Limits of rememberSaveable Across Android Auto Backup Restore

Answer

When an app is restored via Android Auto Backup, rememberSaveable state is not recovered. The backup process includes only files, SharedPreferences, and SQLite databases; the SavedStateRegistry bundle that backs rememberSaveable is omitted. Consequently, any counter, scroll position, or form input kept only with rememberSaveable resets to its initial value after a reinstall.

Confirmed Facts

• Auto Backup serialises android:backup file system entries, SharedPreferences, and SQLite databases.
• The Bundle used by SavedStateRegistry is stored in memory and never written to disk during backup.
• After a restore, the app receives an empty onRestoreInstanceState bundle; rememberSaveable values are initialised again.
• State stored in a ViewModel that writes to SavedStateHandle can survive if the SavedStateHandle is backed by a SavedStateRegistry that writes to disk (e.g., via SavedStateViewModelFactory), but this is not the default behaviour for rememberSaveable alone.

Typical Work‑Arounds

1. Persist the value manually. Use a Saver that writes to DataStore or SharedPreferences on every change and reads it back in rememberSaveable’s initialValue lambda.
2. Use ViewModel + SavedStateHandle. Store UI‑critical data in a ViewModel that writes to SavedStateHandle, which can be backed by a file if you initialise the factory with a SavedStateRegistry that persists to disk.
3. Hybrid approach. Keep rememberSaveable for fast in‑app restoration and trigger a background sync to persistent storage on a regular interval or when the counter exceeds a threshold.

Because the backup timing occurs while the app is stopped, a custom Saver that writes to persistent storage before the backup starts will survive. The only caveat is that the app must write the value *before* the backup is triggered; otherwise the value could be lost if the app is killed between state change and backup.

Differences Between Auto Backup & ADB Restore

• adb backup can include the entire app data directory, which may contain a SavedStateRegistry snapshot if you manually serialise it. Auto Backup never does this.
• ADB restore runs in the same process state as a fresh install, so rememberSaveable behaves the same as after Auto Backup: it is empty.

Verification Checklist

1. Enable Auto Backup on the test device.
2. Open the app, change a rememberSaveable value (e.g., increment a counter).
3. Trigger a backup via Settings → Backup.
4. Uninstall the app, then reinstall and restore from backup.
5. Verify the counter has reset to its initial value.
6. Check Logcat for onRestoreInstanceState calls and confirm the bundle is empty.

Missing Diagnostic Detail

To fine‑tune the recommendation, could you confirm whether your app already writes rememberSaveable data to a persistent store (e.g., DataStore) on every change?