I have an Updater class that uses Combine to check a state then update another state. If I initialize the Updater in a view it works fine but it is initilized again each time the View is redrawn. If I initialize the Updater outside the View the Combine process isn’t called when the state updates, i.e. sink is only called one, not when firstCount is updated.

The Updater class that uses Combine:

class Updater {
  private var cancellables = Set<AnyCancellable>()

  func setup(appState: AppState) {
    CurrentValueSubject<Int, Never>(appState.firstCount)
      .map {
        $0 * 10
      }
      .sink { value in
        print("Sink (value)")
        DispatchQueue.main.async {
          appState.resultCount = value
        }
      }
      .store(in: &cancellables)
  }
}

The State:

@Observable class AppState {
  var firstCount: Int = 0
  var resultCount: Int = 0
}

The App struct that initializes the BackgroundTask:

@main
struct TestCombineInViewApp: App {
  var appState: AppState = AppState()
  private let updater: Updater

  init() {
    let appState = AppState()
    self.appState = appState

    updater = Updater()
    updater.setup(appState: appState)
  }

  var body: some Scene {
    WindowGroup {
      ContentView(appState: appState)
    }
  }
}

The view:

struct ContentView: View {
  @State private var appState: AppState
  init(appState: AppState) {
    self.appState = appState
  }

  var body: some View {
    VStack {
      Text("first Count: (appState.firstCount)")
      Text("Result Count: (appState.resultCount)")
      Button {
        appState.firstCount += 1
      } label: {
        Text("Plus")
      }
    }
  }
}

The resultCount should be updated each time firstCount is updated via the Button.

I’m guessing that Cancellables must be created inside the View hierarchy, but I don’t really follow how this works.