SwiftUI: Environment Object Publisher doesn't send updates in onReceive

Question

I have a Network Monitor from where I want to receive notifications when status has changed.
Looks like this:

 final class NetworkMonitor: ObservableObject {
    let monitor = NWPathMonitor()
    let queue = DispatchQueue(label: "Monitor")

    static let shared = NetworkMonitor()

    @Published var status: NetworkStatus = .connected

    func start() {
        self.monitor.pathUpdateHandler = { [weak self] path in
            guard let self = self else { return }
            DispatchQueue.main.async {
                self.status = (path.status == .satisfied) ? .connected : .disconnected
            }
        }

        self.monitor.start(queue: self.queue)
    }
}

I create in Home a @StateObject of Network monitor and send it by an environment object.

struct HomeView: View {
    @StateObject var networkMonitor = NetworkMonitor()

    var body: some View {
        NavigationView {
            ContentView().environmentObject(networkMonitor)
        }
     }
 }

And I want in ContentView to receive any changes occur.

struct ContentView: View {
  @EnvironmentObject var networkMonitor: NetworkMonitor
  var body: some View {
     VStack {
         Text("Example")
     }.onReceive(self.networkMonitor.$status, perform: { status in
            print("onReceive \(status)") // <---- this doesn't trigger
       })
   }
}

I can't figure it out why whenever a change occurs in network status, the onReceive doesn't trigger.

EDIT: I am using shared instance to start monitoring in AppDelegate.

     func application(_: UIApplication, didFinishLaunchingWithOptions _: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        NetworkMonitor.shared.start()
}

Where are you calling start? Why is there a shared property (making it look like a singleton), but then you're creating an instance and passing it via envrionmentObject? Are you sure you aren't using shared somewhere else and using a different instance than what you have in your view? — jnpdx
– jnpdx, Commented Jun 22, 2021 at 19:29
Looks like what I suspected in the second half of my comment -- you're using a different instance in your AppDelegate than you are in your view. — jnpdx
– jnpdx, Commented Jun 22, 2021 at 19:33

jnpdx · Accepted Answer · 2021-06-22 19:38:26Z

5

You're using a different instance in your AppDelegate (shared) than you are in your HomeView (NetworkMonitor()).

Usually, when you use a singleton pattern, you want to make the init private so that you can avoid this mistake:

final class NetworkMonitor: ObservableObject {
    let monitor = NWPathMonitor()
    let queue = DispatchQueue(label: "Monitor")

    static let shared = NetworkMonitor()

    @Published var status: NetworkStatus = .connected

    private init() { } //<-- Here

    func start() {
        self.monitor.pathUpdateHandler = { [weak self] path in
            guard let self = self else { return }
            DispatchQueue.main.async {
                self.status = (path.status == .satisfied) ? .connected : .disconnected
            }
        }

        self.monitor.start(queue: self.queue)
    }
}

struct HomeView: View {
    @StateObject var networkMonitor = NetworkMonitor.shared //<-- Here

    var body: some View {
        NavigationView {
            ContentView().environmentObject(networkMonitor)
        }
     }
 }

edited Jun 22, 2021 at 19:38

answered Jun 22, 2021 at 19:35

jnpdx

53.3k7 gold badges91 silver badges123 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

user45723 Over a year ago

omg I'm so stupid 🤦‍♂️ thank you, you have brightened my day. I'll make this the accepted answear

Collectives™ on Stack Overflow

SwiftUI: Environment Object Publisher doesn't send updates in onReceive

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related