I have an app for macOS that is built using Mac Catalyst. I need to perform some background processing. I'm using BGProcessingTaskRequest to schedule the request. I have also integrated CKSyncEngine so I need that to be able to perform its normal background processing. On iOS, when the user leaves the app, I can see a log message that the request was scheduled and a bit later I see log messages coming from the actual background task code. On macOS I ran the app from Xcode. I then quit the app (Cmd-q). I can see the log message that the request was scheduled. But the actual task is never run. In my test, I ran my app on a MacBook Pro running macOS 26.0. When I quit the app, I checked the log file in the app sandbox and saw the message that the task was scheduled. About 20 minutes later I closed the lid on the MacBook Pro for the night. I did not power down, it just went to sleep. Roughly 10 hours later I opened the lid on the MacBook Pro, logged in, and checked the log file. It had not been updated since quitting the app. I should also mention that the laptop was not plugged in at all during this period. My question is, does a Mac Catalyst app support background processing after the user quits the app? If so, how is it enabled? The documentation for BGProcessingTaskRequest and BGProcessingTask show they are supported under Mac Catalyst, but I couldn't find any documentation in the Background Tasks section that mentioned anything specific to setup for Mac Catalyst. Running the Settings app and going to General -> Login Items & Extension, I do not see my app under the App Background Activity section. Does it need to be listed there? If so, what steps are needed to get it there? If this is all documented somewhere, I'd appreciate a link since I was not able to find anything specific to making this work under Mac Catalyst.

I have been using the basic NSPersistentContainer with 100k+ records for a while now with no issues. The database size can fluctuate a bit but on average it takes up about 22mb on device. When I switch the container to NSPersistentCloudKitContainer, I see a massive increase in size to ~150mb initially. As the sync engine uploads records to iCloud it has ballooned to over 600mb on device. On top of that, the user's iCloud usage in settings reports that it takes up 1.7gb in the cloud. I understand new tables are added and history tracking is enabled but the size increase seems a bit drastic. I'm not sure how we got from 22mb to 1.7gb with the exact same data. A few other things that are important to note: I import all the 100k+ records at once when testing the different containers. At the time of the initial import there is only 1 relation (an import group record) that all the records are attached to. I save the background context only once after all the records and the import group have been made and added to the context. After the initial import, some of these records may have a few new relations added to them over time. I suppose this could be causing some of the size increase, but its only about 20,000 records that are updated. None of the records include files/ large binary data. Most of the attributes are encrypted. I'm syncing to the dev iCloud environment. When I do make a change to a single attribute in a record, CloudKit reports that every attribute has been modified (not sure if this is normal or not ) Also, When syncing to a new device, the sync can take hours - days. I'm guessing it's having to sync both the new records and the changes, but it exponentially gets slower as more records are downloaded. The console will show syncing activity, but new records are being added at a slower rate as more records are added. After about 50k records, it grinds to a halt and while the console still shows sync activity, only about 100 records are added every hour. All this to say i'm very confused where these issues are coming from. I'm sure its a combination of how i've setup my code and the vast record count, record history, etc. If anyone has any ideas it would be much appreciated.

I have SwiftData models containing arrays of Codable structs that worked fine before adding CloudKit capability. I believe they are the reason I started seeing errors after enabling CloudKit. Example model: @Model final class ProtocolMedication { var times: [SchedulingTime] = [] // SchedulingTime is Codable // other properties... } After enabling CloudKit, I get this error logged to the console: 'NSKeyedUnarchiveFromData' should not be used to for un-archiving and will be removed in a future release CloudKit Console shows this times data as "plain text" instead of "bplist" format. Other struct/enum properties display correctly (I think) as "bplist" in CloudKit Console. The local SwiftData storage handled these arrays fine - this issue only appeared with CloudKit integration. What's the recommended approach for storing arrays of Codable structs in SwiftData models that sync with CloudKit?

In didFinishLaunchingWithOptions I have this setup for getting the token to send to my server for notifications. The issue is that the delegate callback didRegisterForRemoteNotificationsWithDeviceToken gets called twice when also initializing a CKSyncEngine object. This confuses me. Is this expected behavior? Why is the delegate callback only called twice when both are called, but not at all when only using CKSyncEngine. See code and comments below. /// Calling just this triggers `didRegisterForRemoteNotificationsWithDeviceToken` once. UIApplication.shared.registerForRemoteNotifications() /// When triggering the above function plus initializing a CKSyncEngine, `didRegisterForRemoteNotificationsWithDeviceToken` gets called twice. /// This somewhat make sense, because CloudKit likely also registers for remote notifications itself, but why is the delegate not triggered when *only* initializing CKSyncEngine and removing the `registerForRemoteNotifications` call above? let syncManager = SyncManager() /// Further more, if calling `registerForRemoteNotifications` with a delay instead of directly, the delegate is only called once, as expected. For some reason, the delegate is only triggered when two entities call `registerForRemoteNotifications` at the same time? DispatchQueue.main.asyncAfter(deadline: .now() + 4) { UIApplication.shared.registerForRemoteNotifications() } func application(_ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data) { print("didRegisterForRemoteNotificationsWithDeviceToken") }

My app has three main SwiftData models: Collection, SavedItem, and Extract. A Collection can contain subcollections (folders within folders) and SavedItems (files). Each SavedItem can have child Extracts. I'm preparing for the ability for users to be able to share Collections with each other. Currently, my architecture treats each Collection as the root of its own CloudKit zone (a root parent Collection and all of its items and subcollections live in 1 zone). This makes sharing and isolation straightforward, but it also means that moving a SavedItem or subcollection between Collections involves moving it across zones. I’m trying to figure out the best pattern for handling these cross-zone moves while keeping data integrity, relationships, and sharing intact. My understanding is that in CloudKit, and moving a record from Zone A to Zone B would require deleting it from Zone A and recreating it in Zone B - while somehow maintaining the link back to my local SwiftData store. Has anyone run into this or know how best I should handle it?

Hi, I'm using SwiftData in my app, and I want to sent data to iCloud with CloudKit, but I found that If the user turns off my App iCloud sync function in the settings App, the local data will also be deleted. A better way is maintaining the local data, just don't connect to iCloud.How should I do that? I need guidance!!! I'm just getting started with CloudKit And I would be appreciated!

i want to save data like images, text,amd mapviews with swiftui. It is only saved but if you delete the app of buy a new iPhone everything is deleted, how can I make if that the information saved on my app is saved even after I update the app, delete the app, or put the app in another iPhone with SwiftUI? i have watched youtube videos and im still confused,please help.

The CloudKit Console includes a Unique Users table in the Usage section. The numbers here are lower than what I would expect. Does this only track a certain percentage of users, e.g. users have opted in to share analytics with developers?

I a using the current RC version of iOS on both my iPhone and iPad. I and developing an iCloud based app and it works correctly on iOS 18. When I upgraded to iOS 26 the iCloud functions work correctly but the push notifications do not work. The issue appears to be creating subscriptions. The following code should create a subscription and does not get an error, but it did to create a subscription under iOS 26. func subscribeToNotifications(recordType: String, subscriptionID: String, notification: CKSubscription.NotificationInfo) { let subscriptionIDForType = "\(subscriptionID)-\(recordType)" let predicate = NSPredicate(value: true) let subscription = CKQuerySubscription(recordType: recordType, predicate: predicate, subscriptionID: subscriptionIDForType, options: [.firesOnRecordCreation, .firesOnRecordUpdate, .firesOnRecordDeletion]) let notification = CKSubscription.NotificationInfo() subscription.notificationInfo = notification CKContainer.default().publicCloudDatabase.save(subscription) { (returnedSubscription, error) in if let error = error { print("Error saving subscription: \(error)") } else { print("Successfully saved subscription: recordType: " + recordType + " subscriptionID: " + subscriptionIDForType) } } } Print results: Successfully saved subscription: recordType: folder subscriptionID: folderName-folder

I'm trying to handle the serverRecordChanged return code you get in CKError when you have a conflict and your using the savePolicy of ifServerRecordUnchanged. According to the CKError.Code.serverRecordChanged documentation, I should be receiving all three records that I need to do a 3-way merge. The problem is that the ancestorRecord (CKRecordChangedErrorAncestorRecordKey can also be used to look it up in the userInfo) doesn't actually contain a record. It only contains the record metadata. Is there something I need to be doing to get the full ancestorRecord in the CKError? If not is it possible to query iCloud for the ancestorRecord? Given that iCloud has the change history (as I understand it), then it is theoretically possible. I just don't know how to do it if it is possible. Are 3-way merges even possible? The design of the serverRecordChanged looks like that is the intent, but I can't see how to do it with the data that CloudKit is providing.

Hi, Not sure how to describe my issue best: I am using SwiftData and CloudKit to store my data. In the past, when I tested my app on different devices, the data would sync between the devices automatically. For whatever reason this has stopped now and the data no longer syncs. No matter what I do, it feels as if all the data is actually stored just locally on each device. How can I check if the data is actually stored in the cloud and what could be reasons, why its no longer synching between my devices (and yes, I am logged in with the same Apple ID on all devices). Thanks for any hint! Max

I have an app with SwiftData and CloudKit sync enabled, it was working fine but I recently noticed that the sync with CloudKit is not working anymore. All the changes are persisted locally just fine. When running in simulator (iOS 26/iPhone 17 Pro) I get the following error in the console: CoreData+CloudKit: -[NSCloudKitMirroringDelegate recoverFromError:](2317): <NSCloudKitMirroringDelegate: 0x600003d14c30> - Attempting recovery from error: Error Domain=NSCocoaErrorDomain Code=134421 "Export encountered an unhandled exception while analyzing history in the store." UserInfo={NSLocalizedFailureReason=Export encountered an unhandled exception while analyzing history in the store., NSUnderlyingException=-[NSEntityDescription objectID]: unrecognized selector sent to instance 0x60000351aec0} I already tried Reseting the environment back to production in CloudKit and Erasing all Contents and Settings in the simulator but I keep getting the same error. Is there something else I can do to fix this?

Hello Apple Team, We’re building a CloudKit-enabled Core Data app and would like clarification on the behavior and performance characteristics of Binary Data attributes with “Allows External Storage” enabled when used with NSPersistentCloudKitContainer. Initially, we tried storing image files manually on disk and only saving the metadata (file URLs, dimensions, etc.) in Core Data. While this approach reduced the size of the Core Data store, it introduced instability after app updates and broke sync between devices. We would prefer to use the official Apple-recommended method and have Core Data manage image storage and CloudKit syncing natively. Specifically, we’d appreciate guidance on the following: When a Binary Data attribute is marked as “Allows External Storage”, large image files are stored as separate files on device rather than inline in the SQLite store. How effective is this mechanism in keeping the Core Data store size small on device? Are there any recommended size thresholds or known limits for how many externally stored blobs can safely be managed this way? How are these externally stored files handled during CloudKit sync? Does each externally stored Binary Data attribute get mirrored to CloudKit as a CKAsset? Does external storage reduce the sync payload size or network usage, or is the full binary data still uploaded/downloaded as part of the CKAsset? Are there any bandwidth implications for users syncing via their private CloudKit database, versus developer costs in the public CloudKit database? Is there any difference in CloudKit or Core Data behavior when a Binary Data attribute is managed this way versus manually storing image URLs and handling the file separately on disk? Our goal is to store user-generated images efficiently and safely sync them via CloudKit, without incurring excessive local database bloat or CloudKit network overhead. Any detailed guidance or internal performance considerations would be greatly appreciated. Thank you, Paul Barry Founder & Lead Developer — Boat Buddy / Vessel Buddy iOS App Archipelago Environmental Solutions Inc.

I've seen a few older posts claiming the same behavior I'm seeing which is my cloudkit/core data app only syncs to iOS when the iOS app is reloaded. Can someone clarify if this is a bug, or the expected behavior. I have an iOS app which the entire purpose of it is to view synced data from MacOS, and I have a refresh button which does nothing because the data only syncs when the app is closed and reopened. Am I supposed to tell users to close and reopen the app to see fresh data? that seems like a terrible UI behavior, and I know apple does not accept this as all of their apps sync without needing to be reloaded. For example the notes app does not need to be reloaded for the MacOS -> iOS data to be synced.

Hello Apple Team, We are looking at developing an iOS feature on our current development that stores user-generated images as CKAssets in the public CloudKit database, with access control enforced by our app’s own logic (not CloudKit Sharing as that has a limit of 100 shares per device). Each story or post is a public record, and users only see content based on buddy relationships handled within the app. We’d like to confirm that this pattern is consistent with Apple’s best practices for social features. Specifically: Is it acceptable to store user-uploaded CKAssets in the public CloudKit database, as long as access visibility is enforced by the app? Are there any performance or quota limitations (e.g., storage, bandwidth, or user sync limits) that apply to CKAssets in the public database when used at scale? Would CloudKit Sharing be recommended instead, even if we don’t require user-to-user sharing invitations? For App Review, is this model (public CKAssets + app-enforced access control) compliant with Apple’s data and security expectations? Are there any caching or bandwidth optimization guidelines for handling image-heavy public CKAsset data in CloudKit? Thanks again for your time

Hi everyone, We’re currently using CKSyncEngine to sync all our locally persisted data across user devices (iOS and macOS) via iCloud. We’ve noticed something strange and reproducible: On iOS, when the CKSyncEngine is initialized with manual sync behavior, both manual calls to fetchChanges() and sendChanges() happen nearly instantly (usually within seconds). Automatic syncing is also very fast. On macOS, when the CKSyncEngine is initialized with manual sync behavior, fetchChanges() and sendChanges() are also fast and responsive. However, once CKSyncEngine is initialized with automatic syncing enabled on macOS: sendChanges() still appears to transmit changes immediately. But automatic fetching becomes significantly slower — often taking minutes to pick up changes from the cloud, even when new data is already available. Even manual calls to fetchChanges() behave as if they’re throttled or delayed, rather than performing an immediate fetch. Our questions: Is this delay in automatic (and post-automatic manual) fetch behavior on macOS expected, or possibly a bug? Are there specific macOS constraints that impact CKSyncEngine differently than on iOS? Once CKSyncEngine has been initialized in automatic mode, is fetchChanges() no longer treated as a truly manual trigger? Is there a recommended workaround to enable fast sync behavior on macOS — for example, by sticking to manual sync configuration and triggering sync using a CKSubscription-based mechanism when remote changes occur? Any guidance, clarification, or experiences from other developers (or Apple engineers) would be greatly appreciated — especially regarding maintaining parity between iOS and macOS sync performance. Thanks in advance!

Hi, I did cloudkit synchronization using swiftdata. However, synchronization does not occur automatically, and synchronization occurs intermittently only when the device is closed and opened. For confirmation, after changing the data in Device 1 (saving), when the data is fetched from Device 2, there is no change. I've heard that there's still an issue with swiftdata sync and Apple is currently troubleshooting it, is the phenomenon I'm experiencing in the current version normal?

I'm trying to set up an application using SwiftData to have a number of models backed by a local datastore that's not synced to CloudKit, and another set of models that is. I was able to achieve this previously with Core Data using multiple NSPersistentStoreDescription instances. The set up code looks something like: do { let fullSchema = Schema([ UnsyncedModel.self, SyncedModel.self, ]) let localSchema = Schema([UnsyncedModel.self]) let localConfig = ModelConfiguration(schema: localSchema, cloudKitDatabase: .none) let remoteSchema = Schema([SyncedModel.self]) let remoteConfig = ModelConfiguration(schema: remoteSchema, cloudKitDatabase: .automatic) container = try ModelContainer(for: fullSchema, configurations: localConfig, remoteConfig) } catch { fatalError("Failed to configure SwiftData container.") } However, it doesn't seem to work as expected. If I remove the synced/remote schema and configuration then everything works fine, but the moment I add in the remote schema and configuration I get various different application crashes. Some examples below: A Core Data error occurred." UserInfo={Reason=Entity named:... not found for relationship named:..., Fatal error: Failed to identify a store that can hold instances of SwiftData._KKMDBackingData<...> Has anyone ever been able to get a similar setup to work using SwiftData?

Hi all, As you know, when using SwiftData Cloudkit, all relationships are required to be optional. In my app, which is a list app, I have a model class Project that contains an array of Subproject model objects. A Subproject also contains an array of another type of model class and this chain goes on and on. In this type of pattern, it becomes really taxxing to handle the optionals the correct way, i.e. unwrap them as late as possible and display an error to the user if unable to. It seems like most developers don't even bother, they just wrap the array in a computed property that returns an empty array if nil. I'm just wondering what is the recommended way by Apple to handle these optionals. I'm not really familiar with how the CloudKit backend works, but if you have a simple list app that only saves to the users private iCloud, can I just handwave the optionals like so many do? Is it only big data apps that need to worry? Or should we always strive to handle them the correct way? If that's the case, why does it seem like most people skip over them? Be great if an Apple engineer could weigh in.

Hi everyone, I’ve been working on migrating my app (SwimTimes, which helps swimmers track their times) to use Core Data + CKSyncEngine with Swift 6. After many iterations, forum searches, and experimentation, I’ve created a focused sample project that demonstrates the architecture I’m using. The good news: 👉 I believe the crashes I was experiencing are now solved, and the sync behavior is working correctly. 👉 The demo project compiles and runs cleanly with Swift 6. However, before adopting this as the final architecture, I’d like to ask the community (and hopefully Apple engineers) to validate a few critical points, especially regarding Swift 6 concurrency and Core Data contexts. Architecture Overview Persistence layer: Persistence.swift sets up the Core Data stack with a main viewContext and a background context for CKSyncEngine. Repositories: All Core Data access is abstracted into repository classes (UsersRepository, SwimTimesRepository), with async/await methods. SyncEngine: Wraps CKSyncEngine, handles system fields, sync tokens, and bridging between Core Data entities and CloudKit records. ViewModels: Marked @MainActor, exposing @Published arrays for SwiftUI. They never touch Core Data directly, only via repositories. UI: Simple SwiftUI views bound to the ViewModels. Entities: UserEntity → represents swimmers. SwimTimeEntity → times linked to a user (1-to-many). Current Status The project works and syncs across devices. But there are two open concerns I’d like validated: Concurrency & Memory Safety Am I correctly separating viewContext (main/UI) vs. background context (used by CKSyncEngine)? Could there still be hidden risks of race conditions or memory crashes that I’m not catching? Swift 6 Sendable Compliance Currently, I still need @unchecked Sendable in the SyncEngine and repository layers. What is the recommended way to fully remove these workarounds and make the code safe under Swift 6’s stricter concurrency rules? Request Please review this sample project and confirm whether the concurrency model is correct. Suggest how I can remove the @unchecked Sendable annotations safely. Any additional code improvements or best practices would also be very welcome — the intention is to share this as a community resource. I believe once finalized, this could serve as a good reference demo for Core Data + CKSyncEngine + Swift 6, helping others migrate safely. Environment iOS 18.5 Xcode 16.4 macOS 15.6 Swift 6 Sample Project Here is the full sample project on GitHub: 👉 [https://github.com/jarnaez728/coredata-cksyncengine-swift6] Thanks a lot for your time and for any insights! Best regards, Javier Arnáez de Pedro