Cloud Messaging (push notifications) in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

Handling Notification Click Behavior

You have a Firebase push notification that should open MainActivity when clicked. Which option correctly sets the PendingIntent to achieve this behavior?

Android Kotlin

val intent = Intent(this, MainActivity::class.java)
intent.flags = Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TASK
val pendingIntent = PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE)

A val pendingIntent = PendingIntent.getService(this, 0, intent, PendingIntent.FLAG_CANCEL_CURRENT or PendingIntent.FLAG_IMMUTABLE)

B val pendingIntent = PendingIntent.getBroadcast(this, 0, intent, PendingIntent.FLAG_ONE_SHOT or PendingIntent.FLAG_IMMUTABLE)

C val pendingIntent = PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE)

D val pendingIntent = PendingIntent.getActivity(this, 0, intent, 0)

💡 Hint

Use PendingIntent.getActivity for opening an activity on notification click.

Only PendingIntent.getActivity creates an intent to open an activity. Flags FLAG_UPDATE_CURRENT and FLAG_IMMUTABLE ensure the intent updates properly and is secure.

🧠 Conceptual

intermediate

Firebase Cloud Messaging Token Purpose

What is the main purpose of the Firebase Cloud Messaging (FCM) registration token in an Android app?

A It uniquely identifies the app instance to receive push notifications.

B It stores the user's login credentials securely.

C It manages the app's local database synchronization.

D It controls the app's UI theme settings remotely.

💡 Hint

Think about how Firebase knows where to send notifications.

The FCM token is a unique ID for each app installation, allowing Firebase to target push notifications to that specific device.

❓ lifecycle

advanced

Handling Notification in Foreground

When your Android app receives a Firebase push notification while in the foreground, which method should you override to handle the message and show a custom notification?

Android Kotlin

class MyFirebaseMessagingService : FirebaseMessagingService() {
  override fun onMessageReceived(remoteMessage: RemoteMessage) {
    // Your code here
  }
}

A Override onCreate(savedInstanceState: Bundle?) in Application class.

B Override onNewIntent(intent: Intent) in MainActivity.

C Override onStartCommand(intent: Intent?, flags: Int, startId: Int) in Service.

D Override onMessageReceived(remoteMessage: RemoteMessage) in FirebaseMessagingService.

💡 Hint

FirebaseMessagingService has a method called when messages arrive.

onMessageReceived is called for messages received while app is in foreground, allowing custom handling and notification display.

📝 Syntax

advanced

Correct Kotlin Syntax for Notification Channel Creation

Which Kotlin code snippet correctly creates a notification channel for Android 8.0+ devices?

A

val channel = NotificationChannel("channel_id", "Channel Name", 5)
val manager = getSystemService(NotificationManager::class.java)
manager.createNotificationChannel(channel)

B

val channel = NotificationChannel("channel_id", "Channel Name", NotificationManager.IMPORTANCE_DEFAULT)
val manager = getSystemService(NotificationManager::class.java)
manager.createNotificationChannel(channel)

C

val channel = NotificationChannel("channel_id", NotificationManager.IMPORTANCE_DEFAULT)
val manager = getSystemService(NotificationManager::class.java)
manager.createNotificationChannel(channel)

D

val channel = NotificationChannel("channel_id", "Channel Name")
val manager = getSystemService(NotificationManager::class.java)
manager.createNotificationChannel(channel)

💡 Hint

NotificationChannel constructor requires id, name, and importance.

The NotificationChannel constructor needs three parameters: id (String), name (String), and importance (int). Option B uses correct parameters and method calls.

🔧 Debug

expert

Debugging Missing Notifications on Android 13+

Your app targets Android 13 and above. Users report they do not receive push notifications. What is the most likely cause?

A The app lacks runtime POST_NOTIFICATIONS permission request.

B Notification channels are not created on Android 13.

C The Firebase token is expired and needs refreshing.

D The app is missing INTERNET permission in manifest.

💡 Hint

Android 13 introduced a new permission for notifications.

Starting Android 13, apps must request POST_NOTIFICATIONS permission at runtime to show notifications. Without it, notifications won't appear.

Practice

1. What is the main purpose of Firebase Cloud Messaging (FCM) in Android apps?

easy

A. To manage app permissions and settings

B. To store user data locally on the device

C. To send push notifications to users even when the app is closed

D. To create user interfaces with buttons and text

Solution

1. Step 1: Understand FCM's role

   Firebase Cloud Messaging is designed to send messages or notifications to users' devices.

2. Step 2: Identify the correct purpose

   It works even if the app is closed, keeping users updated with push notifications.

3. Final Answer:

   To send push notifications to users even when the app is closed -> Option C

4. Quick Check:

   FCM purpose = push notifications [OK]

Hint: Remember: FCM = push notifications, not UI or storage [OK]

Common Mistakes:

• Confusing FCM with local data storage
• Thinking FCM manages UI elements
• Assuming FCM controls app permissions

2. Which Kotlin class should you extend to handle incoming Firebase push messages in your Android app?

easy

A. FirebaseMessagingService

B. FirebaseDatabase

C. FirebaseAuth

D. FirebaseStorage

Solution

1. Step 1: Identify the service for message handling

   FirebaseMessagingService is the class designed to receive and handle push notifications.

2. Step 2: Exclude unrelated Firebase classes

   FirebaseDatabase, FirebaseAuth, and FirebaseStorage serve different purposes like data storage, authentication, and file storage.

3. Final Answer:

   FirebaseMessagingService -> Option A

4. Quick Check:

   Message handler class = FirebaseMessagingService [OK]

Hint: Use FirebaseMessagingService to receive messages [OK]

Common Mistakes:

• Choosing FirebaseDatabase for message handling
• Confusing FirebaseAuth with messaging
• Using FirebaseStorage instead of messaging service

3. Given the following Kotlin code snippet inside a FirebaseMessagingService subclass, what will be logged when a message is received?

override fun onMessageReceived(remoteMessage: RemoteMessage) {
    val title = remoteMessage.notification?.title ?: "No Title"
    val body = remoteMessage.notification?.body ?: "No Body"
    Log.d("FCM", "Title: $title, Body: $body")
}

medium

A. Title: No Title, Body: No Body if notification is null

B. App crashes if notification is null

C. Title and Body are always empty strings

D. Logs only the body, not the title

Solution

1. Step 1: Analyze null safety with Elvis operator

   The code uses ?: to provide default strings if notification or its fields are null.

2. Step 2: Understand logging behavior

   If notification is null, title and body become "No Title" and "No Body" respectively, so the log shows these defaults.

3. Final Answer:

   Title: No Title, Body: No Body if notification is null -> Option A

4. Quick Check:

   Elvis operator handles nulls = default text logged [OK]

Hint: Elvis operator ?: gives default when null [OK]

Common Mistakes:

• Assuming app crashes on null notification
• Thinking title/body become empty strings
• Believing only body is logged

4. You wrote this code to get the device token for FCM but it never logs the token. What is the error?

FirebaseMessaging.getInstance().token.addOnCompleteListener {
    if (!it.isSuccessful) return@addOnCompleteListener
    val token = it.result
    Log.d("FCM", "Token: $token")
}

medium

A. You need to call addOnSuccessListener instead of addOnCompleteListener

B. You forgot to add internet permission in AndroidManifest.xml

C. You must call getInstance() with context parameter

D. You should use getToken() instead of token property

Solution

1. Step 1: Check the API for token retrieval

   FirebaseMessaging.getInstance().getToken() is the correct method; there is no .token property.

2. Step 2: Verify other options

   Internet permission is needed to run, but the code won't compile due to undefined token property. getInstance() without context works, and addOnCompleteListener is correct.

3. Final Answer:

   You should use getToken() instead of token property -> Option D

4. Quick Check:

   No token property = use getToken() [OK]

Hint: Use getToken() method to fetch FCM token [OK]

Common Mistakes:

• Forgetting internet permission
• Thinking context is required for getInstance()
• Using wrong listener type for token retrieval

5. You want to send a push notification only to devices that have a specific user preference enabled. Which step is essential to implement this targeting correctly?

hard

A. Use FirebaseDatabase to store notifications and query them on the device

B. Send the device token to your server and filter tokens based on user preferences

C. Send notifications to all devices and let the app ignore unwanted ones

D. Use FirebaseAuth to authenticate users before sending notifications

Solution

1. Step 1: Understand device token role

   Device tokens uniquely identify devices to receive push notifications.

2. Step 2: Implement server-side filtering

   Send tokens to your server and filter them by user preferences before sending notifications.

3. Final Answer:

   Send the device token to your server and filter tokens based on user preferences -> Option B

4. Quick Check:

   Token + server filtering = targeted notifications [OK]

Hint: Always send tokens to server for targeted notifications [OK]

Common Mistakes:

• Sending notifications to all devices without filtering
• Using FirebaseDatabase instead of server filtering
• Confusing authentication with notification targeting