การคงแคชคำค้นด้วย AsyncStorage

By default the React Query cache exists only in memory. When the app is closed and reopened, all cached data is gone — the user sees loading spinners while data refetches from the network. On slow or absent connections, this means a blank screen.

Cache persistence saves the React Query cache to disk (AsyncStorage on React Native) so data is available immediately on the next app launch, before any network requests complete. This is the foundation of offline-first mobile applications.

Cache persistence requires three packages: @tanstack/react-query (core), @tanstack/react-query-persist-client (the persistence adapter), and a persister implementation. For React Native we use @tanstack/async-storage-persister which wraps AsyncStorage as the persistence backend.

AsyncStorage is the standard key-value store for React Native, provided by @react-native-async-storage/async-storage. The persister serializes the entire query cache to JSON and writes it to a single AsyncStorage key.

Create a persister instance with createAsyncStoragePersister, passing the AsyncStorage instance and a storage key name. The persister serializes the React Query cache to JSON and writes it to that key whenever the cache changes.

The persister also has a throttleTime option (default 1000ms) that prevents writing to AsyncStorage too frequently during rapid state changes. Increase it if you notice excessive I/O or battery drain.

Replace the standard QueryClientProvider with PersistQueryClientProvider. Pass both the client (your QueryClient) and persistOptions (containing the persister). The provider handles restoring the cache on startup and saving it on changes automatically.

During restoration, the component tree is rendered with the cached data immediately — no loading state on first paint. React Query also schedules a background refetch to get fresh data from the server.

The persisted cache can become outdated over time. Configure maxAge in persistOptions to set how long persisted data is considered valid. Older data is discarded and fresh data is fetched from the network on next launch. The default maxAge is 24 hours.

Choose maxAge based on how quickly your data changes. For user profile data that rarely changes, 7 days might be appropriate. For news feeds that change constantly, 30 minutes keeps the cache useful without serving very stale content.

When you release a new app version with changed data structures, the old cached format may be incompatible. The buster option in persistOptions is a version string — when it changes, the old persisted cache is discarded and a fresh fetch begins.

Update the buster string whenever you make breaking changes to your API responses or query key structure. A common pattern is to use the app version number from expo-constants or a manually managed version string.

Cache restoration from AsyncStorage is asynchronous. During this brief period (usually milliseconds) the app might flash with empty data before the cache is restored. PersistQueryClientProvider provides an onSuccess callback that fires when rehydration completes.

Show a splash screen or skeleton UI until rehydration is done, then reveal the app. This prevents the jarring empty-to-full transition that happens if you render before the cache is ready.

Not all queries should be persisted. Sensitive data (user payment info), session-specific data, or very large datasets may not be appropriate to save to local storage. Use the gcTime: 0 option to exclude specific queries from persistence — they are garbage collected immediately when unmounted and never written to disk.

Alternatively, configure a custom dehydrateState function in persistOptions to filter which queries are included in the persisted snapshot.

With cache persistence enabled, users who open the app offline see cached data immediately — no loading state, no empty lists. React Query knows the data might be stale and schedules a network refetch, but it displays the cache while waiting for the connection.

Configure networkMode: 'offlineFirst' on queries that should work offline. The default mode pauses queries when offline; offlineFirst returns cached data even when offline without throwing an error.

AsyncStorage has size limits (typically 6MB per key on iOS, varies by device on Android). Persisting a large React Query cache with many queries can approach these limits. Monitor cache size using serialized length: JSON.stringify(dehydratedState).length.

Strategies to manage cache size: reduce gcTime so unused queries are garbage collected quickly before serialization, limit the number of cached items per list (use pages in infinite queries), and exclude large binary or image data from cache.

A complete offline-first setup combines cache persistence with network status detection. Use a network status hook to detect connectivity changes, and use React Query's onlineManager to notify the library when the device goes online/offline. This prevents background refetches while offline and triggers them when connectivity returns.

This combination gives users a seamless experience: app opens with cached data, shows a subtle offline indicator when disconnected, and silently refreshes when connectivity returns.

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

In this lesson you learned: PersistQueryClientProvider with createAsyncStoragePersister saves the entire React Query cache to AsyncStorage for offline-first behavior, buster invalidates stale cache formats when you ship API changes, and gcTime: 0 on individual queries excludes sensitive data from being persisted to local storage. Next up we configure staleTime, background refetch, and network reconnect behavior for a polished offline experience.