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Firebase Android Codelab - Build Friendly Chat


Image: Working Friendly Chat app.

Welcome to the Friendly Chat codelab. In this codelab, you'll learn how to use the Firebase platform to create a chat app on Android.

What you'll learn

  • How to use Firebase Authentication to allow users to sign in.
  • How to sync data using the Firebase Realtime Database.
  • How to store binary files in Firebase Storage.

What you'll need

  • Android Studio version 4.0+.
  • An Android device or Emulator with Android 4.4+.
  • Familiarity with the Kotlin programming language.

Clone the repository

Clone the GitHub repository from the command line:

$ git clone

Import into Android Studio

In Android Studio click File > Open and select the build-android-start directory ( android_studio_folder) from the directory where you downloaded the sample code.

You should now have the build-android-start project open in Android Studio. If you see a warning about a google-services.json file missing, don't worry. It will be added in the next step.

Check Dependencies

In this codelab all of the dependencies you will need have already been added for you, but it's important to understand how to add the Firebase SDK to your app:


buildscript {
    // ...

    dependencies {
        classpath ''

        // The google-services plugin is required to parse the google-services.json file
        classpath ''
        classpath ''


plugins {
    id ''
    id 'kotlin-android'
    id ''

android {
    // ...

dependencies {
    // ...

    // Google Sign In SDK
    implementation ''

    // Firebase SDK
    implementation platform('')
    implementation ''
    implementation ''
    implementation ''

    // Firebase UI Library
    implementation 'com.firebaseui:firebase-ui-database:7.1.1'

// Apply the 'google-services' plugin
apply plugin: ''

In this step you will create a Firebase project to use during this codelab and add the project configuration to your app.

Create a new project

  1. In your browser go to the Firebase console.
  2. Select Add project.
  3. Select or enter a project name, you can use any name you want.
  4. You will not need Google Analytics for this project, so you can disable it when asked.
  5. Click Create Project and when your project is ready click Continue

Add Firebase to your app

Before you begin this step, get the SHA1 hash of your app: Run the command below in the project directory to determine the SHA1 of your debug key:

./gradlew signingReport

Store: /Users/<username>/.android/debug.keystore
Alias: AndroidDebugKey
MD5: A5:88:41:04:8F:06:59:6A:AE:33:76:87:AA:AD:19:23
SHA1: A7:89:F5:06:A8:07:A1:22:EC:90:6A:A6:EA:C3:D4:8B:3A:30:AB:18
SHA-256: 05:A2:2A:35:EE:F2:51:23:72:4D:72:67:A5:6A:8A:58:22:2C:00:A6:AB:F6:45:D5:A1:82:D8:90:A4:69:C8:FE
Valid until: Wednesday, August 10, 2044

You should see some output like the above, the important line is the SHA1 key. If you're unable to find your SHA1 hash see this page for more information.

Now in the Firebase console, follow these steps to add an Android app to your project:

  1. From the overview screen of your new project, click the Android icon to launch the setup workflow: add android app
  2. On the next screen, enter as the package name for your app.
  3. Click Register App and then click Download google-services.json to download the google-services configuration file.
  4. Copy the google-services.json file into the app directory in your project. After the file is downloaded you can Skip the next steps shown in the console (they've already been done for you in the build-android-start project).
  5. To be sure that all dependencies are available to your app, you should sync your project with gradle files at this point. Select File > Sync Project with Gradle Files from the Android Studio toolbar.

Now that you have imported the project into Android Studio and configured the google-services plugin with your JSON file, you are ready to run the app for the first time.

  1. Start your Android device or emulator.
  2. In Android Studio click Run ( execute) in the toolbar.

The app should launch on your device. At this point, you should see an empty message list, and sending and receiving messages will not work. In the next section, you authenticate users so they can use Friendly Chat.

This app will use Firebase Realtime Database to store all chat messages. Before we add data, we should make sure that the app is secure and that only authenticated users can post messages. In this step we will enable Firebase Authentication and configure Realtime Database Security Rules.

Configure Firebase Authentication

Before your application can access the Firebase Authentication APIs on behalf of your users, you will have to enable it

  1. Navigate to the Firebase console and select your project
  2. Select Authentication
  3. Select the Sign In Method tab
  4. Toggle the Google switch to enabled (blue)
  5. Set a support email.
  6. Press Save on the resulting dialog

If you get errors later in this codelab with the message "CONFIGURATION_NOT_FOUND", come back to this step and double check your work.

Configure Realtime Database

As mentioned, this app will store chat messages in Firebase Realtime Database. In this step we will create a database and configure the security via a JSON configuration language called Security Rules.

  1. Go to your project in the Firebase console and select Realtime Database from the left navigation.
  2. Click Create Database create a new Realtime Database instance and then select the us-central1 region and click Next.
  3. When prompted about security rules, choose locked mode and click Enable.

Once the database has been created, select the Rules tab and update the rules configuration with the following:

  "rules": {
    "messages": {
      ".read": "auth.uid != null",
      ".write": "auth.uid != null"

Click "Publish" to publish the new rules.

For more information on how this works (including documentation on the "auth" variable) see the Firebase security documentation.

Add basic sign-in functionality

Next we'll add some basic Firebase Authentication code to the app to detect users and implement a sign-in screen.

Check for current user

First add the following instance variable to the MainActivity.kt class:


// Firebase instance variables
private lateinit var auth: FirebaseAuth

Now let's modify MainActivity to send the user to the sign-in screen whenever they open the app and are unauthenticated. Add the following to the onCreate() method after the binding is attached to the view:


// Initialize Firebase Auth and check if the user is signed in
auth = Firebase.auth
if (auth.currentUser == null) {
    // Not signed in, launch the Sign In activity

We also want to check if the user is signed in during onStart():


public override fun onStart() {
    // Check if user is signed in.
    if (auth.currentUser == null) {
        // Not signed in, launch the Sign In activity

Then implement the getUserPhotoUrl() and getUserName() methods to return the appropriate information about the currently authenticated Firebase user:


private fun getPhotoUrl(): String? {
    val user = auth.currentUser
    return user?.photoUrl?.toString()

private fun getUserName(): String? {
    val user = auth.currentUser
    return if (user != null) {
    } else ANONYMOUS

Then implement the signOut() method to handle the sign out button:


private fun signOut() {

Now we have all of the logic in place to send the user to the sign-in screen when necessary. Next we need to implement the sign-in screen to properly authenticate users.

Implement the Sign-In screen

Open the file SignInActivity.kt. Here a simple Sign-In button is used to initiate authentication. In this step you will implement the logic to Sign-In with Google, and then use that Google account to authenticate with Firebase.

Add an Auth instance variable in the SignInActivity class under the // Firebase instance variables comment:


// Firebase instance variables
private lateinit var auth: FirebaseAuth

Then, edit the onCreate() method to initialize Firebase in the same way you did in MainActivity:


// Initialize FirebaseAuth
auth = Firebase.auth

Next, initiate signing in with Google. Update signIn() method to look like this:


private fun signIn() {
    val signInIntent = signInClient.signInIntent
    startActivityForResult(signInIntent, RC_SIGN_IN)

Next, implement the onActivityResult() method to handle the sign in result. If the result of the Google Sign-In was successful, use the account to authenticate with Firebase:


public override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
    super.onActivityResult(requestCode, resultCode, data)

    // Result returned from launching the Intent in signIn()
    if (requestCode == RC_SIGN_IN) {
        val task = GoogleSignIn.getSignedInAccountFromIntent(data)
        try {
            // Google Sign In was successful, authenticate with Firebase
            val account = task.getResult(
        } catch (e: ApiException) {
            // Google Sign In failed, update UI appropriately
            Log.w(TAG, "Google sign in failed", e)

Implement the firebaseAuthWithGoogle() method to authenticate with the signed in Google account:


private fun firebaseAuthWithGoogle(acct: GoogleSignInAccount?) {
    Log.d(TAG, "firebaseAuthWithGoogle:" + acct?.id)
    val credential = GoogleAuthProvider.getCredential(acct?.idToken, null)
        .addOnSuccessListener(this) {
            // If sign in succeeds the auth state listener will be notified and logic to
            // handle the signed in user can be handled in the listener.
            Log.d(TAG, "signInWithCredential:success")
        .addOnFailureListener(this) { e -> // If sign in fails, display a message to the user.
            Log.w(TAG, "signInWithCredential", e)
                this@SignInActivity, "Authentication failed.",

That's it! You've implemented authentication using Google as an Identity Provider in just a few method calls and without needing to manage any server-side configuration.

Test your work

Run the app on your device. You should be immediately sent to the sign-in screen. Tap the Google Sign-In button. You should then be sent to the messaging screen if everything worked well.

In this step we will add functionality to read and display messages stored in Realtime Database.

Import Sample Messages

  1. In the Firebase console, select Realtime Database from the left navigation menu.
  2. In the overflow menu of the Data tab, select Import JSON.
  3. Browse to the initial_messages.json file in the root of the cloned repository, and select it.
  4. Click Import.

Read Data

Synchronize messages

In this section we add code that synchronizes newly added messages to the app UI by:

  • Initializing the Firebase Realtime Database and adding a listener to handle changes made to the data.
  • Updating the RecyclerView adapter so new messages will be shown.
  • Adding the Database instance variables with your other Firebase instance variables in the MainActivity class:


// Firebase instance variables
// ...
private lateinit var db: FirebaseDatabase
private lateinit var adapter: FriendlyMessageAdapter

Modify your MainActivity's onCreate() method under the comment // Initialize Realtime Database and FirebaseRecyclerAdapter with the code defined below. This code adds all existing messages from Realtime Database and then listens for new child entries under the messages path in your Firebase Realtime Database. It adds a new element to the UI for each message:


// Initialize Realtime Database
db = Firebase.database
val messagesRef = db.reference.child(MESSAGES_CHILD)

// The FirebaseRecyclerAdapter class and options come from the FirebaseUI library
// See:
val options = FirebaseRecyclerOptions.Builder<FriendlyMessage>()
adapter = FriendlyMessageAdapter(options, getUserName())
binding.progressBar.visibility = ProgressBar.INVISIBLE
manager = LinearLayoutManager(this)
manager.stackFromEnd = true
binding.messageRecyclerView.layoutManager = manager
binding.messageRecyclerView.adapter = adapter

// Scroll down when a new message arrives
// See MyScrollToBottomObserver for details
    MyScrollToBottomObserver(binding.messageRecyclerView, adapter, manager)

Next in the FriendlyMessageAdapter.kt class implement the bind() method within the inner class MessageViewHolder():


inner class MessageViewHolder(private val binding: MessageBinding) : ViewHolder(binding.root) {
    fun bind(item: FriendlyMessage) {
        binding.messageTextView.text = item.text
        setTextColor(, binding.messageTextView)

        binding.messengerTextView.text = if ( == null) ANONYMOUS else
        if (item.photoUrl != null) {
            loadImageIntoView(binding.messengerImageView, item.photoUrl!!)
        } else {

We also need to display messages that are images, so also implement the bind() method within the inner class ImageMessageViewHolder():


inner class ImageMessageViewHolder(private val binding: ImageMessageBinding) :
    ViewHolder(binding.root) {
    fun bind(item: FriendlyMessage) {
        loadImageIntoView(binding.messageImageView, item.imageUrl!!)

        binding.messengerTextView.text = if ( == null) ANONYMOUS else
        if (item.photoUrl != null) {
            loadImageIntoView(binding.messengerImageView, item.photoUrl!!)
        } else {

Finally, back in MainActivity, start and stop listening for updates from Firebase Realtime Database. Update the onPause() and onResume() methods in MainActivity as shown below:


public override fun onPause() {

public override fun onResume() {

Test message sync

  1. Click Run ( execute).
  2. In the Firebase console return to the Realtime Database section and manually add a new message with the ID -ABCD. Confirm that the message shows up in your Android app:

Congratulations, you just added a realtime database to your app!

Implement text message sending

In this section, you will add the ability for app users to send text messages. The code snippet below listens for click events on the send button, creates a new FriendlyMessage object with the contents of the message field, and pushes the message to the database. The push() method adds an automatically generated ID to the pushed object's path. These IDs are sequential which ensures that the new messages will be added to the end of the list.

Update the click listener of the send button in the onCreate() method in the MainActivity class. This code is at the bottom of the onCreate() method already. Update the onClick() body to match the code below:


// Disable the send button when there's no text in the input field
// See MyButtonObserver for details

// When the send button is clicked, send a text message
binding.sendButton.setOnClickListener {
    val friendlyMessage = FriendlyMessage(
        null /* no image */

Implement image message sending

In this section, you will add the ability for app users to send image messages. Creating an image message is done with these steps:

  • Select image
  • Handle image selection
  • Write temporary image message to the Realtime Database
  • Begin to upload selected image
  • Update image message URL to that of the uploaded image, once upload is complete

Select Image

To add images this codelab uses Cloud Storage for Firebase. Cloud Storage is a good place to store the binary data of your app.

In the Firebase console select Storage in the left navigation panel. Then click Get Started to enable Cloud Storage for your project. Continue following the steps in the prompt, using the suggested defaults.

Handle image selection and write temp message

Once the user has selected an image, startActivityForResult() is called. This is already implemented in the code at the end of the onCreate() method. It launches the MainActivity's onActivityResult() method. Using the code snippet below, you will write a message with a temporary image url to the database indicating the image is being uploaded.


override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
    super.onActivityResult(requestCode, resultCode, data)
    Log.d(TAG, "onActivityResult: requestCode=$requestCode, resultCode=$resultCode")
    if (requestCode == REQUEST_IMAGE) {
        if (resultCode == RESULT_OK && data != null) {
            val uri =
            Log.d(TAG, "Uri: " + uri.toString())
            val user = auth.currentUser
            val tempMessage =
                FriendlyMessage(null, getUserName(), getPhotoUrl(), LOADING_IMAGE_URL)
                    DatabaseReference.CompletionListener { databaseError, databaseReference ->
                        if (databaseError != null) {
                                TAG, "Unable to write message to database.",

                                // Build a StorageReference and then upload the file
                                val key = databaseReference.key
                                val storageReference =
                                putImageInStorage(storageReference, uri, key)

Upload image and update message

Add the method putImageInStorage() to MainActivity. It is called in onActivityResult() to initiate the upload of the selected image. Once the upload is complete you will update the message to use the appropriate image.


private fun putImageInStorage(storageReference: StorageReference, uri: Uri, key: String?) {
    // First upload the image to Cloud Storage
        ) { taskSnapshot -> // After the image loads, get a public downloadUrl for the image
            // and add it to the message.
                .addOnSuccessListener { uri ->
                    val friendlyMessage =
                        FriendlyMessage(null, getUserName(), getPhotoUrl(), uri.toString())
        .addOnFailureListener(this) { e ->
                "Image upload task was unsuccessful.",

Test Sending Messages

  1. Click the executeRun button.
  2. Enter a message and hit the send button, the new message should be visible in the app UI and in the Firebase console.
  3. Tap the "+" image to select an image from your device. The new message should be visible first with a placeholder image, and then with the selected image once the image upload is complete. The new message should also be visible in the Firebase console, as an object in the Database and as a blob in Storage.

You just built a real-time chat application using Firebase!

What you learned

  • Firebase Authentication
  • Firebase Realtime Database
  • Cloud Storage for Firebase

Next try using what you learned to add Firebase to your own Android app! To learn more about Firebase visit