Push notifications (APNs + FCM) in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to request user permission for push notifications in Swift.

iOS Swift

UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound, [1]]) { granted, error in
    if granted {
        print("Permission granted")
    }
}

Drag options to blanks, or click blank then click option'

A.calendar

B.location

C.badge

D.contacts

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing unrelated options like location or contacts which are not notification permissions.

The .badge option allows the app to show badge counts on the app icon, which is part of push notification permissions.

2fill in blank

medium

Complete the code to register for remote notifications after permission is granted.

iOS Swift

DispatchQueue.main.async {
    UIApplication.shared.[1]()
}

Drag options to blanks, or click blank then click option'

AregisterUserNotificationSettings

BregisterForRemoteNotifications

CbeginBackgroundTask

DopenSettingsURLString

Attempts:

3 left

💡 Hint

Common Mistakes

Using deprecated or unrelated methods like registerUserNotificationSettings.

The method registerForRemoteNotifications() tells iOS to start receiving push notifications from APNs.

3fill in blank

hard

Fix the error in the delegate method to receive the device token for APNs.

iOS Swift

func application(_ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken [1]: Data) {
    let tokenParts = [2].map { data in String(format: "%02.2hhx", data) }
    let token = tokenParts.joined()
    print("Device Token: \(token)")
}

Drag options to blanks, or click blank then click option'

AdeviceToken

BnotificationToken

CtokenData

DpushToken

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect parameter names causes the delegate method not to be called.

The parameter name must be deviceToken to match the delegate method signature exactly.

4fill in blank

hard

Fill both blanks to create a dictionary payload for Firebase Cloud Messaging (FCM) with a notification title and body.

iOS Swift

let message: [String: Any] = [
    "notification": [
        "title": [1],
        "body": [2]
    ]
]

Drag options to blanks, or click blank then click option'

A"Hello"

B"Welcome to the app!"

C"Goodbye"

D"Error occurred"

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-string values or forgetting quotes around strings.

The notification dictionary requires string values for title and body. Here, "Hello" is the title and "Welcome to the app!" is the body.

5fill in blank

hard

Fill all three blanks to handle receiving a push notification in the app delegate and print its content.

iOS Swift

func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
    let userInfo = notification.[1].request.content.[2]
    print("Received notification with info: \(userInfo)")
    completionHandler([3])
}

Drag options to blanks, or click blank then click option'

Adelegate

Bcontent

C[.alert, .sound]

DuserInfo

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong property names or forgetting to call the completion handler.

The notification parameter has a request property, which has content. The content contains userInfo dictionary with the notification data. The completion handler is called with presentation options like [.alert, .sound] to show the notification while the app is in foreground.

Practice

1. What is the primary purpose of APNs in iOS push notifications?

easy

A. To store app data locally

B. To manage user authentication

C. To deliver push notifications to iOS devices

D. To create user interface elements

Solution

1. Step 1: Understand APNs role

   APNs stands for Apple Push Notification service and is designed to send notifications to iOS devices.

2. Step 2: Differentiate from other services

   It does not handle authentication, data storage, or UI creation, only notification delivery.

3. Final Answer:

   To deliver push notifications to iOS devices -> Option C

4. Quick Check:

   APNs = notification delivery [OK]

Hint: APNs is Apple's service for sending notifications [OK]

Common Mistakes:

• Confusing APNs with authentication services
• Thinking APNs manages app data
• Assuming APNs creates UI elements

2. Which Swift code snippet correctly requests permission for push notifications?

easy

A. UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound]) { granted, error in }

B. UNUserNotificationCenter.requestAuthorization(options: [.alert])

C. UNNotificationCenter.current().requestPermission()

D. UserNotificationCenter.requestAuthorization(options: [.badge])

Solution

1. Step 1: Identify correct class and method

   The correct class is UNUserNotificationCenter and the method is requestAuthorization with options and completion handler.

2. Step 2: Check syntax correctness

   UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound]) { granted, error in } uses the correct syntax with options array and closure parameters.

3. Final Answer:

   UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound]) { granted, error in } -> Option A

4. Quick Check:

   Correct class and method = UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound]) { granted, error in } [OK]

Hint: Use UNUserNotificationCenter.current().requestAuthorization with options [OK]

Common Mistakes:

• Using wrong class names like UNNotificationCenter
• Omitting the completion handler closure
• Incorrect method names like requestPermission

3. Given this Swift code snippet, what will be printed if the device token is successfully received?

func application(_ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data) {
    let tokenParts = deviceToken.map { data in String(format: "%02.2hhx", data) }
    let token = tokenParts.joined()
    print("Device Token: \(token)")
}

medium

A. Device Token: nil

B. Device Token:

C. Device Token: deviceToken

D. Device Token: [data]

Solution

1. Step 1: Understand deviceToken processing

   The deviceToken is converted byte-by-byte to a hexadecimal string representation.

2. Step 2: Analyze print output

   The print statement outputs "Device Token: " followed by the joined hex string, not the raw data or nil.

3. Final Answer:

   Device Token: <hexadecimal string> -> Option B

4. Quick Check:

   Device token converted to hex string = Device Token: <hexadecimal string> [OK]

Hint: Device token is hex string printed, not raw data [OK]

Common Mistakes:

• Expecting raw Data object printed
• Assuming deviceToken is nil
• Printing deviceToken without conversion

4. Identify the error in this Swift code snippet for registering remote notifications:

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

medium

A. Incorrect options array syntax

B. Missing call to UNUserNotificationCenter.current().delegate assignment

C. registerForRemoteNotifications() should be called outside DispatchQueue.main.async

D. No error, code is correct

Solution

1. Step 1: Verify permission request syntax

   UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .badge, .sound]) { granted, error in ... } uses correct class, method, options, and completion handler.

2. Step 2: Confirm registration call

   DispatchQueue.main.async ensures UIApplication.shared.registerForRemoteNotifications() runs on the main thread, which is correct practice.

3. Final Answer:

   No error, code is correct -> Option D

4. Quick Check:

   Standard registration flow followed correctly [OK]

Hint: This code correctly requests permission and registers for remote notifications [OK]

Common Mistakes:

• Thinking UNUserNotificationCenter delegate is required inside this registration function
• Claiming incorrect options array syntax
• Believing registerForRemoteNotifications should avoid DispatchQueue.main.async

5. You want to send a push notification to an iOS app using Firebase Cloud Messaging (FCM). Which step is essential to link APNs with FCM for this to work correctly?

hard

A. Upload the APNs authentication key or certificates to the Firebase Console

B. Enable Background Modes in Xcode without any APNs setup

C. Register the device token only with APNs, ignoring FCM

D. Use only APNs without configuring Firebase

Solution

1. Step 1: Understand FCM and APNs integration

   FCM requires APNs credentials to send notifications to iOS devices through Apple's service.

2. Step 2: Identify required configuration

   You must upload the APNs authentication key or certificates to Firebase Console to enable this link.

3. Final Answer:

   Upload the APNs authentication key or certificates to the Firebase Console -> Option A

4. Quick Check:

   APNs key upload to Firebase = Upload the APNs authentication key or certificates to the Firebase Console [OK]

Hint: Upload APNs key to Firebase to enable iOS push via FCM [OK]

Common Mistakes:

• Skipping APNs key upload to Firebase
• Relying only on Background Modes without APNs
• Ignoring FCM device token registration