Publishing changes from async model

Question

I'm attempting to figure out how to display a message to my users when some asynchronous code takes some time to run. So far I've used a sample I found online to create a popup banner and tied the message together using an ObservedObject of the async method on my view and Publishing the values.

My sample code project is on a public GitHub repository here. https://github.com/SimplyKyra/CodeAttempts

Right now I have an issue as when I set the variables in the async method I'm getting the following error: Publishing changes from background threads is not allowed; make sure to publish values from the main thread (via operators like receive(on:)) on model updates. Solutions online seem to fix this issue by updating the value on the @mainActor thread but I want these methods to run asynchronously AND update the user on what's happening. What's the best way to update my variables from this location?

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SimplyKyra

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Answer 1

In case anyone is looking into this in the future. I asked on StackOverflow (https://stackoverflow.com/questions/74159031/swiftui-publishing-changes-from-async-model) and was told to put it on the main thread with ‘@MainActor’ or use DispatchQueue.main.async. I enclosed each of my assignments with the DispatchQueue.main.async and it now works without the warnings.

For example my async method now looks like:

class myAsyncViewModel:  ObservableObject  {
    @Published var imageName: String = "questionmark"
    @Published var title: String = "title"
    @Published var subTitle: String = "subtitle"

    func thisMethodTakesTime() async -> String? {
        print("In method: \(imageName), \(title), \(subTitle)")
        DispatchQueue.main.async {
            self.title = "MY METHOD"
            self.subTitle = "Starting out!"
        }
        try? await Task.sleep(nanoseconds: 1_000_000_000)
        DispatchQueue.main.async {
            self.subTitle = "Between"
        }
        try? await Task.sleep(nanoseconds: 1_000_000_000)
        DispatchQueue.main.async {
            self.subTitle = "About to return. Success!"
        }
        print("In method: \(imageName), \(title), \(subTitle)")
        return "RETURN RESULT"
    }
}

Posted by

SimplyKyra

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Answer 2

In case anyone is looking into this in the future. I asked on StackOverflow (https://stackoverflow.com/questions/74159031/swiftui-publishing-changes-from-async-model) and was told to put it on the main thread with ‘@MainActor’ or use DispatchQueue.main.async. I enclosed each of my assignments with the DispatchQueue.main.async and it now works without the warnings.

For example my async method now looks like:

class myAsyncViewModel:  ObservableObject  {
    @Published var imageName: String = "questionmark"
    @Published var title: String = "title"
    @Published var subTitle: String = "subtitle"

    func thisMethodTakesTime() async -> String? {
        print("In method: \(imageName), \(title), \(subTitle)")
        DispatchQueue.main.async {
            self.title = "MY METHOD"
            self.subTitle = "Starting out!"
        }
        try? await Task.sleep(nanoseconds: 1_000_000_000)
        DispatchQueue.main.async {
            self.subTitle = "Between"
        }
        try? await Task.sleep(nanoseconds: 1_000_000_000)
        DispatchQueue.main.async {
            self.subTitle = "About to return. Success!"
        }
        print("In method: \(imageName), \(title), \(subTitle)")
        return "RETURN RESULT"
    }
}

Posted by

SimplyKyra

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Answer 3

Indeed was looking. Thanks for the tip!

Posted by

jtjaatin

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Publishing changes from async model

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