asyncredux-persistence

// Implement local state persistence using Persistor. Covers creating a custom Persistor class, implementing `readState()`, `persistDifference()`, `deleteState()`, using LocalPersist helper, throttling saves, and pausing/resuming persistence with app lifecycle.

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nameasyncredux-persistence

descriptionImplement local state persistence using Persistor. Covers creating a custom Persistor class, implementing `readState()`, `persistDifference()`, `deleteState()`, using LocalPersist helper, throttling saves, and pausing/resuming persistence with app lifecycle.

Overview

AsyncRedux provides state persistence by passing a persistor object to the Store. This maintains app state on disk, enabling restoration between sessions.

Store Initialization with Persistor

At startup, read any existing state from disk, create default state if none exists, then initialize the store:

var persistor = MyPersistor();

var initialState = await persistor.readState();

if (initialState == null) {
  initialState = AppState.initialState();
  await persistor.saveInitialState(initialState);
}

var store = Store<AppState>(
  initialState: initialState,
  persistor: persistor,
);

The Persistor Abstract Class

The Persistor<St> base class defines these methods:

abstract class Persistor<St> {
  /// Read persisted state, or return null if none exists
  Future<St?> readState();

  /// Delete state from disk
  Future<void> deleteState();

  /// Save state changes. Provides both newState and lastPersistedState
  /// so you can compare them and save only the difference.
  Future<void> persistDifference({
    required St? lastPersistedState,
    required St newState
  });

  /// Convenience method for initial saves
  Future<void> saveInitialState(St state) =>
    persistDifference(lastPersistedState: null, newState: state);

  /// Controls save frequency. Return null to disable throttling.
  Duration get throttle => const Duration(seconds: 2);
}

Creating a Custom Persistor

Extend the abstract class and implement the required methods:

class MyPersistor extends Persistor<AppState> {

  @override
  Future<AppState?> readState() async {
    // Read state from disk (e.g., from SharedPreferences, file, etc.)
    return null;
  }

  @override
  Future<void> deleteState() async {
    // Delete state from disk
  }

  @override
  Future<void> persistDifference({
    required AppState? lastPersistedState,
    required AppState newState,
  }) async {
    // Save state to disk.
    // You can compare lastPersistedState with newState to save only changes.
  }

  @override
  Duration get throttle => const Duration(seconds: 2);
}

Throttling

The throttle getter controls how often state is saved. All changes within the throttle window are collected and saved in a single call. The default is 2 seconds.

// Save at most every 5 seconds
@override
Duration get throttle => const Duration(seconds: 5);

// Disable throttling (save immediately on every change)
@override
Duration? get throttle => null;

Forcing Immediate Save

Dispatch PersistAction() to save immediately, bypassing the throttle:

store.dispatch(PersistAction());

Pausing and Resuming Persistence

Control persistence with these store methods:

store.pausePersistor();           // Pause saving
store.persistAndPausePersistor(); // Save current state, then pause
store.resumePersistor();          // Resume saving

App Lifecycle Integration

Pause persistence when the app goes to background and resume when it becomes active. Create an AppLifecycleManager widget:

class AppLifecycleManager extends StatefulWidget {
  final Widget child;

  const AppLifecycleManager({
    Key? key,
    required this.child,
  }) : super(key: key);

  @override
  _AppLifecycleManagerState createState() => _AppLifecycleManagerState();
}

class _AppLifecycleManagerState extends State<AppLifecycleManager>
    with WidgetsBindingObserver {

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    super.dispose();
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState lifecycle) {
    store.dispatch(ProcessLifecycleChange_Action(lifecycle));
  }

  @override
  Widget build(BuildContext context) => widget.child;
}

Create an action to handle lifecycle changes:

class ProcessLifecycleChange_Action extends ReduxAction<AppState> {
  final AppLifecycleState lifecycle;

  ProcessLifecycleChange_Action(this.lifecycle);

  @override
  Future<AppState?> reduce() async {
    if (lifecycle == AppLifecycleState.resumed ||
        lifecycle == AppLifecycleState.inactive) {
      store.resumePersistor();
    } else if (lifecycle == AppLifecycleState.paused ||
        lifecycle == AppLifecycleState.detached) {
      store.persistAndPausePersistor();
    } else {
      throw AssertionError(lifecycle);
    }
    return null;
  }
}

Wrap your app with the lifecycle manager:

StoreProvider<AppState>(
  store: store,
  child: AppLifecycleManager(
    child: MaterialApp( ... ),
  ),
)

LocalPersist Helper

The LocalPersist class simplifies disk operations for Android/iOS. It works with simple object structures containing only primitives, lists, and maps.

import 'package:async_redux/local_persist.dart';

// Create instance with a file name
var persist = LocalPersist("myFile");

// Save data
List<Object> simpleObjs = [
  'Hello',
  42,
  true,
  [100, 200, {"name": "John"}],
];
await persist.save(simpleObjs);

// Load data
List<Object> loaded = await persist.load();

// Append data
List<Object> moreObjs = ['more', 'data'];
await persist.save(moreObjs, append: true);

// File operations
int length = await persist.length();
bool exists = await persist.exists();
await persist.delete();

// JSON operations for single objects
await persist.saveJson(simpleObj);
Object? simpleObj = await persist.loadJson();

Note: LocalPersist only supports simple objects. For complex nested structures or custom classes, you need to implement serialization yourself (e.g., using JSON encoding with toJson/fromJson methods).

References

URLs from the documentation: