From what I've read, @AppStorage vars should be @Published, however the following code generates a syntax error at extended's .sink modifier: Cannot call value of non-function type 'Binding<Subject>' class LanguageManager: ObservableObject { @Published var fred = "Fred" @AppStorage("extended") var extended: Bool = true private var subscriptions = Set<AnyCancellable>() init() { $fred .sink(receiveValue: {value in print("value: \(value)") }) .store(in: &subscriptions) $extended .sink(receiveValue: {value in print("value: \(value)") }) .store(in: &subscriptions) } Does anyone know of a way to listen for (subscribe to) changes in @AppStorage values? didSet works in for a specific subset of value changes, but this is not sufficient for my intended use.

I've defined a value stored in UserDefaults. In a view struct I have code that can successfully update the stored value. I've also added an @AppStorage var in an instance of a class, that can read this value and run business logic that depends on the current stored value. But what I really want to do, is have code in my class that gets automatically called when the value stored in UserDefaults gets updated. Basically I want to do this: @AppStorage("languageChoice") var languageChoice: LanguageChoice = .all { didSet { print("hello") } } Unfortunately didSet closures in @AppStorage vars do not appear to get called :-( My clumsy attempts to use combine have all ended in tears from the compiler. Any/all suggestions are greatly appreciated. thanks, Mike

Hi, Is there any way to return cached URLSession response and then reload and return? I want show cached response while load last version of API call, and if reload works fine, show the latest version of response and in case os failure, show cached response (if exists) Thanks!

I'm just putting this here for visibility, I already submitted FB13688825. If you say this: Task { for await tracks in avPlayerItem.publisher(for: \.tracks, options: [.initial]).values { print("*** fired with: \(tracks.description)") } } ...it fires once with: "*** fired with: []" If you say this: avPlayerItem.publisher(for: \.tracks).sink { [weak self] tracks in print("*** fired with: \(tracks.description)") }.store(in: &subscriptions) ...you get, as expected, multiple fires, most with data in them such as: *** fired with: [<AVPlayerItemTrack: 0x10a9869a0, assetTrack = <AVAssetTrack: 0x10a9869f0... I think it's a bug but I'm just going to go back to the "old way" for now. No emergency.

I am maintaining a macOS app, a GUI on top of a command line tool. A Process() object is used to kick off the command line tool with arguments. And completion handlers are triggered for post actions when command line tool is completed. My question is: I want to refactor the process to use async and await, and not use completion handlers. func execute(command: String, arguments:[String]) -&gt; async { let task = Process() task.launchPath = command task.arguments = arguments ... do { try task.run() } catch let e { let error = e propogateerror(error: error) } ... } ... and like this in calling the process await execute(..) Combine is used to monitor the ProcessTermination: NotificationCenter.default.publisher( for: Process.didTerminateNotification) .debounce(for: .milliseconds(500), scheduler: DispatchQueue.main) .sink { _ in ..... // Release Combine subscribers self.subscriptons.removeAll() }.store(in: &amp;subscriptons) Using Combine works fine by using completion handlers, but not by refactor to async. What is the best way to refactor the function? I know there is a task.waitUntilExit(), but is this 100% bulletproof? Will it always wait until external task is completed?

class MyModel: ObservableObject { @Published var selection = FamilyActivitySelection() init() { $selection.sink { newSelection in print(newSelection) } } } class MyView: View { @StateObject var model = MyModel() // some body // .... // my method func removeToken(token: ApplicationToken) { model.selection.applicationTokens.remove(token) } } I am using the above code. When I call removeToken, the callback from the sink (which is registered in init() of MyModel) is called without any changes. newSelection still contains the token that I removed. Currently, I am using the additional code below to work around the problem. .onChange(of: model.selection.applicationTokens) { newSet in model.selection.applicationTokens = newSet } Should I use the workaround solution, or am I missing something?

It feels like this should be easy, but I'm having conceptual problems about how to do this. Any help would be appreciated. I have a sample app below that works exactly as expected. I'm able to use the Slider and Stepper to generate inputs to a function that uses CoreImage filters to manipulate my input image. This all works as expected, but it's doing some O(n) CI work on the main thread, and I want to move it to a background thread. I'm pretty sure this can be done using combine, here is the pseudo code I imagine would work for me: func doStuff() { // subscribe to options changes // .receive on background thread // .debounce // .map { model.inputImage.combine(options: $0) // return an object on the main thread. // update an @Published property? } Below is the POC code for my project. Any guidance as to where I should use combine to do this would be greatly appreciate. (Also, please let me know if you think combine is not the best way to tackle this. I'd be open to alternative implementations.) struct ContentView: View { @State private var options = CombineOptions.basic @ObservedObject var model = Model() var body: some View { VStack { Image(uiImage: enhancedImage) .resizable() .aspectRatio(contentMode: .fit) Slider(value: $options.scale) Stepper(value: $options.numberOfImages, label: { Text("\(options.numberOfImages)")}) } } private var enhancedImage: UIImage { return model.inputImage.combine(options: options) } } class Model: ObservableObject { let inputImage: UIImage = UIImage.init(named: "IMG_4097")! } struct CombineOptions: Codable, Equatable { static let basic: CombineOptions = .init(scale: 0.3, numberOfImages: 10) var scale: Double var numberOfImages: Int }

Following this Apple Article, I copied their code over for observePlayingState(). The only difference I am using @Observable instead of ObservableObject and @Published for var isPlaying. We get a bit more insight after removing the $ symbol, leading to a more telling error of: Cannot convert value of type 'Bool' to expected argument type 'Published.Publisher' Is there anyway to get this working with @Observable?

Hi all, I have some code that works on iOS 14 up to 16 and now suddenly doesn't work on iOS 17 so I guess it's a regression. Here's a snippet of a minimal reproducible example. SubView is supposed to update correctly when the button is pressed but that's not happening on iOS 17. onChange is not called either. struct ContentView: View { @ObservedObject var viewModel: ViewModel var body: some View { SubViewContainer(wrapper: $viewModel.wrapper) } } struct SubViewContainer: View { @Binding var wrapper: ValueWrapper var body: some View { SubView(value: $wrapper.value) } } struct SubView: View { @Binding var value: Bool var body: some View { Button(action: { value.toggle() }) { Text(value ? "true" : "false") } } } class ViewModel: ObservableObject { @Published var wrapper = ValueWrapper() } class ValueWrapper: ObservableObject { @Published var value = true } Any clue what is going on?

I have a regular app and an app with LSUIElement=YES. Both have Swift app lifecycle main entry points. Both have an app group ".com.company.app". Both can read and write prefs and see each other's values. But I can't for the life of me get changes from one app to notify the other. At first I tried NotificationCenter, but then learned (thanks to this thread) that you have to use KVO or Combine. I tried both. Both get the initial value, but never see subsequent changes. Combine seems to just wrap KVO, looking at the stack trace. I'm subscribing to updates like this: let defaults = UserDefaults(suiteName: "<TEAMID>.com.company.app")! defaults .publisher(for: \.enabled) .handleEvents(receiveOutput: { enabled in print("Enabled is now: \(enabled)") }) .sink { _ in } .store(in: &subs) … extension UserDefaults { @objc var enabled: Bool { get { return bool(forKey: "Enabled") } set { set(newValue, forKey: "Enabled") } } } I'm writing to prefs like this: let defaults = UserDefaults(suiteName: "<TEAMID>.com.company.app")! defaults.set(enabled, forKey: "Enabled") Am I missing something?

Given that SwiftUI and modern programming idioms promote asynchronous activity, and observing a data model and reacting to changes, I wonder why it's so cumbersome in Swift at this point. Like many, I have run up against the problem where you perform an asynchronous task (like fetching data from the network) and store the result in a published variable in an observed object. This would appear to be an extremely common scenario at this point, and indeed it's exactly the one posed in question after question you find online about this resulting error: Publishing changes from background threads is not allowed Then why is it done? Why aren't the changes simply published on the main thread automatically? Because it isn't, people suggest a bunch of workarounds, like making the enclosing object a MainActor. This just creates a cascade of errors in my application; but also (and I may not be interpreting the documentation correctly) I don't want the owning object to do everything on the main thread. So the go-to workaround appears to be wrapping every potentially problematic setting of a variable in a call to DispatchQueue.main. Talk about tedious and error-prone. Not to mention unmaintainable, since I or some future maintainer may be calling a function a level or two or three above where a published variable is actually set. And what if you decide to publish a variable that wasn't before, and now you have to run around checking every potential change to it? Is this not a mess?

Using ImageCaptureCore, to send PTP devices to cameras via tether, I noticed that all of my Nikon cameras can take up to an entire minute for PTP events to start logging. My Canons and Sonys are ready instantly. Any idea why? I use the ICDeviceBrowser to browse for cameras, and then request to open the session. According to the docs, it says it's ready after it enumerates its objects? If that's the case, is there a way to bypass that? Even on an empty SD card it's slow.

That may not be the best way to explain it. Essentially, I'm requesting data from Reddit and storing it in an object called Request. This object has a timestamp and an array of objects called Post. Everything was working fine until I started to add some code to filter the post that were being fetched from reddit. extension [Request] { func insert(request: Request, in context: ModelContext) { if self.count == 0 { context.logMessage("There are no existing request") context.insert(request) context.logMessage("Request saved") }else { print(request) // No crash print(request.timestamp) // No crash print(request.posts) // Causes a crash } } } When it does crash, it points to this code inside the SwiftData model. This code seems to be something within SwiftData. I didn't write any of this. { @storageRestrictions(accesses: _$backingData, initializes: _posts) init(initialValue) { _$backingData.setValue(forKey: \.posts, to: initialValue) _posts = _SwiftDataNoType() } get { _$observationRegistrar.access(self, keyPath: \.posts) return self.getValue(forKey: \.posts) } set { _$observationRegistrar.withMutation(of: self, keyPath: \.posts) { self.setValue(forKey: \.posts, to: newValue) } } } It has the error at the return self.getValue() line: Thread 5: EXC_BREAKPOINT (code=1, subcode=0x2406965c4) This is the sequence that occurs: View is loaded Checks if it should load a new request If it should, it calls this function private func requestNewData() { redditService.fetchRedditAllData(completion: { result in DispatchQueue.main.async { switch result { case .success(let newRequest): modelContext.logMessage("Successfully retreived and decoded data from Reddit") // Log the success //modelContext.insert(newRequest) requests.insert(request: newRequest, in: modelContext) case .failure: modelContext.logMessage("Failed to retrieve and decode data from Reddit") } } }) } The code for the fetch function is here: func fetchRedditAllData(completion: @escaping (Result<Request, Error>) -> Void) { // Try to construct the URL and return if it fails guard let url = URL(string: RedditRequests.all) else { context.logMessage("Failed to contruct the url for r/all") return } // Try to retrieve data from the URL session.dataTask(with: url, completionHandler: { data, _, error in // If it fails, log the failure if let error = error { self.context.logMessage("Failed to retrieve data from the r/all URL.\n\(error.localizedDescription)") } else { // If it doesn't fail, try to decode the data do { let data = data ?? Data() // Get data let response = try self.decoder.decode(Request.self, from: data) // Decode JSON into Request model completion(.success(response)) // Return response (request) if successful self.context.logMessage("Decoded data") } catch { completion(.failure(error)) self.context.logMessage("Failed to decode data into a Request.\n\(error.localizedDescription)") } } }).resume() } If I don't try to access request.posts before saving it to the context, it works fine. It will fetch the data and store it to the phone and then display it on the phone. When I try to access request.posts to do some filtering, it crashes. Does anyone have any ideas?

I've made a small reproducing example app to demonstrate this issue. Just create an iOS App project and replace the App and ContentView files with the following code. The app works as expected when running it in a simulator or on a device but the SwiftUI Preview will get stuck showing only the loading state, even though the print statement in the View's body has printed viewModel.state: showingContent(SwiftUITest.ViewModel.Content(text: "Hello world!", reloadButtonTitle: "Reload"))to the console. When stuck showing the loading state (an animated ProgressView), If I change .padding(.all, 12) to e.g. .padding(.all, 2) or vice versa, then that will make the Preview render the expected content. Also, if I tap the Reload-button, it will not show the ProgressView for 2 seconds as expected (and as the app will do when run in a simulator or on a device), instead it will just show a white screen, and the same workaround (changing the padding amount) can be used to make the it render the expected content. Can other people reproduce this behavior, is it a known bug, or am I doing something wrong? TestApp.swift import SwiftUI @main struct SwiftUITestApp: App { var body: some Scene { WindowGroup { ContentView(viewModel: ViewModel( contentLoader: { try! await Task.sleep(nanoseconds: 2_000_000_000) return .init(text: "Hello world!", reloadButtonTitle: "Reload") } )) } } } ContentView.swift import SwiftUI struct ContentView: View { @StateObject var viewModel: ViewModel var body: some View { let _ = print("viewModel.state:", viewModel.state) Group { switch viewModel.state { case .notStarted, .loading: ProgressView() case .showingContent(let content): VStack { Text(content.text) .padding(.all, 12) Button(content.reloadButtonTitle) { viewModel.handle(event: .reloadButtonWasTapped) } } } } .onAppear { viewModel.handle(event: .viewDidAppear) } } } // MARK: - ViewModel @MainActor final class ViewModel: ObservableObject { @Published var state: State = .notStarted let contentLoader: () async -> Content init(contentLoader: @escaping () async -> Content) { self.contentLoader = contentLoader } func handle(event: Event) { switch state { case .notStarted: if event == .viewDidAppear { loadContent() } case .loading: break case .showingContent: if event == .reloadButtonWasTapped { loadContent() } } } func loadContent() { guard state != .loading else { return } state = .loading Task { print("starts loading", Date.now) let content = await contentLoader() print("finished loading", Date.now) state = .showingContent(content) } } enum State: Equatable { case notStarted case loading case showingContent(Content) } struct Content: Equatable { let text: String let reloadButtonTitle: String } enum Event: Equatable { case viewDidAppear case reloadButtonWasTapped } } // MARK: - Preview struct ContentView_Previews: PreviewProvider { static var previews: some View { ContentView(viewModel: ViewModel( contentLoader: { try! await Task.sleep(nanoseconds: 2_000_000_000) return .init(text: "Hello world!", reloadButtonTitle: "Reload") } )) } } Here's the simple behavior of the app (recorded from simulator): Each time the view appears, it loads it's content for two seconds while showing a ProgressView, then it shows the content, which includes a Reload button, and if you tap that button it will reload the content for 2 seconds again. I would expect the Preview to behave in the same way.

I'm learning Combine. I'm trying to understand some behavior when there is concurrent queue applied to receiveOn as a scheduler. I extracted code to present the situation that I'm trying to understand. let queue = DispatchQueue.global() // Or OperationQueue() let subscription = (1...10).publisher .receive(on: queue) .sink { value in print("Received \(value)") } I'm receiving in debug console such output: Received 1 Received 2 Received 3 Received 7 Received 6 But I was expecting 10 lines in the output. Everytime I run it I'm receiving different results but not 10 lines - 10 values. What is happening here? Does anybody know? Where is 4, 5, 8, 9 and 10? Why completion is arriving faster before all values? Is this a combine bug? I was looking in 2 books related to Combine and in apple documentation. No warnings about using concurrent queues as a schedulers in Combine.

We currently have our entire app written as SwiftUI Views with ViewModels (currently set as @StateObjects). SwiftUI has a new feature in iOS 17 called @Observable which simplifies the MVVM pattern and would greatly reduce the complexity of our codebase. However, our current ViewModels implement Combine pipelines on the @Published properties which allows us to do all sorts of things from validation of inputs to ensuring lists are filtered correctly. Without the @Published property wrapper in the new @Observable macro, we don't have access to those combine pipelines and so we were wondering how others have solved this? One idea we are floating around is using CurrentValueSubjects as the variable types, but that does pollute the code a little as we have to utilise .send() and .value in the Views which seems like an anti-pattern. Any thoughts or help would be greatly appreciated!

Hi, I'm trying to use async/await for KVO and it seems something is broken. For some reason, it doesn't go inside for in body when I'm changing the observed property. import Foundation import PlaygroundSupport class TestObj: NSObject {   @objc dynamic var count = 0 } let obj = TestObj() Task {   for await value in obj.publisher(for: \.count).values {     print(value)   } } Task.detached {   try? await Task.sleep(for: .microseconds(100))   obj.count += 1 } Task.detached {   try? await Task.sleep(for: .microseconds(200))   obj.count += 1 } PlaygroundPage.current.needsIndefiniteExecution = true Expected result: 0, 1, 2 Actual result: 0 Does anyone know what is wrong here?

I am working on a library, a Swift package. We have quite a few properties on various classes that can change and we think the @Published property wrapper is a good way to annotate these properties as it offers a built-in way to work with SwiftUI and also Combine. Many of our properties can change on background threads and we've noticed that we get a purple runtime issue when setting the value from a background thread. This is a bit problematic for us because the state did change on a background thread and we need to update it at that time. If we dispatch it to the main queue and update it on the next iteration, then our property state doesn't match what the user expects. Say they "load" or "start" something asynchronously, and that finishes, the status should report "loaded" or "started", but that's not the case if we dispatch it to the main queue because that property doesn't update until the next iteration of the run loop. There also isn't any information in the documentation for @Published that suggests that you must update it on the main thread. I understand why SwiftUI wants it on the main thread, but this property wrapper is in the Combine framework. Also it seems like SwiftUI internally could ask to receive the published updates on the main queue and @Published shouldn't enforce a specific thread. One thing we are thinking about doing is writing our own property wrapper, but that doesn't seem to be ideal for SwiftUI integration and it's one more property wrapper that users of our package would need to be educated about. Any thoughts on direction? Is there anyway to break @Published from the main thread?

This code crashes ("Unexpectedly found nil while unwrapping an Optional value") import Combine class Receiver { &#9;&#9;var value: Int! &#9;&#9;var cancellables = Set<AnyCancellable>([]) &#9;&#9;init(_ p: AnyPublisher<Int,Never>) { &#9;&#9;&#9;&#9;p.assign(to: \.value, on: self).store(in: &cancellables) &#9;&#9;} } let receiver = Receiver(Just(5).eraseToAnyPublisher()) It does not crash if I use p.sink { self.value = $0 }.store(in: &cancellables) instead of the assign, and it does not crash if I do not use an optional for the value-property. To me this looks like a bug in Swift's constructor code, but maybe I am overlooking something?