Push notification integration in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Push Notification Tokens

What is the primary purpose of a push notification token in mobile apps?

A It schedules the notification delivery time

B It stores the content of the notification message

C It encrypts the notification data before sending

D It uniquely identifies a device to receive push notifications

💡 Hint

Think about how the server knows where to send the notification.

A push notification token is a unique identifier assigned to a device by the notification service. It tells the server exactly which device should receive the notification.

❓ ui_behavior

intermediate

Notification Permission Request Behavior

When should a mobile app request permission from the user to send push notifications?

A Immediately when the app launches for the first time

B After the user has received at least one notification

C Only after explaining the benefits of notifications to the user

D Only if the user navigates to the settings screen

💡 Hint

Consider user experience and avoiding annoying pop-ups.

Requesting permission after explaining benefits helps users understand why notifications are useful, increasing the chance they allow them.

❓ lifecycle

advanced

Handling Notifications When App is in Background

What happens when a push notification arrives while the app is in the background on a mobile device?

A The notification is shown in the device's notification center without opening the app

B The app automatically opens and displays the notification content

C The notification is ignored until the app is opened again

D The app crashes if it tries to process the notification in the background

💡 Hint

Think about how notifications appear outside the app.

When the app is in the background, the system shows the notification in the notification center. The app does not open automatically.

❓ navigation

advanced

Navigating After Notification Tap

Which approach correctly handles navigation when a user taps a push notification to open the app?

HLD

function onNotificationTap(notification) {
  if (notification.data && notification.data.screen) {
    navigateTo(notification.data.screen);
  } else {
    navigateTo('Home');
  }
}

A Ignore notification data and reload the current screen

B Check notification data for target screen and navigate accordingly

C Always navigate to the Home screen regardless of notification content

D Close the app immediately after tapping the notification

💡 Hint

Think about how to direct users to relevant content from notifications.

Using notification data to decide navigation ensures users see the content related to the notification they tapped.

🔍 Analysis

expert

Debugging Missing Push Notifications

A developer notices users do not receive push notifications on Android devices. Which issue below is the most likely cause?

A The app did not register the device token with the push notification service

B The app uses HTTPS instead of HTTP for sending notifications

C The notification payload is missing the title field

D The app requested notification permission too late after launch

💡 Hint

Without a device token, the server cannot send notifications to the device.

If the device token is not registered, the push service does not know where to send notifications, so users won't receive them.

Practice

1. What is the main purpose of integrating push notifications in a mobile app?

easy

A. To keep users updated even when the app is closed

B. To increase app size significantly

C. To slow down the app performance

D. To disable user interaction

Solution

1. Step 1: Understand push notification purpose

   Push notifications are messages sent to users to keep them informed or engaged.

2. Step 2: Identify correct purpose in options

   Only To keep users updated even when the app is closed correctly states that notifications keep users updated even when app is closed.

3. Final Answer:

   To keep users updated even when the app is closed -> Option A

4. Quick Check:

   Push notifications = keep users updated [OK]

Hint: Push notifications inform users outside the app [OK]

Common Mistakes:

• Thinking notifications increase app size
• Believing notifications slow app down
• Assuming notifications disable interaction

2. Which code snippet correctly requests user permission for push notifications in a mobile app?

easy

A. requestNotificationPermission();

B. enablePushNotifications();

C. askUserForNotificationPermission();

D. requestPermissionForNotifications();

Solution

1. Step 1: Identify standard permission request method

   Common method names include 'requestPermissionForNotifications' to ask user consent.

2. Step 2: Compare options for correct syntax

   requestPermissionForNotifications(); uses a clear, standard naming pattern for requesting permission.

3. Final Answer:

   requestPermissionForNotifications(); -> Option D

4. Quick Check:

   Permission request method = requestPermissionForNotifications() [OK]

Hint: Look for method names starting with 'requestPermission' [OK]

Common Mistakes:

• Using method names that don't request permission
• Confusing enabling notifications with requesting permission
• Using non-standard or undefined method names

3. Given this code snippet handling a push notification:

onNotificationReceived(notification) {
  if (notification.type === 'message') {
    showAlert(notification.title);
  }
}

What happens when a notification with type 'message' arrives?

medium

A. An alert with the notification title is shown

B. The notification is ignored

C. The app crashes due to missing handler

D. A log is printed but no alert

Solution

1. Step 1: Analyze the notification type check

   The code checks if notification.type equals 'message'.

2. Step 2: Understand the action on matching type

   If true, it calls showAlert with notification.title, displaying an alert.

3. Final Answer:

   An alert with the notification title is shown -> Option A

4. Quick Check:

   Type 'message' triggers alert display [OK]

Hint: Check condition and action inside notification handler [OK]

Common Mistakes:

• Assuming notification is ignored
• Thinking app crashes without error
• Confusing logging with alert display

4. Identify the error in this push notification handler code:

function handleNotification(notification) {
  if notification.isRead = false {
    displayNotification(notification);
  }
}

medium

A. Missing semicolon after function declaration

B. Using assignment '=' instead of comparison '==' in if condition

C. Incorrect function name 'handleNotification'

D. Notification object missing required fields

Solution

1. Step 1: Check the if condition syntax

   The condition uses '=' which assigns value instead of comparing.

2. Step 2: Identify correct comparison operator

   It should use '==' or '===' to compare values, not '='.

3. Final Answer:

   Using assignment '=' instead of comparison '==' in if condition -> Option B

4. Quick Check:

   Use '==' for comparison, not '=' [OK]

Hint: Remember '=' assigns, '==' compares in conditions [OK]

Common Mistakes:

• Confusing assignment and comparison operators
• Ignoring syntax errors in if statements
• Assuming function name causes error

5. You want to send a push notification only if the user has granted permission and the app is in background. Which logic correctly implements this?

hard

A. if (userPermissionGranted && appState !== 'background') { sendPushNotification(); }

B. if (userPermissionGranted || appState === 'background') { sendPushNotification(); }

C. if (userPermissionGranted && appState === 'background') { sendPushNotification(); }

D. if (!userPermissionGranted && appState === 'background') { sendPushNotification(); }

Solution

1. Step 1: Understand conditions for sending notification

   Notification should send only if permission is granted AND app is in background.

2. Step 2: Evaluate logical operators in options

   if (userPermissionGranted && appState === 'background') { sendPushNotification(); } uses '&&' (AND) correctly to check both conditions.

3. Final Answer:

   if (userPermissionGranted && appState === 'background') { sendPushNotification(); } -> Option C

4. Quick Check:

   Use AND (&&) to require both conditions [OK]

Hint: Use AND (&&) to combine required conditions [OK]

Common Mistakes:

• Using OR (||) instead of AND (&&)
• Negating permission incorrectly
• Checking wrong app state