How can I send push notifications to specific users?

Prerequisites

Before diving into the matter, you must have the following:

• A smartphone application where you would like to integrate the push notification feature.
• Firebase account for setting up Firebase Cloud Messaging: an effective system that provides push notification functionality.
• Basic knowledge about different programming languages based on the platform (iOS or Android) you are developing your application.

Initiating Firebase Cloud Messaging

Step 1: Create a Project in Firebase Console

Firstly, you need to log in to your Google Firebase account and create a new project. Give it a name and associate it with a billing account (if you have any). You also need to accept Firebase's terms and conditions.

Step 2: Add Firebase to your Application

Upon creating the project successfully, you will get the option to add Firebase to your Android or iOS apps. Select the relevant one and you will be guided through the process.

For Android Applications: You need to provide your package name and SHA-1 key.

For iOS Applications: You need to provide your iOS bundle ID.

Step 3: Download Configuration File

You are then expected to download a configuration file that contains all the necessary Firebase connection parameters:

For Android Applications: Download the 'google-services.json' file.

For iOS Applications: Download the 'GoogleService-Info.plist' file.

For each platform, you need to move this file into your project directory.

Configure the Application to Receive Push Notifications

Step 1: Add Firebase SDK

Depending upon the language and platform of your application, add Firebase SDK to your project. It may vary as below:

For Android Applications: Add Firebase SDK by including the required dependencies in your build.gradle file.

For iOS Applications: You can add Firebase SDK using CocoaPods by placing necessary pods in your Podfile.

Step 2: Initialize Firebase SDK

For Android Applications: In your main Activity, generally 'MainActivity.java', initialize the Firebase App using FirebaseApp.initializeApp(context) function.

For iOS Applications: In your AppDelegate file ('AppDelegate.swift' for Swift or 'AppDelegate.m' for Objective C), initialize Firebase SDK using FirebaseApp.configure().

Step 3: Request User Permission for Notifications

In both Android and iOS applications, it's required to request the user's permission to send push notifications. You can use Firebase SDK's messaging model to request user permissions.

Sending Push Notifications to Specific Users

Step 1: Fetch and Store User's Unique FCM Token

Each application user gets a unique FCM token when they initialize Firebase. You can fetch this token and store it in your database. This token will be used to send notifications to this particular user. In your Firebase messaging service class, add the following code to fetch and print user's FCM token:

FirebaseMessaging.getInstance().getToken()
        .addOnCompleteListener(new OnCompleteListener<String>() {
    @Override
    public void onComplete(@NonNull Task<String> task) {
        if (!task.isSuccessful()) {
            Log.w(TAG, "Fetching FCM registration token failed", task.getException());
            return;
        }

        // Get new FCM registration token
        String token = task.getResult();

        // Log and toast
        String msg = getString(R.string.msg_token_fmt, token);
        Log.d(TAG, msg);
        Toast.makeText(MainActivity.this, msg, Toast.LENGTH_SHORT).show();
    }
});

Step 2: Use FCM Token to Send Notifications to a Specific User

Navigate to 'Cloud Messaging' from your Firebase Console. Click on 'Send your first message'. Fill in the necessary details for your notification including title, message text etc., and then click on 'Send Test Message'. Here, put in the FCM token you obtained earlier to send notifications to the user associated with that token.

And there you go! You have successfully sent a push notification to a specific user.