In recent times, Google moved from Google Cloud Messaging (GCM) to Firebase Cloud Messaging (FCM). Just like GCM, FCM is a cross-platform messaging solution that allows you to send messages. FCM is completely free and there are no limitations.

If you have followed any of my previous tutorials about GCM, I strongly recommend you migrate to Firebase today itself. In this article we learn the features of firebase cloud messaging by building a simple app. We’ll also learn how to integrate firebase to your backend, so that you can send the messages from your server.

1. Firebase Message types

Using Firebase Cloud Messaging you can send three types of messages i.e Notification Message, Data Message and message with both Notification & Data Payload.

1.1 Notification Message:

Notification messages are handled by firebase SDK itself. Typically the notification message contains title, message, icon etc., These message can be sent from firebase console UI. By sending this kind of messages, you won’t get much control over the notification. The notification will be shown automatically when the app is in background.

In order to send notification message, you need to use notification key in json data. An example of notification message is given below.

1.2 Data Message:

Data messages has to be handled by the android app. You can add this kind of messages if you want to send some additional data along with the notification. But sending these messages through firebase console is not possible. You need to have a server side logic to send the notification using Firebase API. You need to use data key when sending this message.

An example of data message json is given below.

1.3 Messages with both notification and data payload:

A message can also contains both notification and data payload. When these kind of messages are sent, it will be handled in two scenarios depending upon app state (background / foreground). For these message we can use both notification and data keys.

When in the background – Apps receive the notification payload in the notification tray, and only handle the data payload when the user taps on the notification.

When in the foreground – App receives a message object with both payloads available.

An example of notification & data payload message will be

2. Message Targeting

While sending message using firebase, you can choose the targeted audience. You can send either to a single user or to group of users using a topic name.

2.1 Sending to Single User

When a single user targeted, the firebase registration id is used to identify the device. The reg id has to be mentioned in to filed of json.

2.2 Topic Messaging

Topic messaging is useful when segment of users targeted for messaging. For this all the users has to subscribe to firebase topic. Ex: When you want to send message to all the users who are engaged with news, you can create a topic named news and send notification to news topic.

The request format of topic messaging is given below. In the to filed you need to mention the topic name.

3. Integrating Firebase Cloud Messaging

I hope the above information gave you good overview of firebase features and the options they are providing. Now we’ll create a simple app that receives firebase messages from both firebase console and from the PHP code.

1. First thing you need to do is go to https://firebase.google.com/ and make an account to gain access to their console. After you gain access to the console you can start by creating your first project.

2. Give the package name of your project (mine is info.androidhive.firebasenotifications) in which you are going to integrate the Firebase. Here the google-services.json file will be downloaded when you press add app button.

3. Create a new project in Android Studio from File ⇒ New Project. While filling the project details, use the same package name which you gave in firebase console. In my case I am using same info.androidhive.firebasenotifications.

4. Paste the google-services.json file to your project’s app folder. This step is very important as your project won’t build without this file.

5. Now open the build.gradle located in project’s home directory and add firebase dependency.

6. Open app/build.gradle and add firebase messaging dependency. At the very bottom of the file, add apply plugin: ‘com.google.gms.google-services’

7. Create three packages named activity, app, service and utils under your project folder. Below is the structure and files required for this project.

8. Download notification.mp3 and place it in res ⇒ raw folder. This step is optional, but if you want to play a custom notification sound when notification received.

9. Create a class named Config.java under app package. This class contains all the constant values that we use across the app.

10. Create a class named NotificationUtils.java under utils package. This class contains necessary functions required to show the message (with title, message, image and timestamp) in notification tray.

11. Create a class named MyFirebaseInstanceIDService.java under service package. This class receives the firebase registration id which will be unique to each app. This registration id is needed when you want to send message to a single device. You can send this token to your server app to send notification to devices later.

onTokenRefresh() method will be called whenever there is a change in firebase registration id.

storeRegIdInPref() stores the registration id in shared preferences.

LocalBroadcastManager – Broadcast manager broadcasts the reg id to all the activities those are listening.

12. Create another class named MyFirebaseMessagingService.java under service package. This class receives the firebase messages into onMessageReceived() method.

> When notification type message is sent, firebase automatically shows the notification when the app is in background. If the app is in foreground, handleNotification() method handles the notification message.

> When data type message is sent, handleDataMessage() method is used to handle the payload irrespective of app state (foreground / background).

> LocalBroadcastManager is used to broadcast the message to all the activities which are registered for the broadcast receiver.

13. Open AndroidManifest.xml and add the two firebase services MyFirebaseMessagingService and MyFirebaseInstanceIDService.

14. Finally we need to modify our main activity to display the incoming messages on the screen. Open layout file of main activity activity_main.xml and modify the layout as below.

15. Open MainActivity.java and do the below necessary changes. Here in onResume() method we are registering the broadcast receivers. So that this activity gets the push messages and registration id.

displayFirebaseRegId() fetches the firebase registration id from shared preferences and displays it on the screen. This is just for your references, we don’t use the reg id any where in the app.

Subscribing to Topic

When you want to subscribe to any topic, subscribeToTopic() function can be used. When a client app subscribes to a new topic name (one that does not already exist for your Firebase project), a new topic of that name is created in FCM and any client can subsequently subscribe to it.

Unsubscribing from Topic

Similarly the client can unsubscribe from a topic by calling unsubscribeFromTopic() method.

Now we have completed the integration of firebase cloud messaging. In order to verify it, run the project and you should see the firebase reg id on the screen. You can also find the reg id in LogCat.

4. Sending Messages from Firebase Console

Now we’ll send the first message from firebase console. Go to firebase console and click on Notifications in left menu. You will get an interface where you can type the message, select the targeting and send the message.

5. Sending Messages from PHP Backend

Sending message from firebase console is not always an optimal solution for lot of apps. Huge number of apps requires an automatic notification to user whenever there is an event, which is not possible using firebase console. To overcome this problem you need to integrate the firebase API from your backend server.

Let’s create a simple PHP project to send the messages from backend. I am assuming you are having basic knowledge of PHP and WAMP. If you are new you can get the help from this article.

5.1 Obtaining your Firebase Server API Key

Firebase provides Server API Key to identify your firebase app. To obtain your Server API Key, goto firebase console, select the project and goto settings, select Cloud Messaging tab and copy your Server key.

1. Goto your WAMP directory and create new folder named firebase inside htdocs or www.

2. Create a file named config.php and add the below code. Here we define the firebase Server API Key to send request to firebase endpoint.

3. Create a file named push.php This class prepares and the push notification json that needs to be send to firebase.

4. Create a file named firebase.php and add the below code. This class contains necessary functions to send message to firebase api by making a CURL request.

5. Finally create a index.php and add the below code. Here we are creating a simple UI which takes the input and send the notification to android device.

6. Access the project from your http://localhost/firebase url. (If your apache is running on a port, access the url using port number)

6. Demo

If you are new to PHP and facing any issue while running the above PHP project, you can access the same project here. The UI is same as explained above except few changes. You need to provide your own firebase Server API Key to test your app. Check the video to know how to use the demo page. Don’t worry about exposing your Server API Key, your data is not stored in any manner in the demo page.