Using topics with Firebase Cloud Messaging - ios

Question

I am setting up Firebase Cloud Messaging to send notifications to an iOS app.
And I want to be able to send notifications, to all users who accepted to receive them.
After reading and experimenting quite a bit, my understanding is that (for my use case) I should set up some kind of general topic and then send each notification to this topic.
My question is: how to create a topic first, and then how to register (a client) to a topic in my iOS Swift app?
Though I tried to browse the net for info on that, I did not find much.
For information, I am using Xcode Version 10.1, iOS 12.1 and Swift 4.2.

Answer 1

Step 1: Setting Up Firebase
If you have yet to add Firebase to your project, it's all documented here:
https://firebase.google.com/docs/ios/setup
You will need to start the configuration of Firebase. For my project, I started the configuration in the AppDelegate upon app start.
class AppDelegate: UIResponder, UIApplicationDelegate, MessagingDelegate {
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
FirebaseApp.configure()
Messaging.messaging().delegate = self
...
}
...
}
Step 2: Requesting Authorization
Assuming you have all the APNs Authentication Key/Certificates configured on your Apple Developer Portal and Firebase Cloud Messaging settings,
https://developer.apple.com/account/ios/certificate/
https://console.firebase.google.com/u/0/project/FIREBASE_PROJECT_NAME/settings/cloudmessaging/ios:APP_BUNDLE_ID
Next, you will need to request authorization for Push Notifications on the device. I've placed this in one of the first few UIViewControllers my project.
class FirstViewController: UIViewController {
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .badge, .sound], completionHandler: { (success, error) in
guard success else { return }
UIApplication.shared.registerForRemoteNotifications()
})
}
}
Step 3: Device Token
Upon registering for remote notification in step 2 with:
UIApplication.shared.registerForRemoteNotifications()
You will need to implement this delegate function in your AppDelegate:
class AppDelegate: UIResponder, UIApplicationDelegate, MessagingDelegate {
...
func application(_ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data) {
Messaging.messaging().apnsToken = deviceToken.reduce("", {$0 + String(format: "%02X", $1)})
}
...
}
Do note that the deviceToken received is in NSData, and the apnsToken required by Firebase is in String.
Step 4: Topic Subscription
Remember the delegate reference we set to AppDelegate in step 1?
Messaging.messaging().delegate = self
You will need to implement its delegate function to let the app know that it Firebase did receive the token and it is ready to subscribe to a topic.
class AppDelegate: UIResponder, UIApplicationDelegate, MessagingDelegate {
...
func messaging(_ messaging: Messaging, didReceiveRegistrationToken fcmToken: String) {
Messaging.messaging().subscribe(toTopic: "/topics/example")
}
...
}
Step 5: Validation
One simple way to check if your app has successfully subscribed to a topic is to send a push notification via Firebase Console.
https://console.firebase.google.com/u/0/project/FIREBASE_PROJECT_NAME/notification