How to Migrate User Data from Native to Cross-Platform Apps

Migrating a native mobile app to a cross‑platform framework such as Flutter or React Native can streamline development and reduce maintenance overhead. 

However, the most delicate part of such a transition isn’t the UI or business logic but migrating user data safely. Apps that store preferences, cached content, or authentication tokens locally must retain that data after the transition. This article explains how to migrate local data from native Android/iOS apps into cross‑platform solutions and how to avoid common pitfalls.

For readers new to the debate between platform‑specific and cross‑platform development, our comparison of Native vs Cross‑Platform Development offers further context on why teams choose to migrate.

Why Data Migration Matters

When users upgrade to a new cross‑platform version, they expect their settings and offline data to be preserved.

Otherwise, the update feels like a fresh install, and users may abandon the app. Data can live in different stores depending on the platform:

Type	Android (Native)	iOS (Native)
Key–value	SharedPreferences	UserDefaults
Secure data	Android Keystore	Keychain (Keychain Group)
Database	SQLite / Room	Core Data / SQLite
Temporary files	Internal storage	Documents / Cache

The goal is to transfer local user databases and key–value stores into the new cross‑platform storage mechanism without losing any records or compromising encryption.

Requirements

Before writing migration code, ensure that the new cross‑platform build can access the old app’s sandbox. This requires keeping critical identifiers and signing credentials unchanged:

iOS

• Bundle identifier: Keep the same bundle ID as the native app.
• App Group / Keychain Group: If your native app used shared storage (for example, storing credentials in a Keychain access group), reuse the same App Group identifier. For shared keychain access, all apps must belong to the same Apple Developer Team ID and use the same Keychain Access Group configuration. The Team ID is automatically included as a prefix in the access group name when provisioning the app.

Android

• Package name: Don’t change the application ID after you publish your app. If you change it, Google Play Store treats the subsequent upload as a new app.”
• Keystore: Always sign the cross-platform APK or AAB with the same app signing key used for the original native app. Users can only update your app if the update is signed with the same key; otherwise, the Play Store and the operating system will reject the update and treat it as a separate installation.

Meeting these requirements ensures the new app can read the old local storage and perform in‑place migration.

Planning the Local Storage Migration

Once identifiers and signing certificates are aligned, plan how the new cross-platform app will read and migrate data from the native layer into its own storage.

Data migration strategies vary depending on how the data was stored originally. In most cases, the new app can read existing data directly using compatible libraries or, when necessary, through a native bridge for encrypted or proprietary data.

For example:

• Databases and preferences: If your native app used SQLite, Room, SharedPreferences, or UserDefaults, the cross-platform app can often read and migrate this data directly using libraries like sqflite or react-native settings.
• Secure data: Sensitive information, such as access tokens or credentials, stored in the iOS Keychain or Android Keystore may require specialized libraries or native code. Tools like flutter_secure_storage and react-native-keychain provide secure, framework-level access to existing secure stores without exposing raw keys.
• Native bridging: In cases where data is encrypted with custom logic or stored in proprietary formats, you can create a small native bridge that exposes read/write methods to the cross-platform layer. Flutter uses MethodChannel or FlutterMethodChannel for this communication, while React Native uses native modules to expose APIs to JavaScript.

In practice, most apps combine these approaches — reading non-sensitive data directly while using secure storage APIs or native bridges for protected information.

Implementation Example

Below is a simplified migration script, written in JavaScript/TypeScript for conceptual clarity. In a real project, you would implement the native bindings and call them from Flutter or React Native.

// PSEUDOCODE: Data Migration Script

<strong>function</strong> <strong>migrateUserData</strong>() {
    // <strong>Step</strong> 1: Check <strong>if</strong> migration is needed
    <strong>if</strong> <strong>not</strong> needsMigration():
        print("No migration needed.")
        <strong>return</strong>

    print("Starting data migration...")

    // <strong>Step</strong> 2: Initialize storages
    oldStorage = initializeOldStorage()  // e.g., SQLite, Keychain
    newStorage = initializeNewStorage()  // e.g., MMKV, SharedPreferences

    // <strong>Step</strong> 3: Retrieve data from old storage
    oldData = oldStorage.getAllData()    // Returns a dictionary or key-value map

    // <strong>Step</strong> 4: Transform or map data <strong>to</strong> <strong>new</strong> format <strong>if</strong> needed
    mappedData = mapData(oldData)        // e.g., rename keys, adjust formats, etc.

    // <strong>Step</strong> 5: Save mapped data <strong>to</strong> <strong>new</strong> storage
    newStorage.saveAll(mappedData)

    // <strong>Step</strong> 6: Mark migration as complete
    setMigrationFlag(true)
    print("Migration complete!")
}Code language: HTML, XML (xml)

Run this migration logic once on the first launch after updating. If it succeeds, set a flag so it does not run again. If it fails, log the issue and retry on the next launch.

Framework‑Specific Notes

When planning the migration, it helps to map each native storage technology to its cross-platform equivalent. This makes it easier to read existing data and write it into the new storage layer with minimal custom logic.

React Native

Native Storage	Cross-Platform Library	Purpose / Notes
SharedPreferences / UserDefaults	https://reactnative.dev/docs/settings	Handles simple key–value pairs such as settings or flags.
SQLite / Room / Core Data	react-native-sqlite-storage	Accesses or migrates structured local databases.
Keychain / Keystore	react-native-keychain	Provides secure access to credentials and tokens stored in native secure storage.

If the existing data uses custom encryption or a proprietary format, create a native bridge module to expose the migration logic. React Native modules allow you to call native APIs and pass data to JavaScript for transformation or storage.

Flutter

Native Storage	Cross-Platform Library	Purpose / Notes
SharedPreferences / UserDefaults	shared_preferences	Stores lightweight key–value data such as preferences and UI states.
SQLite / Room / Core Data	sqflite	Reads and writes relational database content from the native app.
Keychain / Keystore	flutter_secure_storage	Provides encrypted, secure key–value storage through native Keychain and Keystore APIs.

If data can’t be accessed directly—such as when it’s encrypted or stored in a proprietary format—use platform channels to connect Dart and native code.

MethodChannel and FlutterMethodChannel let you call native APIs asynchronously, ensuring the UI remains responsive while the migration runs in the background.

Data Transformation and Validation

Data stored by native apps may use different keys and formats than your cross‑platform solution. Before saving data into the new storage:

• Map old keys to new names. For example, rename user_is_logged_in to isLoggedIn.
• Convert data types. Native code may store booleans as integers; convert them back as needed.
• Validate required fields. Ensure no required fields are missing or corrupted.
• Plan database schema migration. If the native app used SQLite or Core Data, design a new schema for sqflite or another package. Migrate tables and columns accordingly.

Add logging and analytics to track migration success rates and detect anomalies early.

Security and Sensitive Data

Credentials and tokens require special handling:

• Keychain / Keystore access: Use a shared Keychain group (iOS) or Keystore alias (Android) to migrate secure credentials. 
• Avoid exporting sensitive data: Never write encrypted tokens to plain text. Use in‑memory decryption and re‑encrypt before saving to the new store.
• Native helpers: If encryption keys differ between apps, implement a small native helper to decrypt data and re‑encrypt it for the cross‑platform store.

These measures are essential to migrating keychain and SharedPreferences data securely during a native‑to‑cross‑platform migration.

Testing and Rollout

Before releasing the cross‑platform update:

• Test on real devices with existing user data. Verify that preferences, tokens, and database records are preserved.
• Simulate interruptions. Force‑close the app mid‑migration to ensure that a partial migration doesn’t corrupt data.
• Measure performance. Large migrations can delay startup; perform them asynchronously and show a progress indicator if needed.
• Track metrics after release. Use analytics to monitor migration success rates and crash reports. If failure rates rise, disable the migration or roll back the update.

Common Pitfalls

• Changing the bundle or package ID: Doing so creates a new app; the OS isolates its data. Preferences and secure storage will only persist if you keep the same applicationId (Android) and bundle identifier (iOS).
• Missing secure storage access: Failing to include the correct Keychain group can prevent secure tokens from migrating.
• Blocking the main thread: Running migration synchronously delays app startup; perform heavy operations in a background thread.
• Ignoring schema changes: A mismatch between the old and new database schema can corrupt data. Always validate and transform data accordingly.

Notes on Emerging Technology

In October 2025, Apple introduced AppMigrationKit in iOS 26.1 beta, a framework designed to transfer on‑device data between iOS and non‑Apple platforms. The framework allows apps to export or import local data during device setup. Although still in beta, AppMigrationKit signals growing support for cross‑platform data migration at the OS level.

Conclusion

Migrating local data is the most delicate part of rebuilding a native app in a cross‑platform framework. With careful planning, consistent identifiers and signing credentials, accurate data mapping, robust validation and logging, and secure handling of credentials, you can preserve user data during a native‑to‑cross‑platform rebuild without losing a single record.

Done right, the migration is invisible to users: their sessions, preferences, and offline data remain exactly where they left them.

If your organization is considering a broader digital transformation, see our guide to application modernization strategy for insights on how to update legacy systems holistically.

Partner with Cheesecake Labs

Cheesecake Labs helps companies migrate native mobile apps to cross‑platform solutions such as Flutter and React Native. Our teams modernize architectures, migrate local data safely, and preserve user experience end‑to‑end. Learn more about our cross‑platform migration expertise.

FAQ