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Dimitar Stoyanov

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Push Notifications with Firebase Cloud Messaging

Dimitar Stoyanov

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  • Jan 17, 2018
  • 19 Min read
  • 13,135 Views
  • Jan 17, 2018
  • 19 Min read
  • 13,135 Views
Android

Introduction

This tutorial will get you familiar with the fundamentals of setting up push notifications in your Android project using Firebase.

Firebase serves as a module between your server and the devices that will be receiving the push notifications that you create. Your server informs Firebase that a notification has to be sent. Then Firebase does the work behind the scenes to get the notification published.

description

In order to establish connection with Firebase, you need to create a project for your own app in the Firebase console. You must set up your project in such a way that every time a user installs it, their device is registered in Firebase with a unique token. Although this may seem complex, the setup is actually simple.

Create a Firebase project

Head to the Firebase console, log in and create a new Android project. You will be asked to enter your package name. You can find your package name at the top of pretty much every Java file in your project. You can also find it in your AndroidManifest.xml file. (You can also add a SHA1 key for extra security measures, but that will not be required for this tutorial.)

Next, you will get a google-services.json file, which contains information about your project signature. In case you missed the instructions while creating your app, you need to add this file to your app directory, which you can find when you open your file structure to Project.

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After that you need to add the gms dependency in your project-level build.gradle file:

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buildscript {
dependencies {
// Add this line
 classpath 'com.google.gms:google-services:3.0.0'
    }
}

Then, add the corresponding plugin in your app-level build.gradle. You will also need to add a Firebase messaging dependency in this file.

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dependencies {
compile 'com.google.firebase:firebase-messaging:10.2.1'
}
// Bottom of your file
apply plugin: 'com.google.gms.google-services'

Note that the firebase-messaging dependency must be the same version as other gms libraries. Otherwise there is a strong chance that your app will fail to register the device and obtain a Firebase token. There is an even greater chance that the application won't compile at all because it fails to find the Firebase classes that you're about to implement.

Creating the Firebase Services

The next step is to create two services. One will handle the device registration process, and the other will handle receiving the actual notifications.

Go to your AndroidManifest.xml file and add these service declarations under the application tag:

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<service
		android:name=".notifications.MyFirebaseMessagingService"
		android:permission="com.google.android.c2dm.permission.SEND">
		<intent-filter>
			<action android:name="com.google.firebase.MESSAGING_EVENT" />
			<action android:name="com.google.android.c2dm.intent.RECEIVE" />
		</intent-filter>
	</service>
	<service android:name=".notifications.MyFirebaseInstanceIDService">
		<intent-filter>
			<action android:name="com.google.firebase.INSTANCE_ID_EVENT" />
		</intent-filter>
	</service>

Under the same tag you can also add metadata for default notification values, but it is not mandatory:

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<meta-data
		android:name="com.google.firebase.messaging.default_notification_icon"
		android:resource="@mipmap/ic_launcher" />
	<meta-data
		android:name="com.google.firebase.messaging.default_notification_color"
		android:resource="@color/colorTransparent" />
		<meta-data android:name="com.google.android.gms.version"
		android:value="@integer/google_play_services_version" />

The last thing that you need to add to your manifest file is a RECEIVE permission:

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<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />

Setting up the services

Next, go ahead and create those two Java class services that you declared in the manifest in a new package called notifications.

This is the implementation of the MyFirebaseInstanceIDService class:

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import android.content.SharedPreferences;
import android.preference.PreferenceManager;
import android.util.Log;
import com.google.firebase.iid.FirebaseInstanceId;
import com.google.firebase.iid.FirebaseInstanceIdService;
import co.centroida.notifications.Constants;
public class MyFirebaseInstanceIDService extends FirebaseInstanceIdService {
private static final String TAG = "MyFirebaseIIDService";

@Override
public void onTokenRefresh() {
	// Get updated InstanceID token.
	String refreshedToken = FirebaseInstanceId.getInstance().getToken();
	Log.d(TAG, "Refreshed token: " + refreshedToken);
	// If you want to send messages to this application instance or
	// manage this apps subscriptions on the server side, send the
	// Instance ID token to your app server.
	SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
	preferences.edit().putString(Constants.FIREBASE_TOKEN, refreshedToken).apply();
    }
}

The purpose of this service is very simple:

It obtains a Firebase Token, thereby forging the connection between the device and Firebase. Through this token, you can send notifications to this specific device. When obtained, this token is saved in a shared preference for future use. Naturally, you would like to send it to your server at some point, say user registration, or even right away, so that the server can send this device notifications through Firebase.

Moving on to the more interesting class, namely MyFirebaseMessagingService.

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public class MyFirebaseMessagingService extends FirebaseMessagingService {
@Override
public void onMessageReceived(RemoteMessage remoteMessage) {

   }
}

This service needs to extend FirebaseMessagingService. When the target device receives a notification, onMessageReceived is called. In your hands, you already have the remoteMessage object, which contains all the information that you received about the notification. Now let's create an actual notification with that information.

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@Override public void onMessageReceived(RemoteMessage remoteMessage) {

    notificationManager =
                (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

    //Setting up Notification channels for android O and above
    if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
        setupChannels();
    }
	int notificationId = new Random().nextInt(60000);

	Uri defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
	NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this, ADMIN_CHANNEL_ID)
			.setSmallIcon(R.drawable.ic_notification_small)  //a resource for your custom small icon
			.setContentTitle(remoteMessage.getData().get("title")) //the "title" value you sent in your notification
			.setContentText(remoteMessage.getData().get("message")) //ditto
			.setAutoCancel(true)  //dismisses the notification on click
			.setSound(defaultSoundUri);

	NotificationManager notificationManager =
			(NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

	notificationManager.notify(notificationId /* ID of notification */, notificationBuilder.build());

}

Here, to get unique notifications each time you receive a new message, for the sake of this example, we generate a random number and use it as notification ID. With this ID, you can do several things to your notifications. As such, you should probably group them if they are of the same kind, or update them. If you want to see each notification individually from the others, their IDs need to be different.

Android Oreo compatibility

Every app that targets SDK 26 or above (Android O) must implement notification channels and add its notifications to at least one of them. I won't go into the specifics of how those work, as it is out of the scope of this article. Simply put, you separate your notifications into channels based on their function and importance level. Having more channels gives the users more control over what notifications they receive. You can read more about channels here. If you want the newest phones to receive any of your notifications, paste this method in your service.

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    @RequiresApi(api = Build.VERSION_CODES.O)
    private void setupChannels(){
        CharSequence adminChannelName = getString(R.string.notifications_admin_channel_name);
        String adminChannelDescription = getString(R.string.notifications_admin_channel_description);

        NotificationChannel adminChannel;
        adminChannel = new NotificationChannel(ADMIN_CHANNEL_ID, adminChannelName, NotificationManager.IMPORTANCE_LOW);
        adminChannel.setDescription(adminChannelDescription);
        adminChannel.enableLights(true);
        adminChannel.setLightColor(Color.RED);
        adminChannel.enableVibration(true);
        if (notificationManager != null) {
            notificationManager.createNotificationChannel(adminChannel);
        }
    }

I've initialized a constant ADMIN_CHANNEL_ID which is of type String. I use that id variable to refer to my newly created channel. So every time I use NotificationCompat.Builder to create a new notification, I initialize the builder object and pass in the id in the constructor, like so:

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NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this, ADMIN_CHANNEL_ID) {...}

Background compatibility

Also another thing that should be noted is that we use remoteMessage.getData() to access the values of the received notification. Now, there are two types of Firebase notifications - data messages and notification messages.

Data messages are handled here in onMessageReceived whether the app is in the foreground or background. However, notification messages are received only when the app is in foreground, making them kind of useless or at least rather boring, don't you think?

For an unified notifications system, we use messages that have a data-only payload.

Messages containing both notification and data payloads are treated as notification messages, so they won't be handled by MyFirebaseMessagingService when the app is in the background!

If you haven't set up your server yet, you can still test your push notifications with a POST http request directly to Firebase. You can use any app you find fit for that, we use the Google Postman plugin. You can download it from this link.

The endpoint you can use from firebase is this one: https://fcm.googleapis.com/fcm/send

Obtaining the Server key:

This request requires an Authorization header, the value of which is the Server key of your application in Firebase, preceded by a key=. You can find it in your Project settings in the Firebase console under the tab Cloud messaging.

This is what your POST request should look like:

And this should be the body of your request:

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{
  "to":
    "d4_9RguWZNQ:APA91bH677zDilszjdf30-i12-0W-02314-0@0-123495-0-02-Something-rXEtW_wZNXa6K_-V96rEHPEysXSIfL",
  "data": {
    "title": "I'd tell you a chemistry joke",
    "message": "but I know I wouldn't get a reaction",
    "image-url":
      "https://docs.centroida.co/wp-content/uploads/2017/05/notification.png"
  }
}

In the body of your request you need to specify the "to" field to send a notification to the targeted device. It's value is the aforementioned Firebase token that your device obtains in MyFirebaseInstanceIDService. You can retrieve it from the log message or directly from the shared preferences. In the data payload, you can specify all kinds of key-value pairs that would suit your application needs.

Customizing notifications

Now that we can send and test notifications, we can make them fancier. First let's add a click functionality for the notification:

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    Intent notificationIntent;
    if(StartActivity.isAppRunning){
    		notificationIntent = new Intent(this, ChildActivity.class);
    	}else{
    		notificationIntent = new Intent(this, StartActivity.class);
    	}
	notificationIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

	final PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, notificationIntent,
			PendingIntent.FLAG_ONE_SHOT);

	...

	Uri defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
	NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this)
			.setSmallIcon(R.drawable.ic_notification_small)
			.setContentTitle(remoteMessage.getData().get("title"))
			.setContentText(remoteMessage.getData().get("message"))
			.setAutoCancel(true)
			.setSound(defaultSoundUri)
		    .setContentIntent(pendingIntent);

It is recommended that you handle users clicking the notification while the app is still running. In this case we use a static boolean isAppRunning to determine whether the root activity (StartActivity) is running.

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public class StartActivity extends AppCompatActivity {
public static boolean isAppRunning;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    	super.onCreate(savedInstanceState);
    	setContentView(R.layout.activity_start);
    }
    @Override
    protected void onDestroy() {
    	super.onDestroy();
    	isAppRunning = false;
    }
}

You should consider what you want your notification intent to do so that it handles both cases without breaking your app's navigation structure.

Adding an image

Pictures in notifications can be a great attention-grabber. This is how we can add an image to our push notification:

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Bitmap bitmap = getBitmapfromUrl(remoteMessage.getData().get("image-url")); //obtain the image
Uri defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
	NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this)
		    .setLargeIcon(bitmap)  //set it in the notification
			.setSmallIcon(R.mipmap.ic_launcher)
			.setContentTitle(remoteMessage.getData().get("title"))
			.setContentText(remoteMessage.getData().get("message"))
			.setAutoCancel(true)
			.setSound(defaultSoundUri)
			.setContentIntent(pendingIntent);
....
}
//Simple method for image downloading
public Bitmap getBitmapfromUrl(String imageUrl) {
try {
		URL url = new URL(imageUrl);
		HttpURLConnection connection = (HttpURLConnection) url.openConnection();
		connection.setDoInput(true);
		connection.connect();
		InputStream input = connection.getInputStream();
		return BitmapFactory.decodeStream(input);

	} catch (Exception e) {
		e.printStackTrace();
		return null;
	}
}

In this case we send an image URL in the notification payload for the app to download. Usually, such processes get executed on a separate thread. However, in this case, this class is a service, so once the code in onMessageReceived executes, the service, which is a thread different from the main thread, gets destroyed and with it goes every thread that was created by the service. Hence, we can afford to make the image download synchronously. This shouldn't pose a threat to performance, as the service thread is not the main thread.

Notification Styles

The NotificationCompat.Builder supports a few different types of styles for notifications, including a player and ones with custom layouts:

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Uri defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this)
			.setLargeIcon(bitmap)
			.setSmallIcon(R.drawable.ic_notification_small)
			.setContentTitle(remoteMessage.getData().get("title"))
		    .setStyle(new NotificationCompat.BigPictureStyle()
					.setSummaryText(remoteMessage.getData().get("message"))
					.bigPicture(bitmap))
			.setContentText(remoteMessage.getData().get("message"))
			.setAutoCancel(true)
			.setSound(defaultSoundUri)
			.setContentIntent(pendingIntent);

Notification buttons

You can also add buttons to your notifications:

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Intent likeIntent = new Intent(this,LikeService.class);
likeIntent.putExtra(NOTIFICATION_ID_EXTRA,notificationId);
	likeIntent.putExtra(IMAGE_URL_EXTRA,remoteMessage.getData().get("image-url"));
	PendingIntent likePendingIntent = PendingIntent.getService(this,notificationId+1,likeIntent,PendingIntent.FLAG_ONE_SHOT);

	Uri defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
	NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this)
			.setLargeIcon(bitmap)
			.setSmallIcon(R.mipmap.ic_launcher)
			.setContentTitle(remoteMessage.getData().get("title"))
			.setStyle(new NotificationCompat.BigPictureStyle()
					.setSummaryText(remoteMessage.getData().get("message"))
					.bigPicture(bitmap))
			.setContentText(remoteMessage.getData().get("message"))
			.setAutoCancel(true)
			.setSound(defaultSoundUri)
            .addAction(R.drawable.ic_favorite_true,
                       getString(R.string.notification_like_button),likePendingIntent) //Setting the action
			.setContentIntent(pendingIntent);

In this case we use an action that is unrelated to the app and regardless of whether the app is active or inactive a certain simple action is executed through another simple service that extends the Service class:

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public class LikeService extends Service {

    private static final String NOTIFICATION_ID_EXTRA = "notificationId";
    private static final String IMAGE_URL_EXTRA = "imageUrl";

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
    	//Saving action implementation
    	return null;
    }
}

The result of your efforts:

Summary

That's all you need to get started with push notifications in Android!

Here is the link to the github repo of the working example project from this tutorial: https://github.com/DimitarStoyanoff/Notifications

Now you can have some fun exploring and styling your notifications. I hope this tutorial helped you out and you found it enjoyable. Until next time!

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