How to Retrieve and Save the FCM Device Token to the Realtime Firebase Storage?

To push notification to a particular device, the sender either needs the user’s device FCM token or the user should subscribe to a particular topic. One advantage of sending notifications via token, the server can send notifications to active users. To follow this practice, tokens need to be saved to the server or database. But the FCM device token follows some expiration policy. FCM token gets revoked on the following triggers:

1. Uninstall from a Particular device and install on a new device with the same credentials. 
2. User clears app data. 

We will examine obtaining the device FCM token and saving it to Firebase Realtime Database in this lesson. A sample video is given below to get an idea about what we are going to do in this article.

Step by Step Implementation

Step 1: 

To create a new project in Android Studio please refer to How to Create/Start a New Project in Android Studio. Note that select Kotlin as the programming language. Refer to this article to add Firebase to your Android App.

Step 2:

Click on tools under the menu bar section and click on Firebase and include Cloud Messaging dependencies into your build file.

Add Firebase Messaging Dependencies 

Step 3:

Add the below dependency to the app build file for firebase Real-time storage and sync the script.

implementation 'com.google.firebase:firebase-common-ktx:20.2.0'
implementation 'com.google.firebase:firebase-database:20.1.0'
implementation 'com.google.firebase:firebase-database-ktx:20.1.0'

Add rules to the Realtime Storage rules. Please read real-time storage rules documentation for the writing rules below implementation should not be implemented in production.

{
  "rules": {
    ".read": true,
    ".write": true
  }
}

Step 4:

Add the following line in Application Manifest File 

<uses-permission android:name="android.permission.INTERNET"/>

Step 5:

Navigate to the app > res > layout > activity_main.xml and add the below code to that file. Below is the code for the activity_main.xml file.

XML

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <ImageView
        android:id="@+id/imageView2"
        android:layout_width="185dp"
        android:layout_height="186dp"
        android:layout_marginTop="32dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@mipmap/ic_gfg_foreground" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="278dp"
        android:layout_height="169dp"
        android:layout_marginTop="44dp"
        android:gravity="center"
        android:text="Welcome"
        android:textColor="@color/green"
        android:textSize="50sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.496"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/imageView2" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="88dp"
        android:text="Obtain token and save"
        android:textAppearance="@style/TextAppearance.AppCompat.Large"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView"
        app:layout_constraintVertical_bias="0.0" />

</androidx.constraintlayout.widget.ConstraintLayout>

Step 6:

Refer to the code below to see how an FCM token can be retrieved and stored in the Firebase Realtime database. To understand the code, please note the comments. If the token expires, the code can be used. Below is the code for the MainActivity.kt file. Comments are added inside the code to understand the code in more detail.

Kotlin

package com.geeksforgeeks.fcmpost

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import android.widget.Toast
import com.google.android.gms.tasks.OnCompleteListener
import com.google.firebase.ktx.Firebase
import com.google.firebase.messaging.FirebaseMessaging
import com.google.firebase.database.ktx.database

class MainActivity : AppCompatActivity() {
    private lateinit var textview : TextView
    private lateinit var button : Button
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // textview reference
        textview = findViewById(R.id.textView)

        // button reference
        button = findViewById(R.id.button)

        // realtime database reference
        val realtimeDatabase = Firebase.database

        // button on click, firebase
        // token will obtain on clicking
        button.setOnClickListener {
            // Retrieving the FCM token
            FirebaseMessaging.getInstance().token.addOnCompleteListener(OnCompleteListener { task ->
                if (!task.isSuccessful) {
                    textview.text = "Fetching FCM registration token failed"
                    return@OnCompleteListener
                }

                // fetching the token
                val token = task.result

                textview.text = "Token saved successfully!"

                // directory reference
                val tokenDirRef = realtimeDatabase.getReference("Tokens")

                // storing the value
                tokenDirRef.setValue(token.toString())

                // toast to show  message
                Toast.makeText(
                    baseContext,
                    "Firebase Generated Successfully and saved to realtime database",
                    Toast.LENGTH_SHORT
                ).show()
            })
        }
    }
}

This is how the token will be saved in Realtime Firebase Database

Snippet from Realtime Firebase Database

Output: