I am using NSCollectionLayoutSection.list as follow. private func layoutConfig() -> UICollectionViewCompositionalLayout { let layout = UICollectionViewCompositionalLayout { section, layoutEnvironment in var config = UICollectionLayoutListConfiguration(appearance: .plain) config.headerMode = .supplementary config.footerMode = .none config.showsSeparators = false config.headerTopPadding = 0 // https://developer.apple.com/forums/thread/759987 let layoutSection = NSCollectionLayoutSection.list(using: config, layoutEnvironment: layoutEnvironment) layoutSection.interGroupSpacing = 0 layoutSection.contentInsets = NSDirectionalEdgeInsets(top: 0, leading: 0, bottom: 0, trailing: 0) if let header = layoutSection.boundarySupplementaryItems.first(where: { $0.elementKind == UICollectionView.elementKindSectionHeader }) { header.contentInsets = NSDirectionalEdgeInsets(top: 0, leading: 0, bottom: 0, trailing: 0) } return layoutSection } return layout } We provide our own custom header view and cell item view. Header View class HideShowHeader: UICollectionViewListCell { override func awakeFromNib() { super.awakeFromNib() // Initialization code } override func systemLayoutSizeFitting(_ targetSize: CGSize) -> CGSize { // Ensure the cell fills the width of the collection view let size = CGSize( width: targetSize.width, height: 80 ) print(">>>> size \(size)") return size } } Cell Item View class TodoCell: UICollectionViewListCell { override func awakeFromNib() { super.awakeFromNib() // Initialization code } override func systemLayoutSizeFitting(_ targetSize: CGSize) -> CGSize { // Ensure the cell fills the width of the collection view let size = CGSize( width: targetSize.width, height: 80 ) return size } } We would like to fine-tune the height of header and cell item. However, override systemLayoutSizeFitting doesn't work. May I know, when using NSCollectionLayoutSection.list, how to specific header height and cell item height? Thanks.

Hi, Currently, instead of using a real device and test account for in-app purchase testing, we are using Products.storekit with the Simulator. Our app offers a subscription plan with a 3-day free trial. We would like to simulate the following test scenarios: User cancels the subscription within the 3-day free trial period. User cancels the subscription after the 3-day free trial period. However, in Xcode, under Debug > StoreKit > Manage Transactions..., we couldn’t find an option to simulate a subscription cancellation. There is an option to refund the purchase, but we believe this is not the same as a cancellation. Do you have any idea how we can simulate these two cases using Products.storekit and the Simulator? Thanks in advance!

We offer a 3-day free trial, and our paywall clearly states that users will be charged after the trial ends. However, some users request refunds after the charge - even after fully using our app for days or even weeks. In some cases, refunds are approved despite the users having consumed our AI processing services for up to a month. Since our app relies on backend AI processing, each user session incurs a real cost. To prevent losses, we utilize RevenueCat’s CONSUMPTION_REQUEST system and have set our refundPreference to: "2. You prefer that Apple declines the refund". Until recently, Apple typically respected this preference, and 90% of refund requests were declined as intended. However, starting about a week ago, we observed a sudden reversal: Apple is now approving around 90% of refund requests, despite our refund preference. As a result, we are operating at a loss and have had to halt both our marketing campaigns and our 3-day free trial. We’re trying to understand whether this shift is due to a change in Apple’s refund policy, or if we need to handle CONSUMPTION_REQUEST differently on our end. Has anyone else experienced similar changes? Any insights would be greatly appreciated.

Apple has shown us how to perform heavy write operation using background thread (by using newBackgroundContext) in their official earth quake example - https://github.com/yccheok/earthquakes-WWDC20 But, what about heavy read operation? (millions of rows for stress test purpose) We would also like our app UI to be responsiveness, when we are launching the app for first time, and the app is reading a large amount of data from CoreData. The following is the code snippet which is using NSFetchedResultController. [UI is not responsiveness if there are a lot of rows] } [UI is not responsiveness if there are a lot of rows] We try to perform controller.performFetch() using background thread. Still, but not sure why, the UI is still not responsiveness. My guess is that, after NSFetchedResultsController is occupied UI main thread, to perform some time consuming I/O read operation. } [UI is responsive now. But the solution is incorrect...] I guess, we need to place NSFetchedresultController under background thread too. Hence, we do the following modification. } The UI is responsiveness during fetching, and data is able to be fetched and shown after some time. However, if we investigate further by using the launching argument com.apple.CoreData.ConcurrencyDebug 1 We will experience the following crash after controller.performFetch() finish executed. CoreData`+[NSManagedObjectContext __Multithreading_Violation_AllThatIsLeftToUsIsHonor__]: May I know, is it ever possible to make UI responsive, when we are using NSFetchedResultController to load a large amount of data (few millions rows as per testing)? Can NSFetchedResultController ever operated under background thread?

This problem has buzzed me quite a while. So far, I still haven't founded a good solution. Currently, I have an entity with a Bool column named pinned. I use it as the sectionNameKeyPath for NSFetchedResultsController. So, my UICollectionView will always have 1 sections (All pinned = true, or All pinned = false), or 2 sections (Some pinned = true, and some pinned = false) When I toggle the pinned value from true to false, or false to true, I expect FRC shall fire a "move" callback. (Due to item has moved to a new section) This happen most of the time. However, sometimes, randomly, instead of firing "move" callback, FRC will fire "update" callback. When such incident happen, I will exam the content of fetchedResultsController.sections. Then, I will notice the entity item stays in wrong section. My FRC looks pretty straightforward. lazy var fetchedResultsController: NSFetchedResultsControllerNSPlainNote = { // Create a fetch request for the Quake entity sorted by time. let fetchRequest = NSFetchRequestNSPlainNote(entityName: "NSPlainNote") fetchRequest.sortDescriptors = [ NSSortDescriptor(key: "pinned", ascending: false) ] // Create a fetched results controller and set its fetch request, context, and delegate. let controller = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: CoreDataStack.INSTANCE.persistentContainer.viewContext, sectionNameKeyPath: "pinned", cacheName: nil ) controller.delegate = fetchedResultsControllerDelegate // Perform the fetch. do { try controller.performFetch() } catch { fatalError("Unresolved error \(error)") } return controller }() This is how I update the pinned column using background thread. func updatePinned(_ objectID: NSManagedObjectID, _ pinned: Bool) { let coreDataStack = CoreDataStack.INSTANCE let backgroundContext = coreDataStack.backgroundContext backgroundContext.perform { let nsPlainNote = try! backgroundContext.existingObject(with: objectID) as! NSPlainNote nsPlainNote.pinned = pinned RepositoryUtils.saveContextIfPossible(backgroundContext) } } I am not really sure, whether this can caused by my background thread. As, if I replace the backgroundContext with viewContext, I haven't observed the random problem so far. But, even so, I am not confident to conclude using backgroundContext is the culprit to this problem. The setup of my background thread is also pretty straightforward. I cannot see how it can went wrong. class CoreDataStack { public static let INSTANCE = CoreDataStack() private init() { } lazy var persistentContainer: NSPersistentContainer = { let container = NSPersistentContainer(name: "xxx") container.loadPersistentStores(completionHandler: { (storeDescription, error) in if let error = error as NSError? { fatalError("Unresolved error \(error), \(error.userInfo)") } }) // TODO: container.viewContext.automaticallyMergesChangesFromParent = true //container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy //container.viewContext.undoManager = nil //container.viewContext.shouldDeleteInaccessibleFaults = true return container }() lazy var backgroundContext: NSManagedObjectContext = { let backgroundContext = persistentContainer.newBackgroundContext() // TODO: //backgroundContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy //backgroundContext.undoManager = nil return backgroundContext }() } I was wondering, have anyone of you encounter similar problem when trying to utilize sectionNameKeyPath or FRC? Do you know what? Do you have any workaround/ solution for that? Thank you!

The following simple function will cause Xcode 12E262 to have "Abort: trap 6" during compilation. import UIKit import CoreData class ViewController: UIViewController {     func xyz() {         let container = NSPersistentContainer(name: "xyz")         let batchUpdateRequest = NSBatchUpdateRequest(entityName: "xyz")         let batchUpdateResult = try! container.viewContext.execute(batchUpdateRequest) as? NSBatchUpdateResult         guard let batchUpdateResult = batchUpdateResult else { return }     }     override func viewDidLoad() {         super.viewDidLoad()         // Do any additional setup after loading the view.     } } We will not observe "Abort: trap 6", if under Build Settings, we are using "Optimize for Speed" in Debug, instead of "No Optimization" We can also avoid "Abort: trap 6", if we change the following code guard let batchUpdateResult = batchUpdateResult else { return } to guard let batchUpdateResult2 = batchUpdateResult else { return } May I know, why is it so? A simpler code example to reproduce problem, without CoreData would be import UIKit class ViewController: UIViewController {     func getAny() throws -> Any? {         return nil     }     func xyz() {         let name = try! getAny() as? UIViewController         guard let name = name else { return }     }     override func viewDidLoad() {         super.viewDidLoad()         // Do any additional setup after loading the view.     } }

Introduction I expect when I perform "update" on 1 of the CoreData entity content, corresponding UICollectionViewCell should updated seamlessly. But, the thing doesn't work as expected. After debugging, I notice that instead of updating visible UICollectionViewCell on screen, an invisible offscreen UICollectionViewCell has been created and all update operations are performed on the invisible UICollectionViewCell?! Simple hookup between NSFetchedResultsController and Diffable Data Source The hookup is pretty straightforward extension ViewController: NSFetchedResultsControllerDelegate { func controller(_ fetchedResultsController: NSFetchedResultsController<NSFetchRequestResult>, didChangeContentWith snapshotReference: NSDiffableDataSourceSnapshotReference) { guard let dataSource = self.dataSource else { return } let snapshot = snapshotReference as NSDiffableDataSourceSnapshot<Int, NSManagedObjectID> print("dataSource.apply") dataSource.apply(snapshot, animatingDifferences: true) { } } } Simple data structure import Foundation import CoreData extension NSTabInfo { @nonobjc public class func fetchRequest() -> NSFetchRequest<NSTabInfo> { return NSFetchRequest<NSTabInfo>(entityName: "NSTabInfo") } @NSManaged public var name: String? @NSManaged public var order: Int64 } extension NSTabInfo : Identifiable { } Simple data source to update cell private func initDataSource() { let dataSource = DataSource( collectionView: collectionView, cellProvider: { [weak self] (collectionView, indexPath, objectID) -> UICollectionViewCell? in guard let self = self else { return nil } guard let cell = collectionView.dequeueReusableCell( withReuseIdentifier: "cell", for: indexPath) as? CollectionViewCell else { return nil } guard let nsTabInfo = self.getNSTabInfo(indexPath) else { return nil } cell.label.text = nsTabInfo.name print("Memory for cell \(Unmanaged.passUnretained(cell).toOpaque())") print("Content for cell \(cell.label.text)\n") return cell } ) self.dataSource = dataSource } Updating code doesn't work We perform update on the 1st cell using the following code @IBAction func updateClicked(_ sender: Any) { let backgroundContext = self.backgroundContext backgroundContext.perform { let fetchRequest = NSFetchRequest<NSTabInfo>(entityName: "NSTabInfo") fetchRequest.sortDescriptors = [ NSSortDescriptor(key: "order", ascending: true) ] do { let nsTabInfos = try fetchRequest.execute() if !nsTabInfos.isEmpty { // Perform update on the first cell nsTabInfos[0].name = "\(Int(nsTabInfos[0].name!)! + 1)" if backgroundContext.hasChanges { try backgroundContext.save() } } } catch { print("\(error)") } } } Nothing is changed on the screen. However, if we look at the print output. We can see the initial content ("0") of the 1st cell is updated to "1". But, all of these are being done in an invisible same instance cell. dataSource.apply Memory for cell 0x0000000138705cd0 Content for cell Optional("1") Memory for cell 0x0000000138705cd0 Content for cell Optional("1") Memory for cell 0x0000000138705cd0 Content for cell Optional("2") Memory for cell 0x0000000138705cd0 Content for cell Optional("3") Ordering work without issue Changing the ordering of the cell works as expected. The following is the code for charging ordering. @IBAction func moveClicked(_ sender: Any) { let backgroundContext = self.backgroundContext backgroundContext.perform { let fetchRequest = NSFetchRequest<NSTabInfo>(entityName: "NSTabInfo") fetchRequest.sortDescriptors = [ NSSortDescriptor(key: "order", ascending: true) ] do { let nsTabInfos = try fetchRequest.execute() for (index, element) in nsTabInfos.reversed().enumerated() { element.order = Int64(index) } if backgroundContext.hasChanges { try backgroundContext.save() } } catch { print("\(error)") } } } Do you have idea why such problem occur? I prefer not to have collectionView.reloadData as workaround, as it will create more issue (like resetting scroll position, cell press state, ...) I posted a complete demo at https://github.com/yccheok/problem-update-frc-diffable Thank you

Currently, I have the following core data backed collection view, which enable users to perform add/ delete/ modify/ reordering. It will be much more convenient to achieve what I, if I let UICollectionViewCell, to hold its corresponding NSManagedObject. So that I can each perform add/ delete/ modify/ reordering. I was wondering, should I mark the NSManagedObject as weak, to avoid from interferencing with how CoreData manage its memory? Using weak class TabInfoSettingsCell: UICollectionViewCell { // NSManagedObject. Use weak, as we do not want to inteference with how CoreData manage its memory. private weak var nsTabInfo : NSTabInfo? Use strong Or, such concern is invalid. We can simply use strong class TabInfoSettingsCell: UICollectionViewCell { // NSManagedObject. private var nsTabInfo : NSTabInfo? Use struct Or, such concern is valid and using weak is unsafe (as it can become nil in some edge case?). We can use a struct, which contains everything including objectID, but excluding NSManagedObjectContext. class TabInfoSettingsCell: UICollectionViewCell { // struct. Contains everything including objectID, but excluding NSManagedObjectContext. private var tabInfo : TabInfo? This come with the cost of having to create a struct out from NSManagedObject each time, in cellForItemAt. func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell { ... tabInfoSettingsCell.update(nsTabInfo.toTabInfo()) ... } May I know, which is the correct design, as far as safe memory management is concerned?

NSAsynchronousFetchRequest seems like an answer to read large amount of data from CoreData, without blocking main thread. But, it is lacking some key features, provided by NSFetchedResultsController. The key features are :- In NSFetchedResultsControllerDelegate didChange and controllerDidChangeContent, we automatically receive a complete change information of persistence store. This enables us to implement the animation of add/delete/move/modify in collection view. Always listen to DB changes. Whenever there is changes being written into the persistence store, NSFetchedResultsControllerDelegate didChange and controllerDidChangeContent will be triggered automatically. This enables us to ensure our UI is in sync with DB. But, NSAsynchronousFetchRequest doesn't come with NSAsynchronousFetchedResultsController :( I was wondering, if you were using NSAsynchronousFetchRequest, how do you implement Animation changes on collection view? Always listen to DB change? My initial thought for animation changes on collection view, it seems we can utilise UICollectionViewDiffableDataSource. But, I notice it might be highly memory inefficient to do so. We need to keep ALL NSManagedObject in memory, fire all faults during comparison. It looks like we will run out of memory, if there are many rows. May I know, how do you achieve the following features, if you ever apply NSAsynchronousFetchRequest in production app? Animation changes on collection view? Always listen to DB change? Thanks.

Since StoreKit2 Transaction.currentEntitlements will able to return us user current owned purchased, during app startup. If that is the case, is it still necessary for developer to provide a restore button? If we still need to provide a restore button, what should the restore button do and what API should it call? Thanks

We start a voice recording via self.avAudioRecorder = try AVAudioRecorder( url: self.recordingFileUrl, settings: settings ) self.avAudioRecorder.record() At certain point, we will stop the recording via self.avAudioRecorder.stop() I was wondering, is it safe to perform file copy on self.recordingFileUrl immediately, after self.avAudioRecorder.stop()? Is all recording data has been flushed to self.recordingFileUrl and self.recordingFileUrl file is closed properly?

My users will redeem promo code via app store (outside my app) Currently, I am using StoreKit2 to Query Transaction.currentEntitlements during app startup Keep listening to Transaction.updates I was wondering, is that is so, is there any special code required, to handle Promo code redeem from user? I guess by keep listening to Transaction.updates, will able to handle such case? But, I am not able to test that, without rolling out my app to production. Thanks.

My XCode 13+ was used at MacBook Pro (13-inch, M1, 2020, 16G RAM) without issue Even since updated XCode to 14 week ago, I experience slowness while typing in XCode, and other editing operation. and, this crash happens few times a day Does anyone experience the same thing as I do? Thanks.

In main app, I can override dark/ light theme based on user preference, so that I can retrieve correct color information based on named color. if (user preference) { overrideUserInterfaceStyle = .light } else { overrideUserInterfaceStyle = .dark } // Dark theme/ light theme automatic aware color. SwiftUI.Color("purpleColor") However, how can I override the theme of a WidgetKit, so that my WidgetKit can interpret named color correctly? I know in WidgetKit, I can read what is current system wide theme settings using  @Environment(\.colorScheme) But, that is not what I want. I want the ability to override theme of a WidgetKit based on user preference, then able to retrieve correct named color. Thanks.

We would like to know, whether a user system locale is using 12-hours or 24-hours format? There are many proposed solutions at https://stackoverflow.com/q/1929958/72437 One of the solutions are let formatString = DateFormatter.dateFormat(fromTemplate: "j", options: 0, locale: Locale.current)! let hasAMPM = formatString.contains("a") However, to me, this is not a correct solution. When I tested with de_DE (German is using 24-hours), the returned string is HH 'Uhr' What is Uhr mean for? I guess it mean "clock" in German? There are so many other locales and one of them might contain letter a. Does anyone know, what is a correct way, to check whether user system locale is using 12-hours or 24-hours format?