Push notifications (FCM) in Flutter - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Firebase Cloud Messaging (FCM)?

FCM is a free service by Google that lets apps send notifications and messages to users across Android, iOS, and web platforms.

beginner

Which Flutter package is commonly used to integrate FCM?

The firebase_messaging package is used to add Firebase Cloud Messaging support in Flutter apps.

intermediate

How do you request permission for notifications on iOS in Flutter?

Use FirebaseMessaging.instance.requestPermission() to ask the user for notification permissions on iOS devices.

beginner

What is a device token in FCM?

A device token is a unique ID that FCM uses to send notifications to a specific device.

intermediate

How can you handle a notification when the app is in the foreground?

Use FirebaseMessaging.onMessage.listen() to listen for messages and show custom UI or alerts when the app is open.

Which package do you add to your Flutter app to use Firebase Cloud Messaging?

A flutter_local_notifications

B firebase_messaging

C http

D firebase_auth

The firebase_messaging package is specifically designed to integrate FCM in Flutter apps.

What must you do on iOS before receiving push notifications?

A Request user permission for notifications

B Enable background fetch

C Install Google Play Services

D Nothing, it works automatically

iOS requires explicit user permission to show notifications, so you must request it.

What does the device token represent in FCM?

A A unique identifier for the device to receive messages

B The app version number

C The user's email address

D The Firebase project ID

The device token uniquely identifies the device for sending targeted notifications.

Which method listens for messages when the app is running in the foreground?

A FirebaseMessaging.subscribeToTopic()

B FirebaseMessaging.getInitialMessage()

C FirebaseMessaging.onMessage.listen()

D FirebaseMessaging.requestPermission()

onMessage.listen() handles incoming messages while the app is open.

What is the first step to set up FCM in a Flutter app?

A Request notification permission

B Write notification UI code

C Create a new Flutter widget

D Add firebase_messaging package and configure Firebase project

You must add the package and connect your app to Firebase before handling notifications.

Explain the steps to receive push notifications using FCM in a Flutter app.

Think about setup, permissions, and message handling.

Describe how to handle a notification when the app is open versus when it is closed.

Consider different app states and corresponding listeners.

Practice

1.

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

easy

A. To create user interfaces with Flutter widgets

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

C. To store user data locally on the device

D. To manage app navigation between screens

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

   Among the options, only sending push notifications matches FCM's main use.

3. Final Answer:

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

4. Quick Check:

   FCM purpose = send push notifications [OK]

Hint: FCM is for messaging, not UI or storage [OK]

Common Mistakes:

• Confusing FCM with UI or local storage
• Thinking FCM manages app navigation
• Assuming FCM only works when app is open

2.

Which Flutter code snippet correctly requests notification permissions on iOS using FirebaseMessaging?

FirebaseMessaging messaging = FirebaseMessaging.instance;
// What code requests permission?

easy

A. await messaging.requestPermission();

B. messaging.getToken();

C. FirebaseMessaging.onMessage.listen();

D. await messaging.subscribeToTopic('news');

Solution

1. Step 1: Identify permission request method

   The method to ask user permission for notifications is requestPermission().

2. Step 2: Match code snippet

   Only await messaging.requestPermission(); correctly requests permissions on iOS.

3. Final Answer:

   await messaging.requestPermission(); -> Option A

4. Quick Check:

   Permission request = requestPermission() [OK]

Hint: Permission request always uses requestPermission() method [OK]

Common Mistakes:

• Using getToken() to request permission
• Listening to messages instead of requesting permission
• Subscribing to topics does not request permission

3.

Given this Flutter code snippet, what will be printed when a push notification is received while the app is in the foreground?

FirebaseMessaging.onMessage.listen((RemoteMessage message) {
  print('Message received: ' + (message.notification?.title ?? 'No Title'));
});

medium

A. Message received: No Title

B. Message received: null

C. No output printed

D. Message received: [notification title]

Solution

1. Step 1: Understand onMessage listener

   This listener triggers when a notification arrives while app is open.

2. Step 2: Analyze print statement

   It prints 'Message received: ' plus the notification title if it exists, else 'No Title'.

3. Final Answer:

   Message received: [notification title] -> Option D

4. Quick Check:

   Foreground message prints notification title [OK]

Hint: ?.title returns title or null, ?? provides fallback [OK]

Common Mistakes:

• Ignoring null safety and expecting 'null' string
• Assuming no output if title is missing
• Confusing onMessage with background handlers

4.

Identify the error in this Flutter code snippet for handling FCM token retrieval:

FirebaseMessaging messaging = FirebaseMessaging.instance;
String? token = messaging.getToken();
print('Token: ' + token!);

medium

A. getToken() returns a Future, so it must be awaited

B. token cannot be null, so ! is unnecessary

C. FirebaseMessaging.instance is not initialized

D. print statement syntax is incorrect

Solution

1. Step 1: Check getToken() return type

   getToken() returns a Future, so it must be awaited to get the actual token.

2. Step 2: Identify missing await

   Code assigns Future to String? without await, causing error.

3. Final Answer:

   getToken() returns a Future, so it must be awaited -> Option A

4. Quick Check:

   Async methods need await to get values [OK]

Hint: Async calls must use await or then() [OK]

Common Mistakes:

• Ignoring async nature of getToken()
• Using ! without checking for null
• Assuming instance is uninitialized without reason

5.

You want to show a local notification when a push notification arrives while the app is in the foreground. Which approach correctly combines FirebaseMessaging with Flutter Local Notifications?

hard

A. Use FirebaseMessaging.subscribeToTopic to trigger local notifications automatically

B. Only use FirebaseMessaging.getToken to show notifications

C. Listen to FirebaseMessaging.onMessage and call local notification plugin to display notification

D. Call local notifications plugin inside FirebaseMessaging.getInitialMessage

Solution

1. Step 1: Understand foreground notification behavior

   FCM does not show notifications automatically when app is open; you must handle it manually.

2. Step 2: Combine onMessage with local notifications

   Listening to onMessage lets you detect incoming messages and then trigger local notifications to show alerts.

3. Step 3: Evaluate other options

   getToken only gets device token, subscribeToTopic manages topics, getInitialMessage handles app launch, none show notifications directly.

4. Final Answer:

   Listen to FirebaseMessaging.onMessage and call local notification plugin to display notification -> Option C

5. Quick Check:

   Foreground notifications need manual local notification trigger [OK]

Hint: Use onMessage + local notifications for foreground alerts [OK]

Common Mistakes:

• Expecting getToken to show notifications
• Thinking subscribeToTopic triggers UI automatically
• Using getInitialMessage for foreground notifications