State ManagementIntermediate30 XP3 min read
How do you persist BLoC/Cubit state across app restarts?
TL;DR: Use HydratedBloc/HydratedCubit from the hydrated_bloc package. It automatically serializes state to local storage and rehydrates it on the next app launch.
Full Answer
HydratedBloc extends the standard BLoC library with automatic state persistence using a storage backend (default: HydratedStorage backed by hive).
Override fromJson and toJson in your Bloc/Cubit to define serialization. On startup, HydratedBloc calls fromJson with the stored data to restore the last state.
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Don't persist sensitive data (tokens, passwords) via HydratedBloc — it uses unencrypted local storage. Use flutter_secure_storage for sensitive data.
Code Examples
dartHydratedCubit for theme persistence
Output
On first launch: ThemeMode.system. After setTheme(ThemeMode.dark) + app restart: ThemeMode.dark restored automatically
Common Mistakes
- ✗Forgetting HydratedBloc.storage setup in main() — throws uninitialized storage error
- ✗Returning null from toJson — clears the persisted state silently
Interview Tip
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HydratedBloc is a great answer to 'how do you handle offline persistence in BLoC apps?' — shows practical library knowledge.
#HydratedBloc#persistence#SharedPreferences#offline