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Persist Redux State with custom storage engines and serializers

redux_persist pub package #

Persist Redux state across app restarts in Flutter, Web, or custom storage engines.


  • Save and load from multiple engine (Flutter, Web, File, custom)
  • Fully type safe
  • Transform state and raw on load/save
  • Custom serializers
  • Easy to use, integrate into your codebase in a few minutes!

Storage Engines:

Usage #

See Flutter example for a full overview.

The library creates a middleware that saves on every action.

State Setup #

We will be using the JsonSerializer, you will need to use a state class, with a required toJson method, as such:

class AppState {
  final int counter;

  AppState({this.counter = 0});

  AppState copyWith({int counter}) =>
      AppState(counter: counter ?? this.counter);

  // !!!
  static AppState fromJson(dynamic json) => AppState(counter: json["counter"]);

  // !!!
  dynamic toJson() => {'counter': counter};

(the copyWith method is optional, but a great helper. The fromJson is required as decoder, but can be renamed)

Persistor #

Next, create your persistor, storage engine, and store, then load the last state in. This will usually be in your main or in your root widget:

void main() async {
  // Create Persistor
  final persistor = Persistor<AppState>(
    storage: FileStorage(File("state.json")), // Or use other engines
    serializer: JsonSerializer<AppState>(AppState.fromJson), // Or use other serializers
  // Load initial state
  final initialState = await persistor.load();
  // Create Store with Persistor middleware
  final store = Store<AppState>(
    initialState: initialState ?? AppState(),
    middleware: [persistor.createMiddleware()],
  // ..

(JsonSerializer takes a single param which turns the JSON into your AppState. Your state will automatically be saved using the middleware)

Storage Engines #

You can use different storage engines for different application types:

  • Flutter

  • Web

  • FileStorage:

    final persistor = Persistor<AppState>(
      // ...
      storage: FileStorage(File("path/to/state")),
  • Build your own custom storage engine:

    To create a custom engine, you will need to implement the following interface to save/load a string to disk:

    abstract class StorageEngine {
      Future<void> save(Uint8List data);
      Future<Uint8List> load();

Serializers #

You can use one of the built in serializers such as:

  • JsonSerializer

  • StringSerializer

  • RawSerializer

  • Build your own serializer:

    To create a custom engine, you will need to implement the following interface to encode/decode state to/from Uint8List:

    abstract class StateSerializer<T> {
      Uint8List encode(T state);
      T decode(Uint8List data);


    class IntSerializer implements StateSerializer<int> {
      /// Takes [data] and converts it to a [int]
      int decode(Uint8List data) {
        return ByteData.view(data.buffer).getInt64(0);
      /// Takes [state] and converts it to a [Uint8List]
      Uint8List encode(int state) {
        final data = Uint8List(8);
        ByteData.view(data.buffer).setInt64(0, state);
        return data;

Whitelist/Blacklist #

To only save parts of your state, simply omit the fields that you wish to not save from your serializer.

If using the JsonSerializer, you can omit them from you toJson and decoder.

For instance, if we have a state with counter and name, but we don't want counter to be saved, you would do:

class AppState {
  final int counter;
  final String name;

  AppState({this.counter = 0,});

  // ...

  static AppState fromJson(dynamic json) =>
      AppState(name: json["name"]); // Don't load counter, will use default of 0

  Map toJson() => {'name': name}; // Don't save counter

Transforms #

Transformations are a way to transform ("edit") your state when loading/saving. They are 2 types:

All transformers are ran in order, from first to last.

Make sure all transformation are pure. Do not mutate the original state passed.

State #

State transformations transform your state before it's written to disk (on save) or loaded from disk (on load).

final persistor = Persistor<AppState>(
  // ...
  transforms: Transforms(
    onSave: [
      // Example: set counter to 3 when writing to disk
      (state) => state.copyWith(counter: 3),
    onLoad: [
      // Example: set counter to 0 when loading from disk
      (state) => state.copyWith(counter: 0),

Raw #

Raw transformation are applied to the raw byte (Uint8List) before it's saved/loaded.

final persistor = Persistor<AppState>(
  // ...
  rawTransforms: RawTransforms(
    onSave: [
      // Example: encrypt raw data
      (data) => encrypt(data),
    onLoad: [
      // Example: decrypt raw data
      (data) => decrypt(data),

Debug #

Persistor has a debug option, which will eventually log more debug information.

Use it like so:

final persistor = Persistor<AppState>(
  // ...
  debug: true

Throttle duration #

Persistor has a throttleDuration option, which will throttle saving to disk to prevent excessive writing. You should keep this at a low value to prevent data loss (few seconds is recommended).

Use it like so:

final persistor = Persistor<AppState>(
  // ...
  throttleDuration: Duration(seconds: 2),

Features and bugs #

Please file feature requests and bugs at the issue tracker.

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Persist Redux State with custom storage engines and serializers

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