Push notifications with FCM in React Native - UI Render Trace

Component - Push notifications with FCM

This component shows how a React Native app integrates Firebase Cloud Messaging (FCM) to receive push notifications. It listens for messages and displays a simple alert when a notification arrives.

Widget Tree

App (Functional Component)
├─ View (Container)
│  ├─ Text (Title: "FCM Push Notifications")
│  └─ Button (Request Permission)
└─ Alert (System Alert on notification)

The root is the App functional component. Inside it, a View container holds a Text title and a Button to request notification permission. When a push notification arrives, a system Alert pops up to show the message.

Render Trace - 5 Steps

Step 1: App

Step 2: View

Step 3: Text

Step 4: Button

Step 5: Alert (System)

State Change - Re-render

Trigger:User presses 'Request Permission' button and grants notification permission

Before

No permission granted, no notifications received

→

After

Permission granted, app listens for FCM messages

Re-renders:App component re-renders to reflect permission status if needed; listeners active in background

UI Quiz - 3 Questions

What happens when the user presses the 'Request Permission' button?

A The app asks the user to allow notifications

B The app sends a push notification immediately

C The app closes

D Nothing happens

Key Insight

In React Native, integrating push notifications with FCM requires setting up listeners inside a functional component using useEffect. The UI should clearly prompt users to grant permission and handle incoming messages gracefully, often by showing alerts or updating the UI. Keeping the layout simple and accessible helps users understand and interact with notifications.

Practice

1. What is the main purpose of Firebase Cloud Messaging (FCM) in a React Native app?

easy

A. To create UI components

B. To store user data locally

C. To send push notifications to the app users

D. To manage app navigation

Solution

1. Step 1: Understand FCM's role

   FCM is a service designed to send push notifications to apps.

2. Step 2: Compare options

   Only To send push notifications to the app users describes sending push notifications, which is FCM's main purpose.

3. Final Answer:

   To send push notifications to the app users -> Option C

4. Quick Check:

   FCM = Push notifications [OK]

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

Common Mistakes:

• Confusing FCM with local data storage
• Thinking FCM manages UI or navigation
• Assuming FCM is for database operations

2. Which React Native Firebase method is used to get the device token for FCM push notifications?

easy

A. messaging().requestPermission()

B. messaging().getToken()

C. messaging().sendMessage()

D. messaging().subscribeToTopic()

Solution

1. Step 1: Identify token retrieval method

   The method to get the device token is messaging().getToken().

2. Step 2: Eliminate other options

   requestPermission() asks user permission, sendMessage() sends messages, subscribeToTopic() subscribes to topics.

3. Final Answer:

   messaging().getToken() -> Option B

4. Quick Check:

   Get token = getToken() [OK]

Hint: Get token with getToken(), not requestPermission() [OK]

Common Mistakes:

• Using requestPermission() to get token
• Confusing sendMessage() with token retrieval
• Mixing subscribeToTopic() with token methods

3. What will be the output of this code snippet in a React Native app using FCM?

import messaging from '@react-native-firebase/messaging';

async function getToken() {
  const token = await messaging().getToken();
  console.log(token);
}

getToken();

medium

A. Logs the device's FCM token string to the console

B. Throws a syntax error due to missing await

C. Logs 'undefined' because getToken() returns nothing

D. Throws a runtime error because messaging() is undefined

Solution

1. Step 1: Analyze async function behavior

   The function awaits messaging().getToken(), which returns the device token string.

2. Step 2: Understand console.log output

   It logs the token string, not undefined or error, assuming messaging is imported correctly.

3. Final Answer:

   Logs the device's FCM token string to the console -> Option A

4. Quick Check:

   getToken() returns token string [OK]

Hint: Await getToken() to get token string, then log it [OK]

Common Mistakes:

• Forgetting await causing Promise logged
• Assuming getToken() returns undefined
• Not importing messaging correctly

4. You wrote this code to request permission for notifications but it doesn't work as expected:

import messaging from '@react-native-firebase/messaging';

messaging().requestPermission();

What is the likely problem?

medium

A. requestPermission() is not a valid method

B. You need to import notifications instead of messaging

C. You must call getToken() before requestPermission()

D. You forgot to await the requestPermission() call

Solution

1. Step 1: Check async method usage

   requestPermission() returns a Promise and should be awaited to complete permission request.

2. Step 2: Identify missing await effect

   Without await, the permission request may not finish before next steps, causing unexpected behavior.

3. Final Answer:

   You forgot to await the requestPermission() call -> Option D

4. Quick Check:

   Await async calls like requestPermission() [OK]

Hint: Always await async permission requests [OK]

Common Mistakes:

• Not awaiting async permission calls
• Thinking requestPermission() is invalid
• Calling getToken() before permission

5. You want to send a push notification only if the user has granted permission. Which code snippet correctly checks permission and then gets the FCM token in React Native?

hard

A. const authStatus = await messaging().requestPermission();
if (authStatus === messaging.AuthorizationStatus.AUTHORIZED) {
const token = await messaging().getToken();
console.log(token);
}

B. const token = await messaging().getToken();
if (token) {
await messaging().requestPermission();
console.log(token);
}

C. await messaging().getToken();
await messaging().requestPermission();
console.log('Permission and token done');

D. messaging().requestPermission();
messaging().getToken();
console.log('Permissions requested and token fetched');

Solution

1. Step 1: Check permission before token

   const authStatus = await messaging().requestPermission(); if (authStatus === messaging.AuthorizationStatus.AUTHORIZED) { const token = await messaging().getToken(); console.log(token); } requests permission and checks if authorized before getting token.

2. Step 2: Verify async and order correctness

   const authStatus = await messaging().requestPermission(); if (authStatus === messaging.AuthorizationStatus.AUTHORIZED) { const token = await messaging().getToken(); console.log(token); } awaits both calls and uses correct AuthorizationStatus check.

3. Final Answer:

   const authStatus = await messaging().requestPermission(); if (authStatus === messaging.AuthorizationStatus.AUTHORIZED) { const token = await messaging().getToken(); console.log(token); } -> Option A

4. Quick Check:

   Check permission first, then get token [OK]

Hint: Request permission first, then get token if authorized [OK]

Common Mistakes:

• Getting token before permission
• Not awaiting async calls
• Ignoring authorization status check