How to solve "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." error?

URLSession.shared.dataTaskPublisher(for: urlRequest)

.tryMap {
   // your httpHandlerData
}
.receive(on: RunLoop.main)
.eraseToAnyPublisher()

Just add .receive(on: RunLoop.main) operator before .eraseToAnyPublisher() and That's it.

Code Block     @UserDefault("keyTwitterOauthTokenSecret", defaultValue: "")
    var twitterOauthTokenSecret: String {
        willSet{
            objectWillChange.send(self)
        }
    }
    init() {
        notificationSubscription = NotificationCenter.default.publisher(for: UserDefaults.didChangeNotification).sink { _ in
                   self.objectWillChange.send(self)
        }
    }

Code Block 
let url = ..... // your url
var warehouseOrders = .... // your array
private var cancelable: AnyCancellable?
private static let sessionProcessingQueue = DispatchQueue(label: "SessionProcessingQueue") 
private func loadWarehouseOrders() {
    cancelable = URLSession.shared.dataTaskPublisher(for: url)
      .subscribe(on: Self.sessionProcessingQueue)
      .map({
        print("\n $0.data: \($0.data)")
        return $0.data
        })
      .decode(type: WarehouseOrder.self, decoder: JSONDecoder())		// if you have a WarehouseOrder model
      .receive(on: DispatchQueue.main) // <-	 here is the problem, you are missing this 
      .sink(receiveCompletion: { (suscriberCompletion) in
        switch suscriberCompletion {
        case .finished:
					 // do something that you want to do when finished
          break
        case .failure(let error):
          print(error.localizedDescription)
        }
      }, receiveValue: { [weak self] (warehouseOrder) in
        self?.warehouseOrders.append(warehouseOrder) 
      })
  }
deinit {
    self.cancel()
}
func cancel(){
    cancelable.cancel()
}

Code Block swift
class ImageLoader: ObservableObject {
  private var cancellable: AnyCancellable?
  private var cache: ImageCache
  @Published var image: UIImage?
  private let url: URL
  init(url: URL, cache: ImageCache) {
    self.url = url
    self.cache = cache
  }
  deinit {
    cancellable?.cancel()
  }
  func load() {
    if let image = cache[url] {
      dispatchToMainThreadIfNeeded {
        self.image = image
      }
      return
    }
    cancellable = URLSession.shared.dataTaskPublisher(for: url)
      .map { UIImage(data: $0.data) }
      .handleEvents(receiveOutput: { [weak self] in self?.cache($0) })
      .replaceError(with: nil)
      .sink { value in
        self.image = value // Dispatch on main thread is not firing the publisher..
    }
  }
  func cancel() {
    cancellable?.cancel()
  }
  private func cache(_ image: UIImage?) {
    image.map { cache[url] = $0 }
  }
}

Code Block 
DispatchQueue.main.async {                    
	NotificationCenter.default.post()
}

Code Block 
DispatchQueue.main.async {                    
	NotificationCenter.default.post()
}

I got the error to go away by changing the .onAppear modifier to .task on a SwiftUI view observing a published property.

Below the navigation title modifier of the view.

.navigationTitle("Where you're at")

.task {
                // Fetch data from CloudKit here
                viewModel.fetchData()
            }

When adding @MainActor on whole viewModel class then those messages disappearing but if those messages still are and if that @MainActor no need, then how much important those messages?

Hi Max,

The warning is self explanatory so I will not explain whats happening over there. Coming to solution to dispatch the updates on Main Thread you can use @MainActor before the class keyword. This will automatically tell compiler to dispatch published updates on Main Thread. Thanks, Poonam