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
Hub.subscribe(HubChannel hubChannel, HubSubscriber hubSubscriber) is used to listen for messages that have been dispatched. Additionally, you can pass a HubEventFilter in the overloaded subscribe method to further filter Hub events. You can add multiple listeners to your application for different combinations of channels/filters to listen for.
Amplify.Hub.subscribe(HubChannel.AUTH, hubEvent -> { if (hubEvent.getName().equals(InitializationStatus.SUCCEEDED.toString())) { Log.i("AuthQuickstart", "Auth successfully initialized"); } else if (hubEvent.getName().equals(InitializationStatus.FAILED.toString())){ Log.i("AuthQuickstart", "Auth failed to succeed"); } else { switch (AuthChannelEventName.valueOf(hubEvent.getName())) { case SIGNED_IN: Log.i("AuthQuickstart", "Auth just became signed in."); break; case SIGNED_OUT: Log.i("AuthQuickstart", "Auth just became signed out."); break; case SESSION_EXPIRED: Log.i("AuthQuickstart", "Auth session just expired."); break; case USER_DELETED: Log.i("AuthQuickstart", "User has been deleted."); break; default: Log.w("AuthQuickstart", "Unhandled Auth Event: " + AuthChannelEventName.valueOf(hubEvent.getName())); break; } } });Amplify.Hub.subscribe(HubChannel.AUTH) { event -> when (event.name) { InitializationStatus.SUCCEEDED.toString() -> Log.i("AuthQuickstart", "Auth successfully initialized") InitializationStatus.FAILED.toString() -> Log.i("AuthQuickstart", "Auth failed to succeed") else -> when (AuthChannelEventName.valueOf(event.name)) { AuthChannelEventName.SIGNED_IN -> Log.i("AuthQuickstart", "Auth just became signed in") AuthChannelEventName.SIGNED_OUT -> Log.i("AuthQuickstart", "Auth just became signed out") AuthChannelEventName.SESSION_EXPIRED -> Log.i("AuthQuickstart", "Auth session just expired") AuthChannelEventName.USER_DELETED -> Log.i("AuthQuickstart", "User has been deleted") else -> Log.w("AuthQuickstart", "Unhandled Auth Event: ${event.name}") } }}Amplify.Hub.subscribe(HubChannel.AUTH).collect { when (it.name) { InitializationStatus.SUCCEEDED.toString() -> Log.i("AuthQuickstart", "Auth successfully initialized") InitializationStatus.FAILED.toString() -> Log.i("AuthQuickstart", "Auth failed to succeed") else -> when (AuthChannelEventName.valueOf(it.name)) { AuthChannelEventName.SIGNED_IN -> Log.i("AuthQuickstart", "Auth just became signed in.") AuthChannelEventName.SIGNED_OUT -> Log.i("AuthQuickstart", "Auth just became signed out.") AuthChannelEventName.SESSION_EXPIRED -> Log.i("AuthQuickstart", "Auth session just expired.") AuthChannelEventName.USER_DELETED -> Log.i("AuthQuickstart", "User has been deleted.") } }}RxAmplify.Hub.on(HubChannel.AUTH) .map(HubEvent::getName) .subscribe(name -> { if (name.equals(InitializationStatus.SUCCEEDED.toString())) { Log.i("AuthQuickstart", "Auth successfully initialized"); return; } else if (name.equals(InitializationStatus.FAILED.toString())) { Log.i("AuthQuickstart", "Auth failed to succeed"); return; } switch (AuthChannelEventName.valueOf(name)) { case SIGNED_IN: Log.i("AuthQuickstart", "Auth just became signed in."); break; case SIGNED_OUT: Log.i("AuthQuickstart", "Auth just became signed out."); break; case SESSION_EXPIRED: Log.i("AuthQuickstart", "Auth session just expired."); break; case USER_DELETED: Log.i("AuthQuickstart", "User has been deleted."); break; default: Log.w("AuthQuickstart", "Unhandled Auth Event: " + AuthChannelEventName.valueOf(name)); break; } });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 (ex: changing Activities or Fragments), as well as to avoid any memory leaks.
// Subscribe to Hub Auth events and capture the returned SubscriptionTokenSubscriptionToken subscriptionToken = Amplify.Hub.subscribe(HubChannel.AUTH, event -> { handleAuthEvent(event);});
// Unsubscribe by passing the captured SubscriptionTokenAmplify.Hub.unsubscribe(subscriptionToken);// Subscribe to Hub Auth events and capture the returned SubscriptionTokenval subscriptionToken = Amplify.Hub.subscribe(HubChannel.AUTH) { event -> handleAuthEvent(event)}
// Unsubscribe by passing the captured SubscriptionToken Amplify.Hub.unsubscribe(subscriptionToken)