Flutter BLoC State Manager

Expert in Flutter state management with BLoC/Cubit, Riverpod, GoRouter navigation, and scalable architecture patterns.

Decision Points

State Solution Selection Tree

1. State Complexity Assessment:
   ├─ Simple data (boolean, enum, single value) 
   │  └─ Use: Cubit with copyWith pattern
   ├─ Event-driven logic (debounce, side effects, audit trail)
   │  └─ Use: BLoC with events/states
   ├─ Global app state with DI
   │  └─ Use: Riverpod StateNotifier
   └─ Widget-scoped state only
      └─ Use: Provider or setState

2. When choosing between BLoC packages:
   ├─ Need testing/debugging tools + state/event separation
   │  └─ flutter_bloc
   ├─ Want compile-time safety + automatic disposal
   │  └─ Riverpod
   ├─ Legacy codebase migration
   │  └─ Provider (then migrate to Cubit)
   └─ Simple state only
      └─ Cubit (via flutter_bloc)

3. Navigation Architecture Decision:
   ├─ Deep linking required OR type safety needed
   │  └─ GoRouter
   ├─ Nested navigation with bottom tabs
   │  └─ GoRouter with StatefulShellRoute
   ├─ Simple push/pop navigation only
   │  └─ Navigator.push (but prefer GoRouter for consistency)
   └─ Web app with URL routing
      └─ GoRouter (required)

Real-time Decision Matrix

Scenario	Cubit	BLoC	Riverpod	Provider
Form validation	✅	❌	✅	❌
API loading states	✅	⚠️	✅	⚠️
Event sourcing needed	❌	✅	❌	❌
Global auth state	⚠️	⚠️	✅	❌
Widget-only state	❌	❌	❌	✅

Failure Modes

1. Mutable State Mutation

• Symptom: UI doesn't rebuild after calling cubit methods
• Detection: emit(state.someList.add(item)) or direct property assignment
• Fix: Always use copyWith and return new instances; never mutate existing state objects

2. Listener Hell

• Symptom: Multiple BlocListeners wrapping widgets, performance issues, duplicate side effects
• Detection: Nested BlocListener widgets or same listener logic in multiple widgets
• Fix: Use MultiBlocListener or move side effects to cubit methods with single listener at route level

3. Rebuild Cascades

• Symptom: Entire screen rebuilds when only small part should update
• Detection: Every widget rebuilds on any state change, performance profiler shows excessive builds
• Fix: Split large state objects, use BlocSelector for granular rebuilds, proper widget tree structure

4. God State Object

• Symptom: Single state class with 10+ properties, copyWith method with massive parameter list
• Detection: State class >20 lines, copyWith with >8 parameters
• Fix: Split into feature-specific cubits; composition over god objects

5. Navigation State Conflicts

• Symptom: GoRouter redirect loops, navigation stack corruption, authentication redirects failing
• Detection: Browser back button breaks app, authentication status conflicts with routes
• Fix: Centralize auth state, use redirect guards properly, test deep link scenarios

Worked Examples

Complete E-commerce Cart Implementation

Scenario: Build shopping cart with add/remove items, quantity updates, price calculations, and checkout navigation.

1. State Design (Expert catches: immutability, separation of concerns)

// Novice: Single cart state with mutable list
// Expert: Immutable state with calculated properties
class CartState extends Equatable {
  final Map<String, CartItem> items;  // Expert: Use Map for O(1) lookups
  final CartStatus status;
  
  // Expert: Calculated properties prevent state inconsistency
  double get totalPrice => items.values.fold(0, (sum, item) => sum + item.total);
  int get itemCount => items.values.fold(0, (sum, item) => sum + item.quantity);
  
  CartState copyWith({Map<String, CartItem>? items, CartStatus? status}) {
    return CartState._(items ?? this.items, status ?? this.status);
  }
}

2. Decision Point Navigation: Adding item logic

• If item exists → update quantity via copyWith of Map
• If new item → add to Map copy
• If quantity becomes 0 → remove from Map

3. Implementation (Expert catches: performance, error handling)

class CartCubit extends Cubit<CartState> {
  Future<void> addItem(Product product, int quantity) async {
    final currentItems = Map<String, CartItem>.from(state.items);
    final existingItem = currentItems[product.id];
    
    if (existingItem != null) {
      // Expert: Immutable update of nested object
      currentItems[product.id] = existingItem.copyWith(
        quantity: existingItem.quantity + quantity
      );
    } else {
      currentItems[product.id] = CartItem.fromProduct(product, quantity);
    }
    
    emit(state.copyWith(items: currentItems));
    
    // Expert: Navigation coupling - delegate to router
    if (state.itemCount == 1) {
      context.go('/cart-overview');  // First item added
    }
  }
}

4. What Novice Misses vs Expert Catches:

• Novice: Direct list mutation state.items.add() → UI won't rebuild
• Expert: Map copying with proper immutability
• Novice: Business logic in widget build() method
• Expert: All logic in cubit, widgets only render and dispatch
• Novice: No error handling for network failures
• Expert: Loading/error states in every async operation

Quality Gates

• All state classes extend Equatable with props override
• Every async operation has loading/success/error states
• CopyWith method covers all state properties
• No business logic in widget build() methods
• BlocTest coverage >90% for all state transitions
• Widget tests verify UI for each state enum value
• GoRouter redirect guards prevent infinite loops
• Deep link navigation tested (manual + automated)
• BlocObserver configured for debug logging
• Repository interfaces abstract data layer access
• Feature modules export single barrel file
• No God state objects (>8 copyWith parameters = split)

NOT-FOR Boundaries

This skill should NOT be used for:

• React Native state → Use react-native-architect instead
• SwiftUI data flow → Use swiftui-data-flow-expert instead
• Jetpack Compose navigation → Use jetpack-compose-navigation-expert instead
• Flutter UI/widgets only → Use flutter-ui-specialist instead
• Backend API design → Use api-architect instead
• Database schema design → Use database-architect instead
• Widget-only state (no business logic) → Use built-in setState instead
• Static data/constants → Use simple Dart classes, not state management
• Animation controllers → Use Flutter's AnimationController directly

Delegate to other skills when:

• Complex offline sync needed → mobile-offline-sync-architect
• Performance optimization required → flutter-performance-expert
• Architecture decisions beyond state → frontend-architect