How do the Contacts, EventKit and Photos frameworks gate access, and how should an app handle limited or write-only access?

All three frameworks follow the same pattern: an authorization status you check, a request call that shows the system prompt once, an Info.plist usage description that is shown in that prompt (a missing key crashes the app when the request is made), and increasingly a narrower grant than “everything”. Contacts (CNContactStore): requestAccess(for: .contacts); the status starts at notDetermined; you fetch with unifiedContacts(matching:keysToFetch:), and must name every key you will read, otherwise accessing an unfetched property throws. Format names with CNContactFormatter (a contact with given name Asha and family name Rao formats as Asha Rao, with the locale’s ordering). iOS 18 adds a limited access mode. For picking one or a few people, use the out-of-process CNContactPickerViewController (or ContactAccessButton), which needs no permission at all. EventKit (EKEventStore): since iOS 17 the status has separate levels: writeOnly (4: can add events but not read any) and fullAccess (3), requested with requestWriteOnlyAccessToEvents or requestFullAccessToEvents. If you only add an event, use write-only or the out-of-process EKEventEditViewController, which also needs no permission. Photos (PHPhotoLibrary): requestAuthorization(for: .readWrite), with a limited status (4: the user selected specific photos) in addition to authorized (3) and denied; .addOnly suffices for saving. The out-of-process PHPickerViewController (and SwiftUI PhotosPicker) lets the user pick photos with no permission prompt and returns only what they chose.

The design principle: prefer the system picker to broad authorization. It is safer for the user, nothing to explain, no denied state to design for, and App Review looks favourably on it. When you do need the full library or address book, explain why before asking, support the limited state (show the subset, and offer a way to expand the selection: presentLimitedLibraryPicker), and never gate unrelated features behind access. Handle changes: the user can revoke permission in Settings at any time, so check the status each time you need the data, and observe PHPhotoLibraryChangeObserver or CNContactStoreDidChange and the EventKit change notification to refresh. Treat what you read as sensitive: do not upload address books or photos wholesale, do not log them, store only what you need, and declare the collection in your privacy manifest and App Store privacy labels. Request access at the moment the feature is used, not at launch.