Apple's sample code "AVReaderWriter: Offline Audio / Video Processing" has the following listing let writingGroup = dispatch_group_create() // Transfer data from input file to output file. self.transferVideoTracks(videoReaderOutputsAndWriterInputs, group: writingGroup) self.transferPassthroughTracks(passthroughReaderOutputsAndWriterInputs, group: writingGroup) // Handle completion. let queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) dispatch_group_notify(writingGroup, queue) { // `readingAndWritingDidFinish()` is guaranteed to call `finish()` exactly once. self.readingAndWritingDidFinish(assetReader, assetWriter: assetWriter) } in CynanifyOperation.swift (an NSOperation subclass that stylizes imported video and exports it). How would I get about writing this part in modern Swift so that it compiles and works? I've tried writing this as let writingGroup = DispatchGroup() // Transfer data from input file to output file. self.transferVideoTracks(videoReaderOutputsAndWriterInputs: videoReaderOutputsAndWriterInputs, group: writingGroup) self.transferPassthroughTracks(passthroughReaderOutputsAndWriterInputs: passthroughReaderOutputsAndWriterInputs, group: writingGroup) // Handle completion. writingGroup.notify(queue: .global()) { // `readingAndWritingDidFinish()` is guaranteed to call `finish()` exactly once. self.readingAndWritingDidFinish(assetReader: assetReader, assetWriter: assetWriter) } However, it's taking an extremely long time for self.readingAndWritingDidFinish(assetReader: assetReader, assetWriter: assetWriter) to be called, and my UI is stuck in the ProgressViewController with a loading spinner. Is there something I wrote incorrectly or missed conceptually in the Swift 5 version?

Apple's sample code Identifying Trajectories in Video contains the following delegate callback: func cameraViewController(_ controller: CameraViewController, didReceiveBuffer buffer: CMSampleBuffer, orientation: CGImagePropertyOrientation) { let visionHandler = VNImageRequestHandler(cmSampleBuffer: buffer, orientation: orientation, options: [:]) if gameManager.stateMachine.currentState is GameManager.TrackThrowsState { DispatchQueue.main.async { // Get the frame of rendered view let normalizedFrame = CGRect(x: 0, y: 0, width: 1, height: 1) self.jointSegmentView.frame = controller.viewRectForVisionRect(normalizedFrame) self.trajectoryView.frame = controller.viewRectForVisionRect(normalizedFrame) } // Perform the trajectory request in a separate dispatch queue. trajectoryQueue.async { do { try visionHandler.perform([self.detectTrajectoryRequest]) if let results = self.detectTrajectoryRequest.results { DispatchQueue.main.async { self.processTrajectoryObservations(controller, results) } } } catch { AppError.display(error, inViewController: self) } } } } However, instead of drawing UI whenever detectTrajectoryRequest.results exist (https://developer.apple.com/documentation/vision/vndetecttrajectoriesrequest/3675672-results), I'm interested in using the CMTimeRange provided by each result to construct a new video. In effect, this would filter down the original video to only frames with trajectories. How might I accomplish this, perhaps through writing only specific time ranges' frames from one AVFoundation video to a new AVFoundation video?

I'd like a user's upload operation that's started in the foreground to continue when they leave the app. Apple's article Extending Your App's Background Execution Time has the following code listing func sendDataToServer( data : NSData ) { // Perform the task on a background queue. DispatchQueue.global().async { // Request the task assertion and save the ID. self.backgroundTaskID = UIApplication.shared. beginBackgroundTask (withName: "Finish Network Tasks") { // End the task if time expires. UIApplication.shared.endBackgroundTask(self.backgroundTaskID!) self.backgroundTaskID = UIBackgroundTaskInvalid } // Send the data synchronously. self.sendAppDataToServer( data: data) // End the task assertion. UIApplication.shared.endBackgroundTask(self.backgroundTaskID!) self.backgroundTaskID = UIBackgroundTaskInvalid } } The call to self.sendAppDataToServer( data: data) is unclear. Is this where the upload operation would go, wrapped in Dispatch.global().sync { }?

The Swift book says that "to prevent strong reference cycles, delegates are declared as weak references." protocol SomeDelegate: AnyObject { } class viewController: UIViewController, SomeDelegate { weak var delegate: SomeDelegate? override func viewDidLoad() { delegate = self } } Say the class parameterizes a struct with that delegate class viewController: UIViewController, SomeDelegate { weak var delegate: SomeDelegate? override func viewDidLoad() { delegate = self let exampleView = ExampleView(delegate: delegate) let hostingController = UIHostingController(rootView: exampleView) self.present(hostingController, animated: true) } } struct ExampleView: View { var delegate: SomeDelegate! var body: some View { Text("") } } Should the delegate property in the struct also be marked with weak?

I observe when an AVPlayer finishes play in order to present a UIAlert at the end time. NotificationCenter.default.addObserver( self, selector: #selector(presentAlert), name: .AVPlayerItemDidPlayToEndTime, object: nil ) I've had multiple user reports of the alert happening where they're not intended, such as the middle of the video after replaying, and on other views. I'm unable to reproduce this myself, but my guess is that it's a threading issue since AVPlayerItemDidPlayToEndTime says "the system may post this notification on a thread other than the one used to registered the observer." How then do I make sure the alert is present on the main thread? Should I dispatch to the main queue from within my presentAlert function, or add the above observer with addObserver(forName:object:queue:using:) instead, passing in the main operation queue?

I have an app that currently depends on fetching the model through CloudKit, and is composed of value types. I'm considering adding Core Data support so that record modifications are robust regardless of network conditions. Core Data resources seem to always assume a model layer with reference semantics, so I'm not sure where to begin. Should I keep my top-level model type a struct? Can I? If I move my model to reference semantics, how might I bridge from past model instances that are fetched through CloudKit and then decoded? Thank you in advance.

How do you create a picker where the user's selection corresponds to different values of an enumerated type?