Hub

Amplify has a local eventing system called Hub. It is a lightweight implementation of Publisher-Subscriber pattern, and is used to share data between modules and components in your app. Amplify uses Hub for different categories to communicate with one another when specific events occur, such as authentication events like a user sign-in or notification of a file download.

Working with the API

Listening for messages

You can use Amplify.Hub.listen(to: HubChannel) {...} (listener) or Amplify.Hub.publisher(for: HubChannel).sink {...} (Combine) to listen for messages that have been dispatched. Additionally, you can pass isIncluded: HubFilter or eventName: HubPayloadEventName to the listen method to further filter Hub events. You can add multiple listeners to your application for different combinations of channels, filters, and events.

1override func viewDidLoad() {
2    super.viewDidLoad()
3    // Do any additional setup after loading the view.
4
5    // Assumes `unsubscribeToken` is declared as an instance variable in your view
6    unsubscribeToken = Amplify.Hub.listen(to: .auth) { payload in
7        switch payload.eventName {
8        case HubPayload.EventName.Auth.signedIn:
9            print("User signed in")
10            // Update UI
11
12        case HubPayload.EventName.Auth.sessionExpired:
13            print("Session expired")
14            // Re-authenticate the user
15
16        case HubPayload.EventName.Auth.signedOut:
17            print("User signed out")
18            // Update UI
19
20        case HubPayload.EventName.Auth.userDeleted:
21            print("User deleted")
22            // Update UI
23
24        default:
25            break
26        }
27    }
28}

Stop Listening

Hub provides a way to stop listening for messages. This is useful if you no longer need to receive messages in your application flow.

1// Assumes `unsubscribeToken` references the token
2// returned by Amplify.Hub.listen(...)
3Amplify.Hub.removeListener(unsubscribeToken)