Firebase Cloud Messaging is a real-time solution for sending notifications to client apps without any kind of charges. FCM can reliably transfer notifications of up to 4Kb of payload. In this article, a sample app showing how this service can be availed is developed. Though FCM also allows sending out notifications using an app server, here Firebase admin SDK is used. Follow the complete article to implement an example of FCM. 
Approach
Step 1: Add Firebase to the project and the required permissions To add firebase to the project please refer Adding Firebase to Android App. The following is the gist of adding FCM to the app. Go to Tools -> Firebase -> Cloud Messaging -> Set up Firebase Cloud Messaging
- Connect your app to Firebase: Complete the three steps of creating a Firebase project.
- Add FCM to the app.
Since receiving FCM notifications require the use of the internet, add the following permission to the AndroidManifest.xml file anywhere between the </application> and </manifest> tags.
<uses-permission android:name=”android.permission.INTERNET” />
Note: compile ‘…..’ this format for setting up dependencies is deprecated, instead, use implementation ‘…..’ to declare dependencies in case of any discrepancy.
Step 2: Add all the required drawable resources Here, the following icon has been used as a drawable resource. Add all the drawable resources to the drawable resource folder. 
Step 3: Customize the activity_main.xml Here, the home screen of the app just holds a TextView, however, one can customize the app as per the requirements.
activity_main.xml
Step 4: Create the Notification Layout Create a new notification.xml file to design the layout for the Notification. This step is stated as optional because the content and title too can be directly set too without customizing the appearance of the notification, however here the notification has the following layout. Here the Notification consists of:
- An ImageView
- A TextView for the Title
- A TextView for the Message.
notification.xml
Step 5: Create the message receiving class Create a FirebaseMessageReceiver.java class. This class extends the FirebaseMessagingService. Add the following code to the AndroidManifest.xml file between the </activity> and </application> tags to recognise the FirebaseMessagingService as a service in the app.
AndroidManifest.xml
Here the attribute ‘android: name’ is assigned the name of the Java file that extends the FirebaseMessagingService so pass the class name FirebaseMessageReceiver. This service is required to do any type of message handling beyond just receiving notifications, while the client app runs in the background. It also serves the purpose of receiving notifications in foreground apps and much more. The complete AndroidManifest.xml file is given below.
AndroidManifest.xml
Step 6: Working with FirebaseMessageReceiver.java (Java) or for Kotlin FirebaseMessageReceiver.kt. It overrides the onMessageReceived() method to handle 2 events:
- If Notification contains any data payload, i.e it is received from the app server.
- If Notification contains any notification payload, i.e. it is sent via the Firebase Admin SDK.
This method takes RemoteMessage as a parameter. RemoteMessage is a class that extends Object Class and implements Parcelable interface. It is nothing but the object of the message passed using FCM. The above method then calls a user-defined method showNotification() which in turn accepts two parameters. A detailed explanation is provided via comments in the code itself. A notification channel is required for Notifications in Android Versions greater than Oreo. In this example, since a customized notification is designed, a method getCustomDesign() is defined and called to set the resources accordingly. This method sets the custom layout for the display of the notification received. Assuming that only title and body are received from the notification, it appropriately maps the TextViews according to the IDs and sets the image resource for the notification. The complete code for this file is given below.
Java
package com.example.fcmnotfication_gfg;import android.app.NotificationChannel;import android.app.NotificationManager;import android.app.PendingIntent;import android.content.Context;import android.content.Intent;import android.os.Build;import android.widget.RemoteViews;import androidx.core.app.NotificationCompat;import com.google.firebase.messaging.FirebaseMessagingService;import com.google.firebase.messaging.RemoteMessage;public class FirebaseMessageReceiver extends FirebaseMessagingService { // Override onNewToken to get new token @Override public void onNewToken(@NonNull String token) { Log.d(TAG, "Refreshed token: " + token); } // Override onMessageReceived() method to extract the // title and // body from the message passed in FCM @Override public void onMessageReceived(RemoteMessage remoteMessage) { // First case when notifications are received via // data event // Here, 'title' and 'message' are the assumed names // of JSON // attributes. Since here we do not have any data // payload, This section is commented out. It is // here only for reference purposes. /*if(remoteMessage.getData().size()>0){ showNotification(remoteMessage.getData().get("title"), remoteMessage.getData().get("message")); }*/ // Second case when notification payload is // received. if (remoteMessage.getNotification() != null) { // Since the notification is received directly // from FCM, the title and the body can be // fetched directly as below. showNotification( remoteMessage.getNotification().getTitle(), remoteMessage.getNotification().getBody()); } } // Method to get the custom Design for the display of // notification. private RemoteViews getCustomDesign(String title, String message) { RemoteViews remoteViews = new RemoteViews( getApplicationContext().getPackageName(), R.layout.notification); remoteViews.setTextViewText(R.id.title, title); remoteViews.setTextViewText(R.id.message, message); remoteViews.setImageViewResource(R.id.icon, R.drawable.gfg); return remoteViews; } // Method to display the notifications public void showNotification(String title, String message) { // Pass the intent to switch to the MainActivity Intent intent = new Intent(this, MainActivity.class); // Assign channel ID String channel_id = "notification_channel"; // Here FLAG_ACTIVITY_CLEAR_TOP flag is set to clear // the activities present in the activity stack, // on the top of the Activity that is to be launched intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); // Pass the intent to PendingIntent to start the // next Activity PendingIntent pendingIntent = PendingIntent.getActivity( this, 0, intent, PendingIntent.FLAG_ONE_SHOT); // Create a Builder object using NotificationCompat // class. This will allow control over all the flags NotificationCompat.Builder builder = new NotificationCompat .Builder(getApplicationContext(), channel_id) .setSmallIcon(R.drawable.gfg) .setAutoCancel(true) .setVibrate(new long[] { 1000, 1000, 1000, 1000, 1000 }) .setOnlyAlertOnce(true) .setContentIntent(pendingIntent); // A customized design for the notification can be // set only for Android versions 4.1 and above. Thus // condition for the same is checked here. if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) { builder = builder.setContent( getCustomDesign(title, message)); } // If Android Version is lower than Jelly Beans, // customized layout cannot be used and thus the // layout is set as follows else { builder = builder.setContentTitle(title) .setContentText(message) .setSmallIcon(R.drawable.gfg); } // Create an object of NotificationManager class to // notify the // user of events that happen in the background. NotificationManager notificationManager = (NotificationManager)getSystemService( Context.NOTIFICATION_SERVICE); // Check if the Android Version is greater than Oreo if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) { NotificationChannel notificationChannel = new NotificationChannel( channel_id, "web_app", NotificationManager.IMPORTANCE_HIGH); notificationManager.createNotificationChannel( notificationChannel); } notificationManager.notify(0, builder.build()); }} |
Kotlin
package com.example.fcmnotfication_gfg;import android.app.NotificationChannelimport android.app.NotificationManagerimport android.app.PendingIntentimport android.content.Contextimport android.content.Intentimport android.os.Buildimport android.widget.RemoteViewsimport androidx.core.app.NotificationCompatimport androidx.core.content.ContextCompatimport androidx.test.core.app.ApplicationProviderimport com.google.firebase.messaging.FirebaseMessagingServiceimport com.google.firebase.messaging.RemoteMessageclass FirebaseMessageReceiver : FirebaseMessagingService() { // Override onNewToken to get new token override fun onNewToken(token: String) { super.onNewToken(token) } // Override onMessageReceived() method to extract the // title and // body from the message passed in FCM override fun onMessageReceived(remoteMessage: RemoteMessage) { // First case when notifications are received via // data event // Here, 'title' and 'message' are the assumed names // of JSON // attributes. Since here we do not have any data // payload, This section is commented out. It is // here only for reference purposes. /*if(remoteMessage.getData().size()>0){ showNotification(remoteMessage.getData().get("title"), remoteMessage.getData().get("message")); }*/ // Second case when notification payload is // received. if (remoteMessage.getNotification() != null) { // Since the notification is received directly from // FCM, the title and the body can be fetched // directly as below. showNotification( remoteMessage.getNotification().getTitle(), remoteMessage.getNotification().getBody() ) } } // Method to get the custom Design for the display of // notification. private fun getCustomDesign( title: String, message: String ): RemoteViews { val remoteViews = RemoteViews( ApplicationProvider.getApplicationContext<Context>().getPackageName(), R.layout.notification ) remoteViews.setTextViewText(R.id.title, title) remoteViews.setTextViewText(R.id.message, message) remoteViews.setImageViewResource( R.id.icon, R.drawable.gfg ) return remoteViews } // Method to display the notifications fun showNotification( title: String, message: String ) { // Pass the intent to switch to the MainActivity val intent = Intent(this, MainActivity::class.java) // Assign channel ID val channel_id = "notification_channel" // Here FLAG_ACTIVITY_CLEAR_TOP flag is set to clear // the activities present in the activity stack, // on the top of the Activity that is to be launched intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP) // Pass the intent to PendingIntent to start the // next Activity val pendingIntent = PendingIntent.getActivity( this, 0, intent, PendingIntent.FLAG_ONE_SHOT ) // Create a Builder object using NotificationCompat // class. This will allow control over all the flags var builder: NotificationCompat.Builder = NotificationCompat.Builder( ApplicationProvider.getApplicationContext<Context>(), channel_id ) .setSmallIcon(R.drawable.gfg) .setAutoCancel(true) .setVibrate( longArrayOf( 1000, 1000, 1000, 1000, 1000 ) ) .setOnlyAlertOnce(true) .setContentIntent(pendingIntent) // A customized design for the notification can be // set only for Android versions 4.1 and above. Thus // condition for the same is checked here. builder = builder.setContent( getCustomDesign(title, message) ) // Create an object of NotificationManager class to // notify the // user of events that happen in the background. val notificationManager = ContextCompat.getSystemService( Context.NOTIFICATION_SERVICE ) as NotificationManager? // Check if the Android Version is greater than Oreo if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O ) { val notificationChannel = NotificationChannel( channel_id, "web_app", NotificationManager.IMPORTANCE_HIGH ) notificationManager!!.createNotificationChannel( notificationChannel ) } notificationManager!!.notify(0, builder.build()) }} |
Now run the app on your emulator or in your mobile device. Step 8: Send the notification using FCM
- Go to Firebase console and choose the appropriate project.
- Choose Cloud Messaging.
- Choose Send your First Message. The following window pops up. Fill out the details. While the text field is compulsory, rest all is optional. One can also add an image using a link or upload it, however uploading an image cost additional storage charges.
- In the target section, choose the app domain.
- One can either send out the notification now or schedule it for some time in the future.
- Rest all the other fields are optional and can be left empty. Click on Review and then Publish.
