1. What are best practices for implementing state management in Flutter? How do you structure state for scalability?
Separate state into categories: app state (global, survives across screens like authentication), screen state (lives with a screen like form state), and local state (widget-specific like expanded/collapsed). Use setState for local state, shared state management for app/screen state. Don't overuse global state - keep state as local as possible, lifting it only when sharing is necessary. Organize state by feature rather than by type - group related models, controllers, and UI in feature folders rather than all models together. This makes code easier to navigate and maintain. Keep business logic out of widgets - widgets should be thin presentation layer calling methods on controllers or blocs rather than containing logic. This separation enables testing business logic without widget tests. Use immutable state objects with copy methods (consider freezed package) to prevent accidental mutations and make state changes explicit. This is especially important with Bloc and Redux patterns. For Provider/Riverpod, immutability prevents subtle bugs where changes don't trigger rebuilds. Define clear APIs for state modifications - expose methods rather than direct property access, ensuring validation and notifications happen correctly. Implement error handling in state - don't just store success data, include error and loading states. Use sealed classes or enums to represent different states (loading, success, error) ensuring UI handles all cases. Test state logic thoroughly - business logic in controllers/blocs/cubits should have high test coverage since it's easy to test without UI. Profile your app to identify rebuild performance issues and optimize with targeted rebuilds, const widgets, and appropriate state scoping.