In this tutorial well learn how to create a chat client that communicates with a Socket.IO Node.JS chat server, with our native Android Client! If you want to jump straight to the code, its on GitHub. Otherwise, read on!
To follow along, start by cloning the repository: socket.io-android-chat.
The app has the following features:
- Sending a message to all users joining to the room.
- Notifies when each user joins or leaves.
- Notifies when an user start typing a message.
Socket.IO provides an event-oriented API that works across all networks, devices and browsers. Its incredibly robust (works even behind corporate proxies!) and highly performant, which is very suitable for multiplayer games or realtime communication.
The first step is to install the Java Socket.IO client with Gradle.
For this app, we just add the dependency to
We must remember adding the internet permission to
<!-- app/AndroidManifest.xml -->
Now we can use Socket.IO on Android!
First, we have to initialize a new instance of Socket.IO as follows:
IO.socket() returns a socket for
http://chat.socket.io with the default options. Notice that the method caches the result, so you can always get a same
Socket instance for an url from any Activity or Fragment.
And we explicitly call
onCreate lifecycle callback for that, but it actually depends on your application.
Sending data looks as follows. In this case, we send a string but you can do JSON data too with the org.json package, and even binary data is supported as well!
private EditText mInputMessageView;
Like I mentioned earlier, Socket.IO is bidirectional, which means we can send events to the server, but also at any time during the communication the server can send events to us.
We then can make the socket listen an event on
onCreate lifecycle callback.
With this we listen on the
new message event to receive messages from other users.
This is what
onNewMessage looks like. A listener is an instance of
Emitter.Listener and must be implemented the
call method. Youll notice that inside of
call() is wrapped by
Activity#runOnUiThread(), that is because the callback is always called on another thread from Android UI thread, thus we have to make sure that adding a message to view happens on the UI thread.
Since an Android Activity has its own lifecycle, we should carefully manage the state of the socket also to avoid problems like memory leaks. In this app, we’ll close the socket connection and remove all listeners on
onDestroy callback of Activity.
off() removes the listener of the
new message event.
If you want to explore more, I recommend you look into:
Other features of this app. They are just implemented with
The details of Socket.IO Java Client. It supports all the features JS client does.
Many other great Socket.IO implementations created by the community!