How can I catch that @Published has changed with combine ? (UIKit)

Question

It takes data in my @Published variable in CarDetailViewModel, but I could not pass the data inside this variable to the variable in the ViewController.

ViewModel:

class CarDetailViewModel: ObservableObject {
    @Published var carDetail: Car = Car(brand: "", features: CarFeatures(model: "", km: 0, year: 0, price: 0, image: "", gearType: "", fuelType: "", carVersion: ""))
    
    private var anyCancellable = Set<AnyCancellable>()
    var carSubject = PassthroughSubject<Car, Never>()
    
    func prepareCarDetail() {
        carSubject
            .sink {[weak self] car in
                self?.carDetail = car
                print("car: \(self?.carDetail)") // it is working.
            }
            .store(in: &anyCancellable)
    }
}

ViewController:

When the assignmentDataToUI function runs, the label on the screen is blank.

class CarDetailViewController: UIViewController {
    
    @IBOutlet weak var imageView: UIImageView!
    @IBOutlet weak var brandLabel: UILabel!
    @IBOutlet weak var modelLabel: UILabel!
    @IBOutlet weak var gearTypeLabel: UILabel!
    @IBOutlet weak var fuelTypeLabel: UILabel!
    @IBOutlet weak var priceLabel: UILabel!
    
    var carDetailViewModel = CarDetailViewModel()
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        
        carDetailViewModel.prepareCarDetail()
        assignmentDataToUI()
        
    }
    
    func assignmentDataToUI() {
        brandLabel.text = carDetailViewModel.carDetail.brand
    }
}

Unclear what the question is. You are subscribed to carSubject, not carDetail. — matt, Aug 18 '21 at 19:03
When @Published variable inside CarDetailViewModel changes, I want to pass this change to CarDetailViewController. — Ufuk Köşker, Aug 18 '21 at 19:08
The code above is not working. I have shared the working code below. @matt — Ufuk Köşker, Aug 18 '21 at 19:17
Well you're still not doing what you said you wanted to do. If you're going to fetch carDetail manually what's the point of making it Published? The point of Published is to subscribe and you are not doing so. — matt, Aug 18 '21 at 19:20
Just as I said in my first comment and all the comments since then. You would _subscribe_ to the Published `carDetail`. If you're not going to subscribe to it, there's no clear reason to make it a `@Published` property. It also isn't clear (to me at least) why CarDetailViewModel is an ObservableObject. — matt, Aug 18 '21 at 20:25
There you go, that's better. But of course this is trivially obvious so it's still hard to see what the question is for. — matt, Aug 18 '21 at 20:46
If the question I asked is wrong, I will delete this question. — Ufuk Köşker, Aug 18 '21 at 20:49

score 1 · Answer 1 · answered Aug 18 '21 at 20:37

I listened to carDetail in ViewModel with sink.

 carDetailViewModel.$carDetail
                .sink {[weak self] car in
                    guard let self = self else { return }
                    self.assignmentDataToUI()
                }
                .store(in: &anyCancelable)

score 0 · Answer 2 · answered Apr 08 '23 at 12:39

0

In ViewModel

 @Published var text: String = "befor"

In ViewController

private var cancellables = Set<AnyCancellable>()

......

viewModel.$text.sink { text in
   print(text)
}.store(in: &cancellables)

answered Apr 08 '23 at 12:39

Deep

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How can I catch that @Published has changed with combine ? (UIKit)

2 Answers2