How Push Notifications works internally at Web, Android & iOS?

Push notifications are messages sent by a server to a client application. These messages can be displayed even when the client application is not actively running.

Push notifications are called "push" notifications because the messages are "pushed" from the server to the client device, rather than the client device having to "pull" the information from the server. Here's a more detailed explanation:

Push vs. Pull Model

Push Model:

• In the push model, the server initiates the communication and sends (or "pushes") the notification to the client device as soon as new information is available.
• The client device doesn't need to make regular requests to the server to check for new information.
• This model is efficient for real-time updates and ensures that users receive notifications promptly.

Pull Model:

• In the pull model, the client device regularly initiates communication with the server to check (or "pull") for new information.
• The client must periodically make requests to the server to see if there are any updates.
• This model can be less efficient and may result in delays in receiving new information.

How Push Notifications Work

• Subscription: The client device (e.g., a smartphone, web browser) subscribes to receive notifications from a server.
• Notification Generation: When there is new information to share, the server generates a notification payload.
• Push Service: The server sends this payload to a push service (e.g., Firebase Cloud Messaging for Android, Apple Push Notification Service (FCM APNs Interface) for iOS). The push service acts as an intermediary, managing the connection to the client device.
• Delivery: The push service then pushes the notification to the client device. The client device receives the notification, even if the application is not actively running.

Benefits of Push Notifications

• Real-Time Updates: Push notifications provide real-time updates to users, ensuring they receive timely information.
• Efficiency: They reduce the need for the client device to repeatedly check for updates, saving bandwidth and battery life.
• User Engagement: Push notifications help keep users engaged by providing immediate alerts and updates.

Example

• Email Notifications: Instead of your email client constantly checking for new emails (pull), it waits for the email server to push notifications about new emails directly to your device.
• News Alerts: News apps push breaking news alerts to your device, ensuring you get the latest updates instantly without having to open the app and refresh for new content.

If a push notification is missed by the server or fails to reach the client device, the impact and subsequent actions depend on the underlying push notification service (e.g., FCM for Android, APNs for iOS) and the design of the application. Here's what generally happens and the mechanisms in place to handle such scenarios:

Factors Leading to Missed Notifications

• Server Issues:The server generating the push notification might experience downtime or errors.
• Network Issues:Network connectivity problems between the server and the push notification service can cause failures.
• Push Service Issues:Issues with the push notification service (e.g., FCM, APNs) might prevent the message from being delivered.
• Device Issues:The client device might be offline, have network issues, or have the app uninstalled or force-stopped.

Mechanisms to Handle Missed Notifications

Retry Mechanisms

• Server-Side Retries: The server can implement retry logic to attempt resending the notification if the initial send fails. Many push notification services provide feedback on message delivery status, allowing servers to retry failed attempts.
• Push Service Retries: Push notification services often have built-in retry mechanisms to handle transient network issues. For example, FCM and APNs may retry sending the notification for a limited period if the initial attempt fails.

Message Queueing and Storage

• Message Queueing: Some push notification services offer message queueing, where notifications are stored temporarily until the device is available. For instance, FCM can store messages for devices that are temporarily offline and deliver them when the device reconnects.
• TTL (Time-to-Live): Notifications can have a TTL setting, which specifies how long the message should be stored and retried before being discarded. This ensures that notifications remain relevant and are not delivered after becoming outdated.

User Experience Considerations

• In-App Syncing: Applications can implement in-app mechanisms to sync missed updates when the app is opened. For example, a messaging app can fetch missed messages from the server upon launch, ensuring no information is lost.
• Notification History: Some apps maintain a local history of notifications, allowing users to see past notifications even if some were missed.

Example Scenarios

• Server Outage: If the server is down and unable to send notifications, retries might be scheduled once the server is back online. The server might log such events and notify administrators to take corrective actions.
• Device Offline: If the device is offline, the push notification service (e.g., FCM) queues the message and delivers it when the device reconnects within the TTL period. If the TTL expires before the device comes online, the notification is discarded.
• Push Service Issues: If there are issues with the push notification service itself, it might retry delivery automatically. If persistent issues occur, monitoring systems might alert developers to investigate and resolve the underlying problem.

Here's a breakdown of how push notifications work on the Web, Android, and iOS, including the internal mechanisms:

Web Push Notifications:

1. User Subscription:

• A web application requests permission from the user to send notifications.
• If the user grants permission, the browser generates a unique subscription endpoint (a URL) and public/private key pair.

2. Service Worker:

• A Service Worker, a script that runs in the background, handles push notifications.
• The Service Worker intercepts network requests, caches resources, and manages notifications.

3. Push Service:

• Browsers use their own push services (e.g., Firebase Cloud Messaging for Chrome, Mozilla Push Service for Firefox).
• The subscription endpoint URL includes the push service endpoint, the unique client identifier, and keys for secure communication.

4. Sending a Notification:

• The web server stores the subscription details and sends a notification payload to the push service endpoint.
• The push service forwards the message to the respective browser, which then wakes up the Service Worker.
• The Service Worker receives the message and displays the notification using the Web Notifications API.

Android Push Notifications:

1. Firebase Cloud Messaging (FCM):

• FCM is the primary service for sending push notifications on Android.

2. App Registration:

• The app registers with FCM and receives a unique registration token.
• This token is sent to the server and used to identify the app instance.

3. Sending a Notification:

• The server sends a notification payload to FCM along with the registration token.
• FCM routes the message to the corresponding device.
• The Android system receives the message and delivers it to the app.
• If the app is in the background or closed, the notification is displayed in the system tray.
• If the app is in the foreground, the app handles the notification directly.

iOS Push Notifications

1. Apple Push Notification Service (APNs):

• APNs is the central service for sending push notifications on iOS devices.

2. App Registration:

• The app registers with APNs and receives a unique device token.
• The device token is sent to the server and used to identify the device.

3. Sending a Notification:

• The server sends a notification payload to APNs along with the device token.
• APNs routes the message to the corresponding device.
• The iOS system receives the message and delivers it to the app.
• If the app is in the background or closed, the notification is displayed on the lock screen or notification center.
• If the app is in the foreground, the app handles the notification directly.

When an app is in the background or closed, push notifications are handled differently by each operating system (Android and iOS). Here’s a detailed look at how it works internally for both platforms:

Android

1. Push Notification Reception

• Firebase Cloud Messaging (FCM): When a notification is sent from the server, FCM handles the delivery of the message to the device. This happens via a persistent connection between the device and FCM servers.

2. System-Level Handling

• System Tray: If the app is in the background or closed, the notification is intercepted by the Android system. The system then displays the notification in the system tray. The NotificationManager class is responsible for handling notifications at the system level.

3. Notification Display

• NotificationManager: The NotificationManager retrieves the notification payload and displays it in the system tray. This includes setting up notification content like the title, text, icon, and other optional features such as action buttons.

4. User Interaction

• Notification Taps: When a user taps on the notification, the system launches the app or brings it to the foreground, passing any relevant data (intent) that was included in the notification payload. The app can then handle this intent to perform specific actions or display certain content to the user.

public class MyFirebaseMessagingService extends FirebaseMessagingService {

    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
        // Handle FCM messages here.
        // If the message contains a data payload, process it.
        if (remoteMessage.getData().size > 0) {
            // Handle message data
        }

        // If the message contains a notification payload, display it.
        if (remoteMessage.getNotification() != null) {
            sendNotification(remoteMessage.getNotification().getBody());
        }
    }

    private void sendNotification(String messageBody) {
        Intent intent = new Intent(this, MainActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_ONE_SHOT);

        NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this, "channel_id")
                .setSmallIcon(R.drawable.ic_notification)
                .setContentTitle("My Notification")
                .setContentText(messageBody)
                .setAutoCancel(true)
                .setContentIntent(pendingIntent);

        NotificationManager notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        notificationManager.notify(0, notificationBuilder.build());
    }
}        

iOS

1. Push Notification Reception

• Apple Push Notification Service (APNs): When a notification is sent from the server, APNs handles the delivery of the message to the device.

2. System-Level Handling

• Notification Center: If the app is in the background or closed, iOS handles the notification and displays it in the Notification Center or on the lock screen. iOS takes care of this using its internal notification handling mechanisms.

3. Notification Display

• UNNotification Framework: The User Notifications framework (UserNotifications.framework) is used to manage and display notifications. This framework allows developers to customize the content and appearance of notifications.

4. User Interaction

• Notification Taps: When a user taps on the notification, the system launches the app or brings it to the foreground, passing the notification payload to the app. The app receives this payload via the application(_:didReceiveRemoteNotification:fetchCompletionHandler:) method or similar delegate methods, allowing the app to handle the notification data and perform specific actions.

import UserNotifications

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterDelegate {

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        UNUserNotificationCenter.current().delegate = self
        // Request notification permissions
        UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound, .badge]) { granted, error in
            // Handle permission granted/denied
        }
        application.registerForRemoteNotifications()
        return true
    }

    func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable: Any], fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
        // Handle remote notification
        if let aps = userInfo["aps"] as? [String: AnyObject] {
            handleNotification(aps: aps)
        }
        completionHandler(.newData)
    }

    private func handleNotification(aps: [String: AnyObject]) {
        // Process notification payload
        if let alert = aps["alert"] as? String {
            // Display alert
        }
    }

    // Handle notification when app is in the foreground
    func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
        completionHandler([.alert, .sound])
    }
}        

We can use batch processing and distributed processing to deliver notifications to millions of devices.

For a comprehensive guide on sending notifications from the backend using Kafka, SNS, and SQS, check out the following article:

https://www.dhirubhai.net/feed/update/urn:li:activity:7222178814204768256/

Steps to View Push Notification Connections in Chrome Network Tab

1. Open Chrome Developer Tools
2. Go to the Network Tab
3. Filter by Push Connections: Push notifications use the HTTP/2 protocol and are typically visible under the "WS" (WebSocket) or "Other" filter. In the Network tab, apply the "Other" filter to see connections related to push notifications.
4. Initiate a Push Notification: If you are testing a web application that uses push notifications, trigger the push notification. This can be done by sending a notification from your server or simulating one through the application.
5. Identify Push Notification Requests: Look for network requests labeled as push or showing the endpoint for your push service (e.g., URLs starting with https://fcm.googleapis.com for Firebase Cloud Messaging).These requests will show up in the list of network activities. Click on these requests to view detailed information.
6. Inspect Request and Response Details: Click on the relevant network request to open the detailed view. In the detailed view, you can see headers, payload data, and other relevant information about the request and response.

Here's how to test at the Application storage:

https://help.batch.com/en/articles/1617389-how-can-i-send-a-test-notification-to-my-web-browser

Firebase Cloud Messaging (FCM) does not use WebSockets for push notifications. Instead, it relies on a different set of technologies to deliver messages to devices:

1. HTTP/2: For sending messages from your server to FCM, the FCM API uses HTTP/2. This protocol allows for efficient and reliable communication between your server and FCM.
2. XMPP (Extensible Messaging and Presence Protocol): For real-time messaging and handling notifications in certain use cases, FCM uses XMPP. This protocol is designed for real-time messaging and can maintain a persistent connection with the server.
3. Google's Internal Infrastructure: For delivering messages from FCM to client devices, Google uses its internal infrastructure. This involves various mechanisms to ensure messages are delivered reliably and efficiently.

So, while WebSockets are a popular choice for real-time communication in some scenarios, FCM uses a combination of HTTP/2 and XMPP to handle push notifications and message delivery.

Amazon SNS (Simple Notification Service) and Amazon SQS (Simple Queue Service) do not use WebSockets for push notifications or messaging. Here's how each service typically operates:

Amazon SNS (Simple Notification Service):

• Push Notifications: SNS supports push notifications to various endpoints, such as mobile devices, email, SMS, and HTTP/S endpoints. For HTTP/S endpoints, SNS uses HTTP or HTTPS requests to deliver messages. It does not use WebSockets for this purpose.
• Pub/Sub Model: SNS uses a publish/subscribe model, where messages are sent to topics and then distributed to all subscribers of that topic. The distribution mechanism is based on protocols like HTTP/S, email, SMS, or application-specific protocols.

Amazon SQS (Simple Queue Service):

• Message Queuing: SQS is a message queuing service that allows for decoupling of microservices and distributed systems. It uses standard HTTP/HTTPS protocols to send and receive messages from queues.
• Polling: Clients can poll SQS queues to retrieve messages, but SQS itself does not use WebSockets. Polling can be done using long polling to reduce the number of empty responses and improve efficiency.

Hence, both SNS and SQS rely on standard HTTP/HTTPS protocols rather than WebSockets for their communication and messaging operations.

Example at React Native and React Web using Firebase Cloud Messaging and Push.js (Web):

React Native (Android & iOS):

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

import logger from './log';
import Storage from './storage';
import { getUniqueDeviceId } from './device';
import { successNotification } from './notifications';
import { db, FieldValue, auth } from './firebase';

import { Collections } from 'constants/Firestore';
import StorageKeys from 'constants/Storage';

async function storeFCMToken(token) {
  const uid = auth.currentUser?.uid;
  if (!(uid && token)) return;
  const deviceId = getUniqueDeviceId();
  let dbToken = null;
  try {
    dbToken = await Storage.load({ key: StorageKeys.fcmToken });
  } catch (e) {}

  if (dbToken !== token) {
    Storage.save({ key: StorageKeys.fcmToken, data: token });
    await db
      .collection(Collections.users)
      .doc(uid)
      .collection(Collections.private)
      .doc('private')
      .update({
        [`fcmTokens.${deviceId}`]: token,
      });
  }
}

export async function removeFCMToken() {
  const uid = auth.currentUser?.uid;
  await messaging().deleteToken(); // TODO: test this
  if (!uid) return;
  const deviceId = getUniqueDeviceId();
  Storage.remove({ key: StorageKeys.fcmToken });
  await db
    .collection(Collections.users)
    .doc(uid)
    .collection(Collections.private)
    .doc('private')
    .update({
      [`fcmTokens.${deviceId}`]: FieldValue.delete(),
    });
}

// Only for iOS. On Android it will always revolve successfully
export async function initMessaging() {
  const authStatus = await messaging().requestPermission();
  const enabled =
    authStatus === messaging.AuthorizationStatus.AUTHORIZED || authStatus === messaging.AuthorizationStatus.PROVISIONAL;

  if (enabled) {
    try {
      const fcmToken = await messaging().getToken();
      await storeFCMToken(fcmToken);
    } catch (e) {
      logger('FCM::INIT_MESSAGING ', e);
    }
  }
}

export function onTokenRefresh() {
  return messaging().onTokenRefresh(async token => storeFCMToken(token));
}

export function onMessage() {
  return messaging().onMessage(async remoteMessage => {
    const { title, body } = remoteMessage.notification;
    successNotification(title, body, 6000);
  });
}        

useEffect(() => {
    const unsubscribeOnTokenRefresh = onTokenRefresh();
    const unsubscribeOnMessage = onMessage();
    return function cleanup() {
      unsubscribeOnTokenRefresh?.();
      unsubscribeOnMessage?.();
    };
}, []);        

export async function initUser(uid) {
  const publicUserSnap = await db.collection(Collections.users).doc(uid).get();
  const privateUserSnap = await db
    .collection(Collections.users)
    .doc(uid)
    .collection(Collections.private)
    .doc('private')
    .get();

  const userData = {
    ...publicUserSnap.data(),
    ...privateUserSnap.data(),
    id: uid,
  };

  return userData;
}

useEffect(() => {
    const uid = getCurrentUserId();
    if (uid) {
      const user = await initUser(uid);
      await updateUser(user);
      initMessaging().catch(e => logger('INITIALIZE_MESSAGING', e));
    }
}, []);        

React Web:

import { isSupported, getToken, onMessage, getMessaging } from 'firebase/messaging';
import Push from 'push.js';

import { storeFCMToken } from './token';

import Config from 'config/config.json';
import { getNotificationPermission } from 'utils/notifications';

export async function initMessaging() {
  let unsubsOnMessage;
  if ((await isSupported()) && (await getNotificationPermission())) {
    const messaging = getMessaging();
    const token = await getToken(messaging, { vapidKey: Config.firebase.vapidKey });
    await storeFCMToken(token);
    unsubsOnMessage = onMessage(messaging, (payload) => {
      const { title, body } = payload.notification;
      Push.create(title, {
        body,
        icon: '../assets/images/header/logo.png',
        onClick() {
          window.focus();
          this.close();
        },
      });
    });
  }
  return unsubsOnMessage;
}        

import { deleteField } from 'firebase/firestore';
import { nanoid } from 'nanoid';

import { updateUserDocument, updateUserPrivateDocument } from './users';

import { Storage } from 'constants/index';
import { auth } from 'utils/firebase';

export async function removeFCMToken() {
  const uid = auth?.currentUser?.uid;
  if (!uid) return;
  const deviceId = localStorage.getItem(Storage.deviceId);
  localStorage.removeItem(Storage.token);
  await deleteToken(uid, deviceId);
}

export const deleteToken = async (uid, deviceId) => {
  await updateUserDocument(uid, { [`tokens.${deviceId}`]: deleteField() });
};

export async function storeFCMToken(token) {
  const uid = auth?.currentUser?.uid;
  if (!(uid && token)) return;
  let deviceId = localStorage.getItem(Storage.deviceId);
  if (!deviceId) {
    deviceId = nanoid();
    localStorage.setItem(Storage.deviceId, deviceId);
  }
  const dbToken = localStorage.getItem(Storage.token);
  if (dbToken !== token) {
    localStorage.setItem(Storage.token, token);
    await addToken(uid, deviceId, token);
  }
}

export const addToken = async (uid, deviceId, token) => {
  await updateUserPrivateDocument(uid, { [`fcmTokens.${deviceId}`]: token });
};        

  const onLogout = async () => {
    await removeFCMToken();
    await signOut(auth);
    updateUser(null);
    clearFreshChatUser();
    history.replace('home');
  };        

<ProfileButton onLogin={onLogin} onLogout={onLogout} />        

  useEffect(() => {
    let unsubsInitMessage;
    const unsubscribe = onAuthStateChanged(auth, async (user) => {
      if (user) {
        const userData = await getCurrentUser();
        unsubsInitMessage = await initMessaging();
        updateUser(userData);
        setFreshChatUser(userData);
        if (!userData.userName || !userData.displayName) {
          setStep(1);
          setLoginModalVisibility(true);
        }
      } else updateUser(null);
    });

    return function cleanup() {
      if (unsubscribe) unsubscribe();
      if (unsubsInitMessage) unsubsInitMessage();
    };
  }, []);        

Node.js Backend (Firebase Cloud Messaging):

import * as admin from 'firebase-admin';
import * as functions from 'firebase-functions';
import { PubSub } from '@google-cloud/pubsub';

admin.initializeApp();
const pubSubClient = new PubSub();

export const db = admin.firestore();
export const adminAuth = admin.auth();
export const config = functions.config();
export const bucket = admin.storage().bucket();
export const messaging = admin.messaging();

const functionsInRegion = functions.region('europe-west1');
export const { onCall, onRequest } = functionsInRegion.https;
export const firestoreTrigger = functionsInRegion.firestore;
export const authTrigger = functionsInRegion.auth.user();
export const { firestore } = admin;
export const { HttpsError } = functions.https;
export const { logger } = functions;
export const { pubsub } = functionsInRegion;

export function runWithOnRequest(options, fn) {
  return functionsInRegion.runWith(options).https.onRequest(fn);
}

export async function sendNotifications(tokens, notification = {}, data = {}) {
  try {
    await messaging.sendToDevice(tokens, { data, notification }, { contentAvailable: true, priority: 'high' });
  } catch (e) {
    logger.log('Sending notification failed', e);
    console.error(e);
  }
}

export async function publishNotiEvent(lsId) {
  await pubSubClient.topic('notifyUsers').publish(Buffer.from(JSON.stringify({ lsId })));
}        

import { Collections } from 'constants';

import { db, firestore, sendNotifications } from 'utils/firebase';

export default async function notifyUsers(data /* , context */) {
  const { lsId } = data.json;

  const livestreamDocRef = db.collection(Collections.liveStreams).doc(lsId);
  const tokens = [];

  const lsData = (await livestreamDocRef.get()).data();
  const { subscribedUsers, userId, title } = lsData;
  const batch = db.batch();

  if (!subscribedUsers) return;
  for (const subscribedUser of subscribedUsers) {
    const userDocRef = db
      .collection(Collections.users)
      .doc(subscribedUser)
      .collection(Collections.private)
      .doc('private');
    const docData = (await userDocRef.get()).data();
    if (docData?.fcmTokens) tokens.push(...Object.values(docData.fcmTokens));
    batch.update(userDocRef, { subscribedLiveStreams: firestore.FieldValue.arrayRemove(lsId) });
  }

  batch.update(livestreamDocRef, { subscribedUsers: firestore.FieldValue.delete() });
  await batch.commit();

  const userData = (
    await db
      .collection(Collections.users)
      .doc(userId)
      .get()
  ).data();

  const notiConfig = { title: `${title} will start soon`, body: `${userData.displayName} will start the livestream` };
  await sendNotifications(tokens, notiConfig);
}        

async function movePrivateUserData() {
  const { docs } = await db.collection('users').get();
  let i = 0;

  const batch = db.batch();
  for (const user of docs) {
    const { id } = user;
    console.log(id);

    const data = user.data();

    const { displayName, photoURL, userName = `user${i++}`, bio = '', author = false, tokens, ...privateData } = data;
    const publicData = { displayName, photoURL, userName, bio, author };
    privateData.fcmTokens = tokens ?? [];

    const privateRef = db
      .collection('users')
      .doc(id)
      .collection('private')
      .doc('private');

    batch.set(user.ref, publicData);
    batch.set(privateRef, privateData, { merge: true });
  }

  await batch.commit();
  return 'success';
}        

If a server delivers a message to Firebase Cloud Messaging (FCM) but the Android device misses it, several scenarios and mechanisms can come into play to handle such situations:

Potential Reasons for Missing Messages

1. Network Issues: The device might have been offline or had a poor network connection at the time of delivery.
2. Device Sleep: The device may have been in deep sleep mode, which can delay or prevent message delivery.
3. App Not Running: If the app was not running or was in the background, it might not have been able to process the message in real-time.
4. Token Expiry: The FCM registration token might have expired or been invalidated.

Mechanisms to Handle Missing Messages

1. Message Persistence: FCM's Built-In Mechanism: FCM provides built-in message persistence. FCM attempts to deliver messages to devices for a period of time (usually up to four weeks) even if the device is temporarily offline or unavailable. Messages are stored on FCM servers until the device comes back online.
2. Message Priority: High Priority: For important messages that must be delivered immediately, you can set the message priority to "high" in FCM. High-priority messages are more likely to be delivered promptly, even if the device is in doze mode. Normal Priority: For less time-sensitive messages, you can use "normal" priority, which will be delivered when the device is awake or actively using the app.
3. Retry Logic: Implement retry logic in your app to handle cases where messages are missed. The app can reattempt to fetch any missed data or notifications when it starts up or when it reconnects to the network.
4. Local Storage and Sync: Use local storage or caching mechanisms to store notifications or messages temporarily. When the device reconnects or the app is reopened, it can sync with the server to retrieve any missed messages.
5. Notification Channels: Use custom notification channels to manage different types of notifications. This can help prioritize important notifications and ensure that they are handled appropriately.
6. Token Management: Ensure your app correctly handles token refreshes and updates. This avoids issues with expired or invalid tokens that could result in missed messages.

Best Practices

• Handle Offline Scenarios: Implement logic in your app to handle offline scenarios gracefully, such as showing a notification when the app is back online or allowing users to manually sync data.
• Monitor Delivery: Use analytics and monitoring tools to track message delivery rates and identify any potential issues with message delivery or token management.

By employing these strategies, you can mitigate the impact of missed messages and ensure a more reliable push notification experience for users.

If an Android device receives a push notification but the notification is missed or not acted upon, there are several factors and potential solutions to consider:

Potential Reasons for Missed Notifications:

1. App in Background or Closed:

- Background Processing: If the app is in the background or closed, the notification may not be immediately visible or actionable. The notification might get dismissed or overlooked by the user.

2. Notification Overwrites:

- Notification Overwriting: If multiple notifications are sent, newer ones might overwrite older ones if they share the same notification ID. This can cause earlier notifications to be missed.

3. User Actions:

- Accidental Dismissal: Users might accidentally swipe away or dismiss notifications before viewing them.

4. Device Settings:

- Notification Settings: Device settings or app-specific notification settings might be configured to limit the visibility or importance of notifications.

5. Notification Channels:

- Channel Configuration: Notifications sent to a particular channel might not be configured to show prominently, or the user might have disabled notifications for that channel.

Mechanisms to Address Missed Notifications

1. Notification Management:

- Persistent Notifications: Use persistent notifications to ensure important messages remain visible until the user interacts with them. Set appropriate priority levels to make notifications more noticeable.

- Custom Actions: Include actionable buttons in your notifications to encourage users to interact with them.

2. In-App Notifications:

- In-App Messaging: Implement in-app notifications or messages within the app to inform users of missed updates or actions required. This can be useful if the user opens the app later.

3. Local Storage and Sync:

- Message Caching: Cache important messages or updates locally within the app. When the user opens the app, they can see any missed information or notifications.

- Sync Mechanisms: Use data sync mechanisms to fetch missed notifications or updates from the server when the app starts or when the user reconnects to the internet.

4. Notification Channels:

- Channel Configuration: Ensure that notification channels are configured properly, allowing users to customize their notification preferences. Provide clear and actionable notification settings to enhance user engagement.

5. Analytics and Monitoring:

- Track Delivery: Implement analytics to track notification delivery and interaction rates. This helps identify patterns of missed notifications and improves future notification strategies. Best Practices

- Provide Clear Context: Ensure notifications provide enough context and actionable content so users understand the importance and can act upon them quickly.

- User Preferences: Respect user preferences and settings regarding notifications. Provide settings within the app for users to customize their notification experience.

- Engagement Strategies: Consider using additional engagement strategies such as in-app messages, reminders, or follow-up notifications to address missed or ignored notifications.

By incorporating these practices, you can improve the effectiveness of push notifications and minimize the impact of missed notifications on user experience.

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