Kotlin Chat Messaging Tutorial

How to Build In-App Messaging with Kotlin or Java.

Creating a Project

Already all-in on Jetpack Compose? Check out our Compose tutorial instead of this one!

The completed app for each step of the tutorial is available on GitHub.

To get started with the Android Chat SDK, open Android Studio and create a new project.

  • Select the Empty Views Activity template
  • Name the project ChatTutorial
  • Set the package name to com.example.chattutorial
  • Select your language - Kotlin (recommended) or Java
  • Set the Minimum SDK to 21 (or higher)
  • JVM targets 11 (or higher)

Set up demo messaging app in Android Studio

Make sure you're using a Material theme in your app

If you're using an up-to-date version of Android Studio, your newly created project should already be using a Theme.MaterialComponents theme as the parent to its app theme (you can check this in styles.xml or themes.xml). If you're running an older version, change the parent theme to be a Material theme instead of Theme.AppCompat.

If you want to keep using AppCompat theming, you can use a Bridge Theme instead.

Our SDKs are available from MavenCentral, with some of our dependencies being hosted on Jitpack. Update your repositories in the settings.gradle file like so:

First, we'll enable View Binding. Next, we're going to add the Stream Chat SDK and Coil to our project dependencies. Open up the app module's build.gradle script and make the following changes:

After you edit your Gradle files, make sure to sync the project (Android Studio will prompt you for this) with the new changes.

Displaying a List of Channels

Stream provides a low-level client, an offline support library, and convenient UI components to help you quickly build your messaging interface. In this section, we'll be using the UI components to quickly display a channel list.

First, open up activity_main.xml, and change the contents of the file to the following to display a full screen ChannelListView:

Next, open up MainActivity and replace the file's contents with the following code:

Let's have a quick look at the source code shown above:

  • Step 1: We create a StreamOfflinePluginFactory to provide offline support. The OfflinePlugin class employs a new caching mechanism powered by side-effects we applied to ChatClient functions.
  • Step 2: We create a connection to Stream by initializing the ChatClient using an API key. This key points to a tutorial environment, but you can sign up for a free Chat trial to get your own later. Next, we add the offlinePluginFactory to the ChatClient with withPlugin method for providing offline storage capabilities. For a production app, we recommend initializing this ChatClient in your Application class.
  • Step 3: We create a User instance and pass it to the ChatClient's connectUser method, along with a pre-generated user token, in order to authenticate the user. In a real-world application, your authentication backend would generate such a token at login / signup and hand it over to the mobile app. For more information, see the Tokens & Authentication page.
  • Step 4: We configure the ChannelListViewModelFactory with a filter and a sort option. We’re using the default sort option which orders the channels by last_updated_at time, putting the most recently used channels on the top. For the filter, we’re specifying all channels of type messaging where the current user is a member. The documentation about Querying Channels covers this in more detail.
  • Step 5: We bind our ChannelListView to the ChannelListViewModel by calling the bindView function.

Channel List Chat interface for Java / Kotlin on Android

Build and run your application - you should see the channel list interface shown on the right.

Creating a Chat Experience

Next, let's open up one of these channels and start chatting. To do this, we'll leverage the MessageListHeaderView, MessageListView, and MessageComposerView components.

Although our default components provide a robust experience, it's possible to configure and customize them, or even use your own custom views.

Create a new Empty Views Activity (New -> Activity -> Empty Views Activity) and name it ChannelActivity.

Make sure that ChannelActivity is added to your manifest. Android Studio does this automatically if you use the wizard to create the Activity, but you'll need to add it yourself if you manually created the Activity class.

Open up activity_channel.xml and change the layout to the following:

Next, replace the code in ChannelActivity with this code:

Configuring ChannelActivity involves a few steps, so let's review what's going on.

  • Step 1: We set up three ViewModels:
  • Step 2: We bind these ViewModels to their respective Views. This loose coupling between components makes it easy to customize things, or only use the components you find necessary.
  • Steps 3 and 4: We coordinate the MessageListView with both MessageListHeaderView and MessageComposerView. The MessageComposerView needs to know when you’re editing a message or when you enter a message thread, which is also a piece of useful information for MessageListHeaderView.
  • Steps 5 and 6: We create a back button handler, and set the same behavior for the MessageListHeaderView and the Activity's OnBackPressedDispatcher. The handler sends a BackButtonPressed event to the MessageListViewModel, which will decide how to handle this event. If we're in a message thread, it'll navigate back to the channel. If we're already in the channel, it will navigate to the channel list by emitting a NavigateUp state that we handle by finishing ChannelActivity.

Lastly, we want to launch ChannelActivity when you tap a channel in the channel list. Open MainActivity and replace the TODO at the end of the onCreate method:

If you run the application and tap on a channel, you'll now see the chat interface shown on the right.

Message List Chat interface for Java / Kotlin on Android

Chat Features

Congrats on getting your chat experience up and running! Stream Chat provides you with all the features you need to build an engaging messaging experience:

  1. Offline support: send messages, edit messages and send reactions while offline
  2. Link previews: generated automatically when you send a link
  3. Commands: type / to use commands like /giphy
  4. Reactions: long-press on a messages to add a reaction
  5. Attachments: use the paperclip button in MessageComposerView to attach images and files
  6. Edit message: long-press on your message for message options, including editing
  7. Threads: start message threads to reply to any message

You should also notice that, regardless of whether you chose to develop your app in Kotlin or Java, the chat loads very quickly. Stream’s API is powered by Go, RocksDB and Raft. The API tends to respond in less than 10ms and powers activity feeds and chat for over a billion end users.

Some of the features are hard to see in action with just one user online. You can open the same channel on the web and try user-to-user interactions like typing events, reactions, and threads.

Chat Message Customization

You now have a fully functional mobile chat interface. Not bad for a couple minutes of work! Maybe you'd like to change things up a bit though? No problem! Here are four ways to customize your chat experience:

  1. Style the MessageListView using attributes (easy)
  2. Create a custom attachment view (easy)
  3. Build your own views on top of the LiveData objects provided by the offline support library (advanced)
  4. Use the low level client to directly interact with the API

In the next sections, we'll show an example for each type of customization. We'll start by changing the colors of the chat messages to match your theme.

Open activity_channel.xml and customize the MessageListView with the following attributes for a green message style:

Customized Green Message List Chat interface for Java / Kotlin on Android

If you run the app and write a message, you'll notice that messages written by you are now green. The documentation for MessageListView details all the available customization options.

Creating Custom Attachment

There may come a time when you have requirements to include things in your chat experience that we don't provide out-of-the-box. For this purpose, we provide two main customization paths: you can either reimplement the entire ViewHolder and display a message how you like, or you can use custom attachment views, which is a lot less work. We'll look at this latter approach now.

You could use this to embed a shopping cart in your chat, share a location, or perhaps implement a poll. For this example, we'll keep it simple and customize the preview for images shared from Imgur. We're going to render the Imgur logo over images from the imgur.com domain.

As a first step, download the Imgur logo and add it to your drawable folder.

The Imgur logo

Next, create a new layout file called attachment_imgur.xml:

Now we need to create a custom implementation of AttachmentFactory. Create a new file called ImgurAttachmentFactory and add this code:

Let's break down what we're doing above:

  1. In canHandle, we check whether there's an Imgur attachment in the current message. Link previews in the Chat SDK are added to the message as attachments.
  2. If there is an Imgur attachment in the current message, createViewHolder will create the ImgurAttachmentViewHolder that inflates the custom Imgur layout, adds some styling (rounded corners), and then loads the Imgur image from the attachment's URL into the contained ImageView. We return this newly created View from the factory, and it'll be added to the message's UI.

Finally, we'll provide an instance of this AttachmentFactoryManager, which includes the ImgurAttachmentFactory to the MessageListView component. Open ChannelActivity and replace the TODO comment with the following:

Your Custom Attachment View

When you run your app, you should now see the Imgur logo displayed over images from Imgur. You can test this by posting an Imgur link like this one: https://imgur.com/gallery/ro2nIC6

This was, of course, a very simple change, but you could use the same approach to implement a product preview, shopping cart, location sharing, polls, and more. You can achieve lots of your message customization goals by implementing a custom attachment View.

If you need even more customization, you can also implement custom ViewHolders for the entire message object.

Imgur Logo overlay on the in-app messaging chat interface

Creating a Typing Status Component

If you want to build a custom UI, you can do that using the StateFlow objects provided by our offline support library, or the events provided by our low level client. The example below will show you how to build a custom typing status component using both approaches.

First, open activity_channel.xml and add the following TextView above the MessageListView. You'll also want to update the constraints for the MessageListView.

Option 1 - Typing Status Using the Offline Library

The offline support library enables you to watch a channel and fetch an instance of ChannelState, which provides observable StateFlow objects for a channel such as the current user, typing state, reads statuses, etc. The full list of StateFlow objects provided is detailed in the documentation. These make it easy to obtain data for use in your own custom UI.

Open ChannelActivity and add the following code below Step 6, still within the onCreate method (and an additional helper method for Java users):

In-app example of typing indicator on an Android messaging window

Remember to update your imports before running the app. You should now see a small typing indicator bar just below the channel header. Note that the current user is excluded from the list of typing users.

The code is quite simple - We watch the channel in order to get ChannelState, which contains an observable StateFlow called typing that provides us typing events.

If you're using Java, you'll notice an additional step that requires transforming StateFlows into LiveData. Coroutines are not commonly used in Java code so here we transform them into LiveData early to keep the codebase more familiar.

To test the behaviour, you can open a client on the web, enter the same channel, and then type away!

Option 2 - Typing Status Using the Low-Level Client

The low-level client enables you to talk directly to Stream's API. This gives you the flexibility to implement any messaging UI that you want. In this case, we want to show who is typing, current user included.

The entry point for the low-level client's APIs is the ChatClient class. In the code below, we get the ChatClient instance, and fetch a ChannelClient using the channel(cid) call. This provides access to all operations on the given channel.

Then, we use subscribeFor to listen to all TypingStart and TypingStop events in the current channel, and update the contents of the TextView with the list of typing users. Note that we specify the current Activity as the lifecycle owner to ensure that the event callbacks are removed when the Activity is no longer active.

In-app example of typing into an Android messaging window

Run your app and start typing in the MessageComposerView: you'll notice that the typing header on top updates to show that the current user is typing.

You can also use a web client to enter the same channel and generate typing events.


In this Android in-app messaging tutorial, you learned how to build a fully functional chat app using Java or Kotlin. You also learned how easy it is to customize the behavior and build any type of chat or messaging experience.

Remember, you can also check out the completed app for the tutorial on GitHub.

If you want to get started on integrating chat into your own app, sign up for a free Chat trial, and get your own API key to build with!

To recap, our Android Chat SDK consists of three libraries which give you an opportunity to interact with Stream Chat APIs on a different level:

  • stream-chat-android-client - The official low-level Android SDK for Stream Chat. It allows you to make API calls and receive events whenever something changes on a user or channel that you’re watching.
  • stream-chat-android-offline - Builds on top of the low-level client, adds seamless offline support, optimistic UI updates (great for performance) and exposes StateFlow objects. If you want to build a fully custom UI, this library is your best starting point.
  • stream-chat-android-ui-components - Provides ready-to-use UI components while also taking advantage of the offline library and low level SDK. This allows you to ship chat in your application in a matter of days.

The underlying chat API is based on Go, RocksDB, and Raft. This makes the chat experience extremely fast with response times that are often below 10ms.

Final Thoughts

In this chat app tutorial we built a fully functioning Android messaging app with our Android SDK component library. We also showed how easy it is to customize the behavior and the style of the Android chat app components with minimal code changes.

Both the chat SDK for Android and the API have plenty more features available to support more advanced use-cases such as push notifications, content moderation, rich messages and more. Please check out our Flutter tutorial too. If you want some inspiration for your app, download our free chat interface UI kit.

Give us Feedback!

Did you find this tutorial helpful in getting you up and running with Android for adding chat to your project? Either good or bad, we’re looking for your honest feedback so we can improve.

Kiddom logo

We’ve been going at lightspeed to build more communication functionality into Kiddom. The only way to achieve this in four months was to do a chat integration with Stream because we needed to do it reliably and at scale.

Head of Product, Kiddom profile picture

Nick Chen

Head of Product, Kiddom

Next Steps

Create your free Stream account to try out all our Chat product has to offer. No commitment or credit card required. If you want a custom plan or have questions, we are eager to talk with you.

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