Push notifications (FCM) in Flutter - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

Handling Notification Tap Behavior

What happens when a user taps a push notification in a Flutter app configured with Firebase Cloud Messaging (FCM) using the following code snippet?

Flutter

FirebaseMessaging.onMessageOpenedApp.listen((RemoteMessage message) {
  Navigator.pushNamed(context, '/details', arguments: message.data);
});

A The app crashes due to missing context.

B The app closes immediately without any navigation.

C The app navigates to the '/details' screen passing the notification data as arguments.

D The app shows a toast message but does not navigate.

💡 Hint

Think about what the listener for onMessageOpenedApp is designed to do.

The onMessageOpenedApp listener triggers when the user taps a notification. The code navigates to the '/details' screen passing the notification data.

🧠 Conceptual

intermediate

FCM Token Usage

What is the main purpose of the FCM device token in a Flutter app using Firebase Cloud Messaging?

A It stores the user's login credentials securely.

B It uniquely identifies the device to send targeted push notifications.

C It is used to style the notification appearance on the device.

D It tracks the number of notifications received by the device.

💡 Hint

Think about how Firebase knows which device to send a notification to.

The FCM token is a unique identifier for each device, allowing Firebase to send notifications specifically to that device.

❓ lifecycle

advanced

App State and Notification Handling

Consider a Flutter app with FCM configured. Which callback handles messages received when the app is in the foreground?

A FirebaseMessaging.onBackgroundMessage

B FirebaseMessaging.getInitialMessage

C FirebaseMessaging.onMessageOpenedApp

D FirebaseMessaging.onMessage

💡 Hint

Foreground means the app is open and visible to the user.

onMessage is called when the app is open and running in the foreground and receives a notification.

🔧 Debug

advanced

Debugging Missing Notifications

A Flutter app with FCM does not receive notifications when the app is killed (not running). What is a likely cause?

A The onBackgroundMessage handler is not registered or missing.

B The Firebase project is not linked to the app.

C The app does not have internet permission in AndroidManifest.xml.

D The notification payload is missing the title field.

💡 Hint

Background messages require a special handler to be registered.

To receive messages when the app is terminated, onBackgroundMessage must be set up properly.

📝 Syntax

expert

Correct Syntax for Background Message Handler

Which of the following is the correct way to define and register a background message handler in Flutter with FCM?

Flutter

Future<void> _firebaseMessagingBackgroundHandler(RemoteMessage message) async {
  // Handle background message
}

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  FirebaseMessaging.onBackgroundMessage(_firebaseMessagingBackgroundHandler);
  runApp(MyApp());
}

A

Future<void> _firebaseMessagingBackgroundHandler(RemoteMessage message) async {
  // Handle background message
}

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  FirebaseMessaging.onBackgroundMessage(_firebaseMessagingBackgroundHandler);
  runApp(MyApp());
}

B

void _firebaseMessagingBackgroundHandler(RemoteMessage message) {
  // Handle background message
}

void main() {
  FirebaseMessaging.onBackgroundMessage(_firebaseMessagingBackgroundHandler);
  runApp(MyApp());
}

C

Future<void> _firebaseMessagingBackgroundHandler() async {
  // Handle background message
}

void main() {
  FirebaseMessaging.onBackgroundMessage(_firebaseMessagingBackgroundHandler);
  runApp(MyApp());
}

D

Future<void> _firebaseMessagingBackgroundHandler(RemoteMessage message) async {
  // Handle background message
}

void main() {
  runApp(MyApp());
  FirebaseMessaging.onBackgroundMessage(_firebaseMessagingBackgroundHandler);
}

💡 Hint

The handler must be async, accept RemoteMessage, and be registered before runApp.

The background handler must be a top-level async function accepting RemoteMessage. It must be registered before runApp is called.