Hydrated Bloc

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An extension to package:bloc which automatically persists and restores bloc and cubit states. Built to work with package:bloc.

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Overview

hydrated_bloc exports a Storage interface which means it can work with any storage provider. Out of the box, it comes with its own implementation: HydratedStorage.

HydratedStorage is built on top of hive for a platform-agnostic, performant storage layer. See the complete example for more details.

Usage

Setup HydratedStorage

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  HydratedBloc.storage = await HydratedStorage.build(storageDirectory: ...);
  runApp(App());
}

Create a HydratedCubit

class CounterCubit extends HydratedCubit<int> {
  CounterCubit() : super(0);

  void increment() => emit(state + 1);

  @override
  int fromJson(Map<String, dynamic> json) => json['value'] as int;

  @override
  Map<String, int> toJson(int state) => { 'value': state };
}

Create a HydratedBloc

abstract class CounterEvent {}
class CounterIncrementPressed extends CounterEvent {}

class CounterBloc extends HydratedBloc<CounterEvent, int> {
  CounterBloc() : super(0) {
    on<CounterIncrementPressed>((event, emit) => emit(state + 1));
  }

  @override
  int fromJson(Map<String, dynamic> json) => json['value'] as int;

  @override
  Map<String, int> toJson(int state) => { 'value': state };
}

Now the CounterCubit and CounterBloc will automatically persist/restore their state. We can increment the counter value, hot restart, kill the app, etc... and the previous state will be retained.

HydratedMixin

class CounterCubit extends Cubit<int> with HydratedMixin {
  CounterCubit() : super(0) {
    hydrate();
  }

  void increment() => emit(state + 1);

  @override
  int fromJson(Map<String, dynamic> json) => json['value'] as int;

  @override
  Map<String, int> toJson(int state) => { 'value': state };
}

Custom Storage Directory

Any storageDirectory can be used when creating an instance of HydratedStorage:

final storage = await HydratedStorage.build(
  storageDirectory: await getApplicationDocumentsDirectory(),
);

Custom Hydrated Storage

If the default HydratedStorage doesn't meet your needs, you can always implement a custom Storage by simply implementing the Storage interface and initializing HydratedBloc with the custom Storage.

// my_hydrated_storage.dart

class MyHydratedStorage implements Storage {
  @override
  dynamic read(String key) {
    // TODO: implement read
  }

  @override
  Future<void> write(String key, dynamic value) async {
    // TODO: implement write
  }

  @override
  Future<void> delete(String key) async {
    // TODO: implement delete
  }

  @override
  Future<void> clear() async {
    // TODO: implement clear
  }
}
// main.dart
HydratedBloc.storage = MyHydratedStorage();
runApp(MyApp());

Testing

When writing unit tests for code that uses HydratedBloc, it is recommended to stub the Storage implementation using package:mocktail.

import 'package:flutter_test/flutter_test.dart';
import 'package:hydrated_bloc/hydrated_bloc.dart';
import 'package:mocktail/mocktail.dart';

class MockStorage extends Mock implements Storage {}

void main() {
  late Storage storage;

  setUp(() {
    storage = MockStorage();
    when(
      () => storage.write(any(), any<dynamic>()),
    ).thenAnswer((_) async {});
    HydratedBloc.storage = storage;
  });

  // ...
}

You can also stub the storage.read API in individual tests to return cached state:

testWidgets('...', (tester) async {
  when<dynamic>(() => storage.read('$MyBloc')).thenReturn(MyState().toJson());

  // ...
});

Dart Versions

  • Dart 2: >= 2.12

Maintainers

Libraries

hydrated_bloc
An extension to package:bloc which automatically persists and restores bloc and cubit states. Built to work with package:bloc.