async {
    ref.invalidateSelf();
  }
}

// Step 2: Replace widget bindings
// Before (GetX)
class ProductPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final ctrl = Get.put(ProductController());
    return Obx(() {
      if (ctrl.isLoading.value) return CircularProgressIndicator();
      return ListView.builder(
        itemCount: ctrl.products.length,
        itemBuilder: (_, i) => ProductTile(ctrl.products[i]),
      );
    });
  }
}

// After (Riverpod 3.0)
class ProductPage extends ConsumerWidget {
  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final productsAsync = ref.watch(productListProvider);
    return productsAsync.when(
      loading: () => const CircularProgressIndicator(),
      error: (err, stack) => ErrorDisplay(error: err),
      data: (products) => ListView.builder(
        itemCount: products.length,
        itemBuilder: (_, i) => ProductTile(products[i]),
      ),
    );
  }
}

// Riverpod test - isolated container
import 'package:flutter_test/flutter_test.dart';
import 'package:riverpod/riverpod.dart';

void main() {
  test('Counter increments', () {
    final container = ProviderContainer.test();
    // Override dependencies for isolation
    final counter = container.read(counterProvider.notifier);

    expect(container.read(counterProvider), 0);
    counter.increment();
    expect(container.read(counterProvider), 1);
  });
}

// Bloc test - event-driven verification
import 'package:bloc_test/bloc_test.dart';
import 'package:flutter_test/flutter_test.dart';

void main() {
  blocTest<AuthenticationBloc, AuthenticationState>(
    'emits [loading, success] on valid login',
    build: () => AuthenticationBloc(
      authRepo: MockAuthRepo(),
      tokenStorage: MockTokenStorage(),
    ),
    act: (bloc) => bloc.add(
      LoginRequested(email: 'dev@test.com', password: 'secure123'),
    ),
    expect: () => [
      isA<AuthenticationLoading>(),
      isA<AuthenticationSuccess>(),
    ],
  );
}