React Native Academy · レッスン

AsyncStorageによるZustand Stateの永続化

AsyncStorageを基盤とするpersistミドルウェアでZustand storeをラップし、アプリを再起動してもstateが保持されるようにして、再ハイドレーションのタイミングを扱います

「AsyncStorageによるZustand Stateの永続化」はCoddyKit上の無料React Native Academyレッスンです。これはレッスン3/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはReact Native Academy学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 React Native Academyコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Why Persist State?

By default, Zustand state lives only in memory and is lost when the app closes. Persisting state means saving it to the device's local storage so it survives app restarts. This is essential for user preferences, authentication tokens, shopping carts, or any data the user expects to still be there when they reopen the app.

Installing AsyncStorage

AsyncStorage is the standard key-value storage API for React Native. In Expo managed workflow, install the community package @react-native-async-storage/async-storage. Zustand's built-in persist middleware works with any storage adapter, and AsyncStorage is the most common choice for mobile apps.

npx expo install @react-native-async-storage/async-storage

Adding the persist Middleware

Wrap the store creator with persist imported from zustand/middleware. Pass it your store factory and a configuration object with a name key (the AsyncStorage key where state will be saved) and a storage key (pointing to your AsyncStorage adapter). Zustand handles reading and writing automatically.

import { create } from 'zustand';
import { persist, createJSONStorage } from 'zustand/middleware';
import AsyncStorage from '@react-native-async-storage/async-storage';

export const useSettingsStore = create(
  persist<SettingsStore>(
    (set) => ({
      theme: 'light',
      notifications: true,
      setTheme: (theme) => set({ theme }),
      toggleNotifications: () =>
        set((state) => ({ notifications: !state.notifications })),
    }),
    {
      name: 'settings-store',
      storage: createJSONStorage(() => AsyncStorage),
    }
  )
);

How Persist Works Internally

When the store is first created, persist reads from AsyncStorage and rehydrates (restores) any previously saved state before rendering the first component. When state changes via set, persist automatically serializes the state to JSON and writes it to AsyncStorage asynchronously. This all happens without any extra code in your components.

Handling the Rehydration Delay

AsyncStorage reads are asynchronous, so on the first render the store may still contain the initial state before rehydration finishes. Zustand's persist middleware adds a _hasHydrated flag and an onFinishHydration callback. Use these to show a loading screen while persisted state is loading from disk.

const hasHydrated = useSettingsStore((state) => state._hasHydrated);

if (!hasHydrated) {
  return <ActivityIndicator />; // Show loading until store is ready
}

// Alternatively, listen to hydration completion:
useEffect(() => {
  const unsub = useSettingsStore.persist.onFinishHydration(() => {
    setReady(true);
  });
  return unsub;
}, []);

Persisting Only Part of the State

You often do not want to persist everything in the store — for example, transient loading states or error messages should not be saved. Use the partialize option to select which fields to persist. The returned object contains only the keys you want to write to AsyncStorage.

persist<AuthStore>(
  (set) => ({
    user: null,
    token: null,
    isLoading: false,    // transient — don't persist
    error: null,         // transient — don't persist
    login: (user, token) => set({ user, token }),
    logout: () => set({ user: null, token: null }),
  }),
  {
    name: 'auth-store',
    storage: createJSONStorage(() => AsyncStorage),
    partialize: (state) => ({ user: state.user, token: state.token }),
  }
)

Versioning and Migration

When you change the structure of your persisted state in a new app release, old data on users' devices may not match the new shape. Use the version and migrate options to upgrade stored state from one version to the next. Increment version with each structural change and handle old state in the migrate function.

persist<SettingsStore>(
  (set) => ({ /* ... */ }),
  {
    name: 'settings-store',
    storage: createJSONStorage(() => AsyncStorage),
    version: 2,
    migrate: (persistedState: any, version: number) => {
      if (version === 1) {
        // Rename darkMode to theme in version 2
        persistedState.theme = persistedState.darkMode ? 'dark' : 'light';
        delete persistedState.darkMode;
      }
      return persistedState;
    },
  }
)

Clearing Persisted State

To clear the persisted state — for example when the user logs out — call useStore.persist.clearStorage(). This removes the data from AsyncStorage. You can also call useStore.getState().reset() to clear the in-memory state at the same time. Doing both ensures the user starts fresh on the next app launch.

async function handleLogout() {
  // Clear in-memory state
  useAuthStore.getState().logout();

  // Clear persisted state from AsyncStorage
  await useAuthStore.persist.clearStorage();

  navigation.reset({ index: 0, routes: [{ name: 'Login' }] });
}

Using SecureStore for Sensitive Data

For sensitive values like auth tokens, prefer Expo SecureStore over plain AsyncStorage. SecureStore uses the device's secure enclave (iOS Keychain / Android Keystore) to encrypt data at rest. You can create a custom Zustand storage adapter using SecureStore's getItemAsync and setItemAsync methods.

import * as SecureStore from 'expo-secure-store';

const secureStorage = {
  getItem: async (name: string) => await SecureStore.getItemAsync(name),
  setItem: async (name: string, value: string) =>
    await SecureStore.setItemAsync(name, value),
  removeItem: async (name: string) =>
    await SecureStore.deleteItemAsync(name),
};

// Use secureStorage instead of AsyncStorage:
storage: createJSONStorage(() => secureStorage),

Debugging Persisted State

To inspect what is stored in AsyncStorage during development, call AsyncStorage.getAllKeys() and AsyncStorage.multiGet(keys) in the dev console or a debug screen. You can also manually clear stale persisted state with AsyncStorage.clear() when testing migration logic. Always test with a fresh install to simulate real user upgrade scenarios.

// Debug helper — call from a dev-only screen
async function printStorage() {
  const keys = await AsyncStorage.getAllKeys();
  const pairs = await AsyncStorage.multiGet(keys);
  pairs.forEach(([key, value]) => {
    console.log(key, ':', JSON.parse(value ?? 'null'));
  });
}

Persisting a Cart Store Example

Here is a realistic cart store that persists its items list across app restarts. Loading and error state are excluded from persistence using partialize. The total is derived on the fly in the component rather than stored, so it is always consistent with the items array after rehydration.

export const useCartStore = create(
  persist<CartStore>(
    (set, get) => ({
      items: [],
      addItem: (item) => set((state) => ({ items: [...state.items, item] })),
      removeItem: (id) =>
        set((state) => ({ items: state.items.filter((i) => i.id !== id) })),
      clearCart: () => set({ items: [] }),
    }),
    {
      name: 'cart-store',
      storage: createJSONStorage(() => AsyncStorage),
      partialize: (state) => ({ items: state.items }),
    }
  )
);

Quick Check

Test your understanding of React Native Mobile Development concepts from this lesson.

Lesson Recap

In this lesson you learned: the persist middleware wraps a Zustand store to save and restore state from AsyncStorage automatically, partialize controls which fields are persisted to avoid saving transient loading or error state, and version with migrate handles breaking state shape changes across app updates. Next up we explore the slices pattern and Devtools integration in Zustand.

よくある質問

「AsyncStorageによるZustand Stateの永続化」レッスンは無料ですか？

はい。「AsyncStorageによるZustand Stateの永続化」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、React Native Academyコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 React Native Academyコースには全4レッスンが含まれています。

「AsyncStorageによるZustand Stateの永続化」で何を学びますか？

AsyncStorageを基盤とするpersistミドルウェアでZustand storeをラップし、アプリを再起動してもstateが保持されるようにして、再ハイドレーションのタイミングを扱いますブラウザで直接実行するハンズオンコードでReact Native Academyを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

React Native Academyを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのReact Native Academyは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン3/4です。

「AsyncStorageによるZustand Stateの永続化」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このReact Native Academyレッスンでコードを書いて実行できますか？

はい。すべてのReact Native Academyレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

このコースのすべてのレッスン

← React Native Academyに戻る