Push notifications (APNs + FCM) in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

Handling Notification Permissions Prompt

What happens when the following Swift code runs in an iOS app regarding push notification permissions?

iOS Swift

UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound, .badge]) { granted, error in
  if granted {
    DispatchQueue.main.async {
      UIApplication.shared.registerForRemoteNotifications()
    }
  }
}

A The app asks the user for permission to show alerts, play sounds, and update the badge, then registers for remote notifications if granted.

B The app immediately registers for remote notifications without asking the user for permission.

C The app only registers for local notifications and never asks for remote notification permission.

D The app requests permission but does not register for remote notifications even if permission is granted.

💡 Hint

Think about what requestAuthorization and registerForRemoteNotifications do.

The code first asks the user for permission to show notifications with alerts, sounds, and badges. If the user grants permission, the app then registers with APNs to receive remote notifications.

🧠 Conceptual

intermediate

Difference Between APNs and FCM

Which statement correctly describes the relationship between APNs and Firebase Cloud Messaging (FCM) in iOS push notifications?

A FCM directly delivers notifications to iOS devices without using APNs.

B APNs is a Google service that replaces FCM for iOS devices.

C FCM is a service that sends notifications to APNs, which then delivers them to iOS devices.

D APNs and FCM are two independent services that do not interact.

💡 Hint

Consider which service is Apple's and which is Google's, and how they work together.

Firebase Cloud Messaging (FCM) acts as a middleman that sends notifications to Apple Push Notification service (APNs), which then delivers them to iOS devices.

❓ lifecycle

advanced

App Behavior on Receiving Push Notification in Foreground

Given this delegate method in an iOS app, what will the user see when a push notification arrives while the app is open?

iOS Swift

func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
  completionHandler([.banner, .sound])
}

A The notification is silently received without any UI or sound.

B The notification banner and sound appear even though the app is in the foreground.

C Only the sound plays but no banner is shown.

D No notification is shown because the app is active.

💡 Hint

Think about what completionHandler controls in this method.

This delegate method lets the app decide how to present a notification when the app is active. Passing [.banner, .sound] shows a banner and plays a sound.

🔧 Debug

advanced

Why is the Device Token Not Received?

Consider this code snippet in an iOS app delegate. The app never receives a device token. What is the most likely cause?

iOS Swift

func application(_ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data) {
  print("Device token received")
}

func application(_ application: UIApplication, didFailToRegisterForRemoteNotificationsWithError error: Error) {
  print("Failed to register: \(error.localizedDescription)")
}

// Missing call to registerForRemoteNotifications() in app launch

A The app never called registerForRemoteNotifications(), so it never asked APNs for a device token.

B The device token is received but the print statement is incorrect.

C The app delegate methods are deprecated and no longer called.

D The app has no internet connection, so the token cannot be received.

💡 Hint

Check if the app requested remote notifications registration.

Without calling registerForRemoteNotifications(), the app does not ask APNs for a device token, so the delegate method is never called.

❓ navigation

expert

Navigating to a Specific Screen from a Push Notification

Which code snippet correctly navigates to a "MessagesViewController" when the user taps a push notification while the app is in background?

iOS Swift

func userNotificationCenter(_ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse, withCompletionHandler completionHandler: @escaping () -> Void) {
  let userInfo = response.notification.request.content.userInfo
  if let windowScene = UIApplication.shared.connectedScenes.first as? UIWindowScene,
     let rootVC = windowScene.windows.first?.rootViewController {
    // Navigation code here
  }
  completionHandler()
}

A

let messagesVC = MessagesViewController()
rootVC.navigationController?.pushViewController(messagesVC, animated: true)

B

let messagesVC = MessagesViewController()
rootVC.present(messagesVC, animated: true)

C

let messagesVC = MessagesViewController()
UIApplication.shared.keyWindow?.rootViewController?.present(messagesVC, animated: true)

D

let messagesVC = MessagesViewController()
if let nav = rootVC as? UINavigationController {
  nav.pushViewController(messagesVC, animated: true)
}

💡 Hint

Consider how to access the navigation controller from the root view controller.

To navigate properly, you must cast the root view controller to UINavigationController and then push the new view controller onto its stack.