NSCoding Archiver vs NSDocument Restoration: Which Is Safer for Offline Data Recovery?

When an Objective‑C application is uninstalled and later re‑installed on a device that has never connected to a network, the only source of user data is the local backup archive generated by the previous installation. The developer must decide how to archive the data to guarantee that, after restoration, the object graph is intact and can be programmatically verified.

Using NSCoding with NSKeyedArchiver preserves the full object graph, but the archive is just a binary blob. It offers no automatic checksum or version stamp, and verification must be performed by the application after unarchiving. Additionally, class names are stored verbatim, so any change in the class hierarchy between the archive and the runtime can silently corrupt data unless the developer explicitly handles class policies.

Subclassing NSDocument (or UIDocument on iOS) integrates the archive with the OS backup APIs. The framework automatically encrypts the document, tracks changes, and can invoke fileWroteContents: callbacks that can be used for integrity checks. However, this approach relies on the document handling semantics of the specific SDK version, and if iCloud sync is disabled or the local cache is cleared, the framework may skip restoring the user data altogether.

Given the constraint of an offline re‑installation, the trade‑off centers on whether the application can tolerate an ad‑hoc verification process with NSCoding or whether it prefers the built‑in, but version‑sensitive, restoration logic of NSDocument. The key uncertainty is how each method behaves when class definitions evolve across minor OS updates or when the backup attribute isExcludedFromBackup is set on the archive.

Which approach offers a more reliable path to data integrity when restoring from a local archive after an offline reinstall?

How can a developer detect and handle class mismatches during NSKeyedUnarchiver without relying on explicit class policy configuration?

Does NSDocument automatically preserve a version stamp across minor OS updates, and how does that affect the ability to verify restored data?