Question 69174 in IOS Swift Question posted in
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How to receive @Published var in main thread – Ios swift

I keep the Model as a Published var in the ViewModel and Observe it from the View.

When the model process goes into a background thread, if you publish the model value, the Xcode thread checker will react.

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.

Is issued.

@StateObject var viewModel = ViewModel()

class ViewModel: ObservableObject {

    @Published var model = Model()
    var thisValue:String {
        return model.thisValue // I want to use this value in view
    }

struct Model {
    var thisValue:String = "value" // I want to change this value on background threads.

I’d like to know how to receive the model value in the main thread, but
I didn’t quite understand and asked a question.

I would be very happy if you could tell me.

Tags:

2

Answers


  1. 0

    Don’t quite get what you are trying to do. But if you are not happy with DispatchQueue.main.async you may try one of the following options:

    Combine

    struct Model {
    var thisValue: String = "value"
}

class ViewModel: ObservableObject {
    @Published var model = Model()
    var thisValue: String {
        model.thisValue
    }
    func setThisValueInBackground() {
        DispatchQueue.global(qos: .background).async {
            Just(Model(thisValue: "newValue")).receive(on: RunLoop.main).assign(to: &self.$model)
        }
    }
}

    Unpublish your model and use property observer on it instead

    class ViewModelV2: ObservableObject {
    var model = Model() {
        didSet {
            thisValue = model.thisValue
        }
    }
    @Published private(set) var thisValue: String = ""
    func setThisValueInBackground() {
        DispatchQueue.global(qos: .background).async {
            self.model = Model(thisValue: "newValue")
        }
    }
}
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  2. 0

    Like Matt mentioned above, you want to "subscribe" to the model value using .receive(on:) and .sink

    Though I’m not sure how @StateObject comes into play, or if you need it. The basic format I’ve seen used is:

    class ViewModel {
    // this could be a computed property or...
    @Published var thisValue: SomeType
    // ...more viewModel logic that potentially changes the value of `thisValue`
}

class View: UIView {
    var viewModel: ViewModel
    var cancellables = Set<AnyCancellable>()

    // in viewDidLoad start your subscription to the viewModel's published property
    override func viewDidLoad() {
        super.viewDidLoad()
        viewModel.$thisValue
            .receive(on: DispatchQueue.main)
            .sink { [weak self] result in
                // do something with the result
            }
            .store(in: $cancellables)
    }
}

    Also, if the result is something really simple like a String and all you want to do is set a labels text property, instead of using .sink you can use .assign

    viewModel.$thisValue
    .receive(on: DispatchQueue.main)
    .assign(to: .text, on: label)
    .store(in: $cancellables)
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