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How to Build an Android Chat Application in Kotlin

· 2 min read
Beniamin Marcu
Full Stack Developer

In this step-by-step tutorial we'll build a real-time Android chat application in Kotlin. This guide reuses the full source code from our premium Android Chat App.

How to Build an Android Chat Application in Kotlin​

android chat application tutorial

To build a fully-fledged Android chat application you should include these core features:

  • Real-time Messaging
  • Photo Messaging
  • Private Messaging
  • Group Chatting
  • Push Notifications
  • Messages Archive
  • Online Status

We leverage Firebase as the backend. More specifically we use:

  • Firebase Auth — user management (Login, Registration, Facebook Login, Google Login, etc.)
  • Firebase Firestore — real-time database for users and messages
  • Firebase Storage — stores photos and videos sent from the app
  • Firebase Cloud Messaging — sends real-time push notifications to message recipients

High-level steps to get started:

  1. Open & Run the Kotlin project in Android Studio
  2. Override google-services.json with your own file (downloaded from Firebase Console). This will wire the chat application to your Firebase project. Enable Firebase Auth providers and Firebase Storage; for Firestore, set read/write rules appropriately during development.
  3. Publish the app to Google Play Store

It looks straightforward — we'll walk through these milestones and also cover enabling push notifications.

Enable Push Notifications​

To send real-time push notifications you need the correct Server Key from Firebase Console.

Go to Firebase Console → Your Project → Project Settings → Cloud Messaging and copy the Server Key (Authorization key). It looks like this:

AAAAeliTfEs:APA91bGve5fyExjSiUCB0oI09Br1yGUSb0tPHelAk7L0FUytHWGOMlBPexJubTwSjjJTaIlK7oto3jDevoj9c5Q4Qalk6QEtQ9Y3tYfTxHD7OrmPZuVJjVGGciPBJXThG9QHCZQqx9Id

In Android Studio open AppConstants.kt (usually under the Utils folder) and replace the SERVER_KEY field with your authorization token.

Re-run the project and send some messages to verify push notifications are delivered.

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