React Native Storage Manager

This skill provides established patterns for data persistence using MMKV and Expo SecureStore in the Fitness Tracker App.

When to Use This Skill

Use this skill when you need to:

• Persist data locally on the device
• Implement encrypted storage for sensitive data
• Handle user preferences or application state persistence
• Manage MMKV storage instances and keys
• Perform common CRUD operations on local storage

Storage Initialization

The app uses an encrypted MMKV instance initialized in app/utils/storage/index.ts.

Secure Encryption Key

We use Expo SecureStore to persist the encryption key securely.

import * as SecureStore from "expo-secure-store"
import { MMKV } from "react-native-mmkv"

export const storage = new MMKV({
  id: "purrsuit-storage",
  encryptionKey: SecureStore.getItem("mmkv-encryption-key"),
})

Basic CRUD Operations

Use the provided helper functions from @/utils/storage.

Saving Data

import { save, saveString } from "@/utils/storage"

save("user_preferences", { theme: "dark", notifications: true })
saveString("auth_token", "secure-token-here")

Loading Data

import { load, loadString } from "@/utils/storage"

const prefs = load<{ theme: string }>("user_preferences")
const token = loadString("auth_token")

Removing Data

import { remove, clear } from "@/utils/storage"

remove("auth_token")
clear() // Clear all data

Advanced Patterns

Typed Storage Keys

Centralize storage keys to avoid typos and ensure consistency.

// app/utils/storage/keys.ts
export const STORAGE_KEYS = {
  USER_PREFS: "user_preferences",
  AUTH_TOKEN: "auth_token",
  ENCOUNTERS_CACHE: "workouts_cache",
} as const

Integration with MST

Stores can automatically persist their state using onSnapshot or by loading data during afterCreate.

References

See STORAGE_PATTERNS.md for detailed implementation examples.

See SECURITY_AND_ENCRYPTION.md for encryption best practices.