I was wondering, when you use CoreData, do you usually create another equivalent struct based data class, to compliment the NSManagedObject? The struct based data class, will act as the bridge, between UI layer, and CoreData data layer. For instance, I have the following CoreData model data class. @objc(NSTabInfo) public class NSTabInfo: NSManagedObject { } extension NSTabInfo { @nonobjc public class func fetchRequest() -> NSFetchRequest<NSTabInfo> { return NSFetchRequest<NSTabInfo>(entityName: "NSTabInfo") } @NSManaged public var colorIndex: Int32 @NSManaged public var customColor: Int32 @NSManaged public var name: String? @NSManaged public var order: Int64 @NSManaged public var typeValue: Int32 @NSManaged public var syncedTimestamp: Int64 @NSManaged public var uuid: UUID } extension NSTabInfo : Identifiable { } We need a UI, to represent such model data object. Initially, we have the following UI class class TabInfoCell: UICollectionViewCell { private var tabInfo: NSTabInfo? func update(_ tabInfo: NSTabInfo) { self.tabInfo = tabInfo } } But, we just feel not comfortable with such design. Letting TabInfoCell (UI class) to hold NSTabInfo (CoreData model data class) doesn't feel right, as NSTabInfo contains CoreData's context. I do not feel comfortable, to expose CoreData's context to an UI. Will holding a class reference to NSTabInfo in UI, affect CoreData memory allocation/ deallocation strategy? Using weak reference might solve the issue. But, what should the UI do when the weak reference become nil? With such concern, We have the following design struct TabInfo { enum Kind: Int { case All = 0 case Calendar case Custom case Settings } let kind: Kind var name: String? var colorIndex: Int var customColor: Int var order: Int var syncedTimestamp: Int64 var uuid: UUID } @objc(NSTabInfo) public class NSTabInfo: NSManagedObject { convenience init(context: NSManagedObjectContext, tabInfo: TabInfo) { self.init(context: context) self.colorIndex = Int32(tabInfo.colorIndex) self.customColor = Int32(tabInfo.customColor) self.name = tabInfo.name self.order = Int64(tabInfo.order) self.typeValue = Int32(tabInfo.kind.rawValue) self.syncedTimestamp = tabInfo.syncedTimestamp self.uuid = tabInfo.uuid } func toTabInfo() -> TabInfo { return TabInfo( kind: TabInfo.Kind(rawValue: Int(self.typeValue))!, name: self.name, colorIndex: Int(self.colorIndex), customColor: Int(self.customColor), order: Int(self.order), syncedTimestamp: self.syncedTimestamp, uuid: uuid ) } } @nonobjc public class func fetchRequest() -> NSFetchRequest<NSTabInfo> { return NSFetchRequest<NSTabInfo>(entityName: "NSTabInfo") } @NSManaged public var colorIndex: Int32 @NSManaged public var customColor: Int32 @NSManaged public var name: String? @NSManaged public var order: Int64 @NSManaged public var typeValue: Int32 @NSManaged public var syncedTimestamp: Int64 @NSManaged public var uuid: UUID } extension NSTabInfo : Identifiable { } Then, in our UI class, it looks like class TabInfoCell: UICollectionViewCell { private var tabInfo: TabInfo? func update(_ tabInfo: TabInfo) { self.tabInfo = tabInfo } } I was wondering, does such design philosophy make sense? Do you usually have a struct based data class, as the bridge between your UI layer, and the CoreData data layer? Thanks.

I was wondering did anyone of you come across this strange situation? I tried to index a property in entity. For instance, for entity named NSPlainNote, I try to create an index named index_plain_note_label, on property label. This is how it looks like. However, if I inspect the content of the generated SQLite file. It seems that 2 same indices with different name are created. CREATE INDEX Z_NSPlainNote_index_plain_note_label ON ZNSPLAINNOTE (ZLABEL COLLATE BINARY ASC) CREATE INDEX Z_NSPlainNote_label ON ZNSPLAINNOTE (ZLABEL COLLATE BINARY ASC) If we observe carefully, such duplication also happen in all other index with 1 property like NSPlainNote's order NSPlainNote's sticky NSTabInfo's order Such duplication does not happen on index with 2 properties, or index with unique constraint. May I know why it is so? Is there any step which I have done incorrectly?

So far, here's are the code snippets that almost work for NSFetchedResultsController + UICollectionView, based on the information provided https://developer.apple.com/videos/play/wwdc2018/225 (Starting at 36:50) https://stackoverflow.com/questions/38597804/how-to-order-moves-inserts-deletes-and-updates-in-a-uicollectionview-performb/53271562#53271562 Please note that, there are 2 [BlockOperation], as reloadItems and moveItem doesn't play well within single performBatchUpdates. Based on the workaround proposed in the video, we have to call reloadItems in a separate performBatchUpdates. We also do not follow 100% methods (Perform reloadItems typed performBatchUpdates first, followed by insert/ move/ delete typed performBatchUpdates) proposed in the video. This is because we notice that it doesn't work well even for simple case. Some strange behaviour including reloadItems will cause duplicated cell UI to be shown on screen. The "almost" work method we found are Perform performBatchUpdates for insert, move and delete At completion handler of performBatchUpdates, perform another performBatchUpdates for reloadItems NSFetchedResultsController + UICollectionView integration private var blockOperations: [BlockOperation] = [] // reloadItems and moveItem do not play well together. We are using the following workaround proposed at // https://developer.apple.com/videos/play/wwdc2018/225/ private var blockUpdateOperations: [BlockOperation] = [] extension DashboardViewController: NSFetchedResultsControllerDelegate { func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) { if type == NSFetchedResultsChangeType.insert { print(">> insert") blockOperations.append( BlockOperation(block: { [weak self] in if let self = self { self.collectionView!.insertItems(at: [newIndexPath!]) } }) ) } else if type == NSFetchedResultsChangeType.update { print(">> update") blockUpdateOperations.append( BlockOperation(block: { [weak self] in if let self = self, let indexPath = indexPath { self.collectionView.reloadItems(at: [indexPath]) } }) ) } else if type == NSFetchedResultsChangeType.move { print(">> move") blockOperations.append( BlockOperation(block: { [weak self] in if let self = self, let newIndexPath = newIndexPath, let indexPath = indexPath { self.collectionView.moveItem(at: indexPath, to: newIndexPath) } }) ) } else if type == NSFetchedResultsChangeType.delete { print(">> delete") blockOperations.append( BlockOperation(block: { [weak self] in if let self = self { self.collectionView!.deleteItems(at: [indexPath!]) } }) ) } } func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange sectionInfo: NSFetchedResultsSectionInfo, atSectionIndex sectionIndex: Int, for type: NSFetchedResultsChangeType) { if type == NSFetchedResultsChangeType.insert { print(">> section insert") blockOperations.append( BlockOperation(block: { [weak self] in if let self = self { self.collectionView!.insertSections(IndexSet(integer: sectionIndex)) } }) ) } else if type == NSFetchedResultsChangeType.update { print(">> section update") blockOperations.append( BlockOperation(block: { [weak self] in if let self = self { self.collectionView!.reloadSections(IndexSet(integer: sectionIndex)) } }) ) } else if type == NSFetchedResultsChangeType.delete { print(">> section delete") blockOperations.append( BlockOperation(block: { [weak self] in if let self = self { self.collectionView!.deleteSections(IndexSet(integer: sectionIndex)) } }) ) } } func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) { if blockOperations.isEmpty { performBatchUpdatesForUpdateOperations() } else { collectionView.performBatchUpdates({ [weak self] () -> Void in guard let self = self else { return } for operation: BlockOperation in self.blockOperations { operation.start() } self.blockOperations.removeAll(keepingCapacity: false) }, completion: { [weak self] (finished) -> Void in print("blockOperations completed") guard let self = self else { return } self.performBatchUpdatesForUpdateOperations() }) } } private func performBatchUpdatesForUpdateOperations() { if blockUpdateOperations.isEmpty { return } collectionView.performBatchUpdates({ [weak self] () -> Void in guard let self = self else { return } for operation: BlockOperation in self.blockUpdateOperations { operation.start() } self.blockUpdateOperations.removeAll(keepingCapacity: false) }, completion: { [weak self] (finished) -> Void in print("blockUpdateOperations completed") guard let self = self else { return } }) } } The above way, works "almost" well when no "section" operations involved. If there is item moved operation between different section, the following logging will be printed blockOperations completed >> move blockOperations completed >> move blockOperations completed However, if there are item being moved and section being added/ removed, the following logging will be printed >> section delete >> move >> section insert >> move This means the completion handler block is not executed! Does anyone know why it is so, and how I can workaround with this issue? Thanks.

Currently, I am porting several SQLite statement to CoreData. "SELECT id, \"order\" FROM plain_note WHERE archived = :archived AND trashed = :trashed " + "ORDER BY " + "CASE WHEN color_index = -1 THEN 12 + ABS(custom_color) ELSE " + "color_index END DESC, " + "\"order\" ASC" "SELECT id, \"order\" FROM plain_note WHERE archived = :archived AND trashed = :trashed " + "ORDER BY " + "title COLLATE NOCASE DESC, " + "CASE WHEN locked = 1 THEN NULL ELSE " + "CASE WHEN type = 0 THEN body ELSE searched_string END " + "END COLLATE NOCASE DESC, " + "\"order\" ASC" But, I am clueless on how I can make CoreData have the following CASE WHEN...END behavior, during sorting. CASE WHEN color_index = -1 THEN 12 + ABS(custom_color) ELSE color_index END DESC CASE WHEN locked = 1 THEN NULL ELSE CASE WHEN type = 0 THEN body ELSE searched_string END END COLLATE NOCASE DESC I was wondering, is there any possible technique I can use, so that NSSortDescriptor can have the similar behavior?

Currently, we try to place multiple UITextViews in UICollectionView. To ensure UICollectionView's cell height, will adjust based on the dynamic content of UITextView, this is what we have done. Disable scrolling in UITextView. Use .estimated(CGFloat(44)) for UICollectionViewCompositionalLayout Whenever there is text change, call collectionView.collectionViewLayout.invalidateLayout(). This is a critical step to ensure cell height will adjust accordingly. However, calling collectionView.collectionViewLayout.invalidateLayout() does come with a side effect. The current scroll position of UICollectionView will be reset, after calling collectionView.collectionViewLayout.invalidateLayout(). Does anyone know how can I Prevent unwanted auto scroll position resetting? UICollectionView will auto scroll to current cursor position, so that what is current being typed is visible to user? The code to demonstrate this problem is as follow - https://github.com/yccheok/checklist-demo Here's the code snippet, on what was happening as typing goes on func textViewDidChange(_ checklistCell: ChecklistCell) { // // Critical code to ensure cell will resize based on cell content. // // (But comes with a side effect which will reset scroll position.) self.collectionView.collectionViewLayout.invalidateLayout() // // Ensure our checklists data structure in sync with UI state. // guard let indexPath = collectionView.indexPath(for: checklistCell) else { return } let item = indexPath.item let text = checklistCell.textView.text self.checklists[item].text = text } Side Note Note, the closest solution we have came across is posted at https://medium.com/@georgetsifrikas/embedding-uitextview-inside-uitableviewcell-9a28794daf01 In UITableViewController, during text change, the author is using DispatchQueue.main.async { tableView?.beginUpdates() tableView?.endUpdates() } It works well. But, what is the equivalent solution for UICollectionView? We can't try out with self.collectionView.performBatchUpdates, as our solution is built around Diffable Data Source. I have tried DispatchQueue.main.async { self.collectionView.collectionViewLayout.invalidateLayout() } That doesn't solve the problem either. Thank you.

I have the following top status bar hide/ show code snippet with animation. It works well under iOS 14.5 private var additionalHeight: CGFloat { if UIDevice.current.hasNotch { return 0 } else { return self.navigationController?.view.safeAreaInsets.top ?? 0 } } private var statusBarHidden: Bool = false { didSet { if statusBarHidden { self.navigationController?.additionalSafeAreaInsets.top = additionalHeight } else { self.navigationController?.additionalSafeAreaInsets.top = 0 } UIView.animate(withDuration: Constants.config_shortAnimTime) { () -> Void in self.setNeedsStatusBarAppearanceUpdate() } } } // https://medium.com/@badlands/unfortunately-this-also-applies-to-ipad-pro-which-have-non-zero-safeareainsets-e1aa0d002462 extension UIDevice { /// Returns 'true' if the current device has a notch var hasNotch: Bool { if #available(iOS 11.0, *) { // https://stackoverflow.com/a/57899013/72437 let keyWindow = UIWindow.key // Case 1: Portrait && top safe area inset >= 44 let case1 = !UIDevice.current.orientation.isLandscape && (keyWindow?.safeAreaInsets.top ?? 0) >= 44 // Case 2: Lanscape && left/right safe area inset > 0 let case2 = UIDevice.current.orientation.isLandscape && ((keyWindow?.safeAreaInsets.left ?? 0) > 0 || (keyWindow?.safeAreaInsets.right ?? 0) > 0) return case1 || case2 } else { // Fallback on earlier versions return false } } } iOS 14.5 However, when same code runs in iOS 15, the animation is broken. We use latest XCode 13.0 During hide, there is no more "slide up" hide animation. During show, it will try to "push down" the entire view controller. iOS 15 Does anyone has idea how to fix such animation in iOS 15, so that it behaves similar as iOS 14.5 ?

I want to start learning to use NSAsynchronousFetchRequest by referring to  https://www.marcosantadev.com/coredata_crud_concurrency_swift_2/ I have the simplest use case of NSAsynchronousFetchRequest NSAsynchronousFetchRequest // Call from UI main thread func X() { let fetchRequest = NSFetchRequest<NSPlainNote>(entityName: "NSPlainNote") let asynchronousFetchRequest = NSAsynchronousFetchRequest(fetchRequest: fetchRequest) { asynchronousFetchResult in guard let result = asynchronousFetchResult.finalResult as? [NSPlainNote] else { return } } let coreDataStack = CoreDataStack.INSTANCE // backgroundContext created via persistentContainer.newBackgroundContext() let backgroundContext = coreDataStack.backgroundContext backgroundContext.perform { do { try backgroundContext.execute(asynchronousFetchRequest) } catch let error { backgroundContext.rollback() error_log(error) } } } However, running the above code will get me the following error CoreData`+[NSManagedObjectContextMultithreading_Violation_AllThatIsLeftToUsIsHonor]: If I modify the code by using NSFetchRequest directly. NSFetchRequest // Call from UI main thread func X() { let fetchRequest = NSFetchRequest<NSPlainNote>(entityName: "NSPlainNote") let coreDataStack = CoreDataStack.INSTANCE // backgroundContext created via persistentContainer.newBackgroundContext() let backgroundContext = coreDataStack.backgroundContext backgroundContext.perform { do { let nsPlainNotes = try fetchRequest.execute() } catch let error { backgroundContext.rollback() error_log(error) } } } Thing works fine. May I know, what's wrong with my NSAsynchronousFetchRequest version of code? This is my CoreDataStack.swift for reference purpose. CoreDataStack.swift import CoreData class CoreDataStack { static let INSTANCE = CoreDataStack() private init() { } private(set) lazy var persistentContainer: NSPersistentContainer = { let container = NSPersistentContainer(name: "wenote") container.loadPersistentStores(completionHandler: { (storeDescription, error) in if let error = error as NSError? { // This is a serious fatal error. We will just simply terminate the app, rather than using error_log. fatalError("Unresolved error \(error), \(error.userInfo)") } }) // So that when backgroundContext write to persistent store, container.viewContext will retrieve update from // persistent store. container.viewContext.automaticallyMergesChangesFromParent = true // TODO: Not sure these are required... // //container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy //container.viewContext.undoManager = nil //container.viewContext.shouldDeleteInaccessibleFaults = true return container }() private(set) lazy var backgroundContext: NSManagedObjectContext = { let backgroundContext = persistentContainer.newBackgroundContext() // Similar behavior as Android's Room OnConflictStrategy.REPLACE backgroundContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy // TODO: Not sure these are required... //backgroundContext.undoManager = nil return backgroundContext }() } Additional information Do note that, in NSAsynchronousFetchRequest example, even if backgroundContext.perform is not used. // Call from UI main thread func X() { let fetchRequest = NSFetchRequest<NSPlainNote>(entityName: "NSPlainNote") let asynchronousFetchRequest = NSAsynchronousFetchRequest(fetchRequest: fetchRequest) { asynchronousFetchResult in guard let result = asynchronousFetchResult.finalResult as? [NSPlainNote] else { return } } let coreDataStack = CoreDataStack.INSTANCE // backgroundContext created via persistentContainer.newBackgroundContext() let backgroundContext = coreDataStack.backgroundContext do { try backgroundContext.execute(asynchronousFetchRequest) } catch let error { backgroundContext.rollback() error_log(error) } } Same fatal error still occur. Please note that, this fatal error will only be triggered, by editing the schema with Arguments Passed On Launch -com.apple.CoreData.ConcurrencyDebug 1 I even try to execute some simple project from  https://github.com/abhishekbedi1432/Core-Data-Asynchronous-Fetching/tree/master which is using NSAsynchronousFetchRequest. If I do not enable -com.apple.CoreData.ConcurrencyDebug 1, the sample project from github able to perform asynchronous fetch without issue. However, once the -com.apple.CoreData.ConcurrencyDebug 1 is enabled, it will also be getting the same fatal error.

It seems there are 2 ways to perform asynchronous read in CoreData, without blocking main thread UI. newBackgroundContext + FetchRequest Source : https://www.advancedswift.com/core-data-background-fetch-save-create/ // Create a new background managed object context let context = persistentContainer.newBackgroundContext() // If needed, ensure the background context stays // up to date with changes from the parent context.automaticallyMergesChangesFromParent = true // Perform operations on the background context // asynchronously context.perform { do { // Create a fetch request let fetchRequest: NSFetchRequest<CustomEntity> fetchRequest = CustomEntity.fetchRequest() fetchRequest.fetchLimit = 1 let objects = try context.fetch(fetchRequest) // Handle fetched objects } catch let error { // Handle error } } newBackgroundContext + NSAsynchronousFetchRequest Source: https://www.marcosantadev.com/coredata_crud_concurrency_swift_2/ let privateManagedObjectContext = persistentContainer.newBackgroundContext() // Creates a fetch request to get all the dogs saved let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Dog") // Creates `asynchronousFetchRequest` with the fetch request and the completion closure let asynchronousFetchRequest = NSAsynchronousFetchRequest(fetchRequest: fetchRequest) { asynchronousFetchResult in // Retrieves an array of dogs from the fetch result `finalResult` guard let result = asynchronousFetchResult.finalResult as? [Dog] else { return } // Dispatches to use the data in the main queue DispatchQueue.main.async { // Do something } } do { // Executes `asynchronousFetchRequest` try privateManagedObjectContext.execute(asynchronousFetchRequest) } catch let error { print("NSAsynchronousFetchRequest error: \(error)") } However, note that, the above code will unfortunately cause fatal error, if I were to enable flag -com.apple.CoreData.ConcurrencyDebug 1. So far, I do not have a good solution to such. For more detail, please refer to https://developer.apple.com/forums/thread/697718 ? May I know, what is the difference among newBackgroundContext + FetchRequest vs newBackgroundContext + NSAsynchronousFetchRequest? How should I choose one over another? Thank you.

Is using CoreData + CloudKit to store text notes and iCloud Document to store note image attachments as image files a good design approach? Currently, I have almost finished implementing the app to store text notes as Core Data and note image attachments as image files. I like to provide iCloud storage support to the app. I come across a few app examples https://www.raywenderlich.com/13219461-getting-started-with-core-data-and-cloudkit https://developer.apple.com/documentation/coredata/synchronizing_a_local_store_to_the_cloud Both examples are using CoreData + CloudKit to store the image as SQLite blob binary data which CoreData will perform such task automatically) I'm aware that when storing the binary image into CoreData, CoreData is smart enough to choose either to store it as a binary blob in SQLite, or an external file. However, I am a little skeptical about such an approach We are using Kingfisher for smooth image loading in the collection view. If the image data are not in a regular flat-file, how can we integrate CoreData's blob data with Kingfisher? Storing images in CoreData seems like a black box. If something goes wrong in between, it is hard to debug where and how goes wrong. We like to provide alternative cloud storage (using cloud S3 storage to store SQLite files and multiple images) for the app. So, saving the image as flat files will make such an effort easier. Some related discussion on storing the image in DB vs flat files - https://stackoverflow.com/questions/3748/storing-images-in-db-yea-or-nay I would prefer Only use CoreData + CloudKit to store the text note and file path. The image file will store in both the app folder and the iCloud document folder (so that it syncs seamlessly to iCloud). If the required images are not in the app folder (App uninstall, then re-install), the app will try to copy the image file from the iCloud document I was wondering, anyone of you has tried such a design in your app? Do you find it is a good approach based on your experience? Thanks.

I still fail to understand, what is the problem NSPersistentHistoryTransaction is trying to solve, in the CoreDataCloudKitDemo WWDC 2019 "Using Core Data with CloudKit" https://github.com/software123inc/CoreDataCloudKitDemo/blob/master/CoreDataCloudKitDemo/DataProvider/CoreDataStack.swift#L161 I want to see, what problem will occur, if processPersistentHistory is not executed. By making the processPersistentHistory empty, I try to do the following testing. Run 2 simulators simultaneously in the same machine. Add an item to simulator A. Since, there is no way for simulator B to receive push notification, I press the home button for simulator B. In simulator B, I tap on the app icon to launch the app again. In simulator B, I can observe controllerDidChangeContent is being called. My guess is that, because the backed SQLite is seamlessly updated by CloudKit background task, NSFetchedResultController will be notified the SQLite DB change, and subsequently update the UI. Check the "Download CloudKit Changes into Core Data" of https://developer.apple.com/documentation/coredata/mirroring_a_core_data_store_with_cloudkit/syncing_a_core_data_store_with_cloudkit In simulator B, due to controllerDidChangeContent is being triggered correctly, I can observe the UI change perform by NSFetchResultController without issue. Hence, I am not clear, on what problem processPersistentHistory is trying to solve in the demo code. May I know what kind of test case I can perform, to understand the problem solved by processPersistentHistory? Based on "Integrate Store Changes Relevant to the Current View" https://developer.apple.com/documentation/coredata/mirroring_a_core_data_store_with_cloudkit/syncing_a_core_data_store_with_cloudkit Your app receives remote change notifications when the local store updates from CloudKit. However, it’s unnecessary to update your UI in response to every notification, because some changes may not be relevant to the current view. Analyze the persistent history to determine whether the changes are relevant to the current view before consuming them in the user interface. Inspect the details of each transaction, such as the entity name, its updated properties, and the type of change, to decide whether to act. For more information about persistent history tracking, see Consuming Relevant Store Changes. This part is getting confusing. Our NSFetchedResultController is receiving relevant entity change event due to SQLite, and subsequently able to update the UI correct. If that is so, why do we still need persistent history?

We wish to implement in-app purchase for our app, which is currently targeting 14.3 The latest StoreKit 2, is only available for iOS 15 We wish to study how should we implement such, by looking at official code example of StoreKit 1. However, the current posted code at Apple site, is only available for StoreKit 2 - https://developer.apple.com/documentation/storekit/in-app_purchase/implementing_a_store_in_your_app_using_the_storekit_api Does anyone have any idea, where can I get the official StoreKit 1 code example, from Apple? Thanks.

In iOS15, we have an efficient way to update items cell, by using reconfigureItems. Here's the code snippet to perform such efficient update. Update items cell efficiently using reconfigureItems private func reconfigureRecordingRow(_ recording: Recording) { var snapshot = dataSource.snapshot() snapshot.reconfigureItems([recording]) dataSource.apply(snapshot) } private func makeDataSource() -> DataSource { let dataSource = DataSource( collectionView: collectionView, cellProvider: { [weak self] (collectionView, indexPath, anyHashable) -> UICollectionViewCell? in guard let self = self else { return nil } guard let recordingCell = collectionView.dequeueReusableCell( withReuseIdentifier: "recording", for: indexPath) as? RecordingCell else { return nil } When reconfigureRecordingRow is called, cellProvider's function will be executed. collectionView.dequeueReusableCell is able to re-use existing UICollectionViewCell, without constructing new UICollectionViewCell However, I was wondering, how can I achieve a similar efficiency, if I have a section, with header supplementary view, and without any item? For instance Not able to update supplementary view efficiently private func reloadAttachmentRow() { var snapshot = dataSource.snapshot() let sectionIdentifiers = snapshot.sectionIdentifiers if sectionIdentifiers.contains(.attachment) { snapshot.reloadSections([.attachment]) } else { snapshot.insertSections([.attachment], beforeSection: .title) } dataSource.apply(snapshot) } dataSource.supplementaryViewProvider = { [weak self] collectionView, kind, indexPath in guard let self = self else { return nil } if kind == UICollectionView.elementKindSectionHeader { let section = indexPath.section let sectionIdentifier = self.sectionIdentifier(section) switch sectionIdentifier { case .attachment: guard let collageViewHeader = collectionView.dequeueReusableSupplementaryView( ofKind: kind, withReuseIdentifier: "attachment", for: indexPath) as? CollageViewHeader else { return nil } When reloadSections is called, dataSource.supplementaryViewProvider will be executed. As per my testing, collectionView.dequeueReusableSupplementaryView will return a new instance of UICollectionReusableView each time. As a result, I can visually observe the entire section is "flickering", when reloadAttachmentRow is called. I was wondering, how can we update supplementary view efficiently?

I'm using NSMetadataQuery and NotificationCenter, to perform file downloading from iCloud. Construct NSMetadataQuery with predicate NSPredicate(format: "%K == %@", NSMetadataItemFSNameKey, filename) Observe NSMetadataQueryDidUpdate & NSMetadataQueryDidFinishGathering using NotificationCenter. Check file status NSMetadataUbiquitousItemDownloadingStatusKey. If the file is up-to-date, copy the file to destination directory, and jump to step 6. Perform FileManager.default.startDownloadingUbiquitousItem Receive file downloading status in NSMetadataQueryDidUpdate callback. If the file is up-to-date, copy the file to destination directory, and jump to step 6. Perform cleanup by removing all observers. If file is not available in iCloud, no notification received. We wish, even if the file doesn't exist, we will still be notified, so that we have chance to perform cleanup (step 6) Here's the code snippet to perform iCloud download. DownloadManager.swift class DownloadManager { static let INSTANCE = DownloadManager() var downloaders = [iCloudDocumentDownloader]() private init() { } func append(filename: String, destinationDirectory: URL) { let downloader = iCloudDocumentDownloader(filename: filename, destinationDirectory: destinationDirectory) downloaders.append(downloader) } func removeAll(_ downloader: iCloudDocumentDownloader) { downloaders.removeAll{$0 === downloader} } } iCloudDocumentDownloader.swift class iCloudDocumentDownloader { private let filename: String private let destinationDirectory: URL private let metadataQuery = NSMetadataQuery() private static let operationQueue: OperationQueue = { let operationQueue = OperationQueue() operationQueue.name = "com.yocto.wenote.operationQueueForiCloudDocument" operationQueue.maxConcurrentOperationCount = 1 operationQueue.qualityOfService = .userInitiated return operationQueue }() deinit { NotificationCenter.default.removeObserver(self) } private func bye() { DownloadManager.INSTANCE.removeAll(self) } init(filename: String, destinationDirectory: URL) { self.filename = filename self.destinationDirectory = destinationDirectory metadataQuery.operationQueue = iCloudDocumentDownloader.operationQueue metadataQuery.predicate = NSPredicate(format: "%K == %@", NSMetadataItemFSNameKey, filename) metadataQuery.searchScopes = [ NSMetadataQueryUbiquitousDocumentsScope ] NotificationCenter.default.addObserver(self, selector: #selector(didUpdate), name: NSNotification.Name.NSMetadataQueryDidUpdate, object: metadataQuery) NotificationCenter.default.addObserver(self, selector: #selector(didFinishGathering), name: NSNotification.Name.NSMetadataQueryDidFinishGathering, object: metadataQuery) metadataQuery.start() } @objc func didUpdate(_ notification: Notification) { guard let metadataQuery = notification.object as? NSMetadataQuery else { return } metadataQuery.enumerateResults { [weak self] (item: Any, index: Int, stop: UnsafeMutablePointer<ObjCBool>) in guard let self = self else { return } guard let metadataItem = item as? NSMetadataItem else { return } guard let status = metadataItem.value(forAttribute: NSMetadataUbiquitousItemDownloadingStatusKey) as? String else { return } guard let url = metadataItem.value(forAttribute: NSMetadataItemURLKey) as? URL else { return } if status == NSMetadataUbiquitousItemDownloadingStatusCurrent { if !destinationDirectory.createCompleteDirectoryHierarchyIfDoesNotExist() { self.bye() // Early return. return } let destinationURL = destinationDirectory.appendingPathComponent(filename, isDirectory: false) do { try FileManager.default.copyItem(at: url, to: destinationURL) } catch { error_log(error) } self.bye() } else if let error = metadataItem.value(forAttribute: NSMetadataUbiquitousItemDownloadingErrorKey) as? NSError { error_log(error) self.bye() } else { } } } @objc func didFinishGathering(_ notification: Notification) { guard let metadataQuery = notification.object as? NSMetadataQuery else { return } metadataQuery.enumerateResults { [weak self] (item: Any, index: Int, stop: UnsafeMutablePointer<ObjCBool>) in guard let self = self else { return } guard let metadataItem = item as? NSMetadataItem else { return } guard let status = metadataItem.value(forAttribute: NSMetadataUbiquitousItemDownloadingStatusKey) as? String else { return } guard let url = metadataItem.value(forAttribute: NSMetadataItemURLKey) as? URL else { return } if status == NSMetadataUbiquitousItemDownloadingStatusCurrent { if !destinationDirectory.createCompleteDirectoryHierarchyIfDoesNotExist() { self.bye() // Early return. return } let destinationURL = destinationDirectory.appendingPathComponent(filename, isDirectory: false) do { try FileManager.default.copyItem(at: url, to: destinationURL) } catch { error_log(error) } self.bye() } else if let error = metadataItem.value(forAttribute: NSMetadataUbiquitousItemDownloadingErrorKey) as? NSError { error_log(error) self.bye() } else { do { try FileManager.default.startDownloadingUbiquitousItem(at: url) } catch { error_log(error) self.bye() } } } } }

Due to privacy concern, we wish to provide a toggle switch, so that user has the freedom, to choose whether to sync CoreData with iCloud. We can implement such a feature by following suggestion from https://developer.apple.com/forums/thread/118924?login=true However, we should not perform history tracking transactions purging, once user disables CloudKit sync Reason is that, if few months later/ few years later, user decides to turn on CloudKit sync again, lack of sufficient history tracking transactions, will cause CloudKit sync fail. This is causing a dilemma. If we never clean the history tracking transactions, will it cause disk full issue? If that is so, may I know, what is the correct way to handle history tracking transactions purging, if we allow users to enable/ disable CloudKit sync? Thank you.

We notice PHPickerConfiguration will produce wrong ordering sometimes, during multi selection. Our app is targeting iOS 15, and the test is run on simulator iOS 15.5 Here the video to demonstrate the issue https://youtu.be/RrhqFuB2kqs Please note that, the standing cat picture suppose to be the 4th order. By looking at the console and UI outcome, it is mistakenly returned as 3rd order. Here's the code which show func chooseImage() { var configuration = PHPickerConfiguration() configuration.selectionLimit = 0 // https://developer.apple.com/documentation/photokit/phpickerconfiguration/selection configuration.selection = .ordered // GIF exclusion is still not supported - https://developer.apple.com/forums/thread/687415 configuration.filter = .images let picker = PHPickerViewController(configuration: configuration) picker.delegate = self present(picker, animated: true) } and here's the code which prints out the ordering of images. extension NewNoteViewController: PHPickerViewControllerDelegate { func picker(_ picker: PHPickerViewController, didFinishPicking results: [PHPickerResult]) { picker.dismiss(animated: true) guard !results.isEmpty else { return } var displayErrorOnce = false for result in results { result.itemProvider.loadFileRepresentation(forTypeIdentifier: UTType.image.identifier) { [weak self] (url, error) in precondition(!Thread.isMainThread) guard let self = self else { return } guard let url = url else { return } print(">>>> url \(url)") // ... } } } } This problem happens randomly. May I know, is there any workaround for this issue? Thank you.