Building Offline-First iOS Applications with Local Data Storage

Offline-first behavior on iOS is not a cache toggle. It is a persistence decision that makes the device store the place where screens read, edits land, and state survives launch interruptions, suspension, and connectivity loss. Apple describes Core Data as a framework for saving permanent data for offline use on a single device, while SwiftData organizes persistent models around a ModelContainer and ModelContext that manage storage and lifecycle.