Subscribe with Android

This guide shows how to use the WebSocket API with Android using Java or Kotlin.

We will be using OkHttp library to achieve this.

Start by creating a new dummy project in Android studio (Kotlin or Java, any), then follow the steps below.

Add dependency

Let's start by adding OkHttp as a dependency to our application. Add the following code into your module-level build.gradle file

implementation 'com.squareup.okhttp3:okhttp:3.6.0'

Add permissions

It is mandatory to have internet access permissions to connect to our server, so make sure you have added the following in your manifest. If not, copy the following code and paste it before the application tag

<uses-permission android:name="android.permission.INTERNET" />

Also, you need to allow clear-text traffic. To do so, add the following attribute on your application tag

android:usesCleartextTraffic="true"

Your application tag should look something like this

<uses-permission android:name="android.permission.INTERNET" />

<application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"        
        android:theme="@style/AppTheme"
        android:usesCleartextTraffic="true">

Add the PieSocketListener class

Copy the following code and paste it into a file named PieSocketListener.java in the same directory as MainActivity.kt in your application.

package com.example.myapplication;

import android.util.Log;

import okhttp3.Response;
import okhttp3.WebSocket;
import okhttp3.WebSocketListener;

public class PieSocketListener extends WebSocketListener {

    private static final int NORMAL_CLOSURE_STATUS = 1000;

    @Override
    public void onOpen(WebSocket webSocket, Response response) {
        webSocket.send("Hello World!");
    }

    @Override
    public void onMessage(WebSocket webSocket, String text) {
        output("Received : " + text);
    }

    @Override
    public void onClosing(WebSocket webSocket, int code, String reason) {
        webSocket.close(NORMAL_CLOSURE_STATUS, null);
        output("Closing : " + code + " / " + reason);
    }

    @Override
    public void onFailure(WebSocket webSocket, Throwable t, Response response) {
        output("Error : " + t.getMessage());
    }

    public void output(String text){
        Log.d("PieSocket",text);
    }

}

Add UI

Let's add a simple button, clicking which will connect you to the PieSocket channel. Open your activity_main.xml file and replace its contents with this.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/connect"
        style="@android:style/Widget.Holo.Light.Button"
        android:layout_width="333dp"
        android:layout_height="85dp"
        android:layout_centerInParent="true"
        android:text="Connect to PieSocket"
        android:textSize="17sp" />

</RelativeLayout>

Time to connect!

New Android studio projects create MainActivity.kt by default instead of MainActivity.java, so the following example is in Kotlin.

Open your MainActivity.kt file and replace the onCreate method with the following code

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    val client: OkHttpClient =  OkHttpClient();

    connect.setOnClickListener{
        Log.d("PieSocket","Connecting");
        var apiKey = "oCdCMcMPQpbvNjUIzqtvF1d2X2okWpDQj4AwARJuAgtjhzKxVEjQU6IdCjwm"; //Demo key, get yours at https://piesocket.com
        var channelId = 1;

        val request: Request = Request
            .Builder()
            .url("wss://demo.websocket.me/v3/$channelId?api_key=$apiKey&notify_self")
            .build()
        val listener = PieSocketListener()
        val ws: WebSocket = client.newWebSocket(request, listener)
    }
}

The MainActivity.kt file in your project should look like this

package com.example.myapplication

import android.os.Bundle
import android.util.Log
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
import okhttp3.OkHttpClient
import okhttp3.Request
import okhttp3.WebSocket

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val client: OkHttpClient =  OkHttpClient();

        connect.setOnClickListener{
            Log.d("PieSocket","Connecting");
            var apiKey = "oCdCMcMPQpbvNjUIzqtvF1d2X2okWpDQj4AwARJuAgtjhzKxVEjQU6IdCjwm";
            var channelId = 1;

            val request: Request = Request
                .Builder()
                .url("wss://demo.websocket.me/v3/$channelId?api_key=$apiKey&notify_self")
                .build()
            val listener = PieSocketListener()
            val ws: WebSocket = client.newWebSocket(request, listener)
        }
    }

}

Testing

Run the application, open Logcat, and in the search-box that filters out log messages, type PieSocket, to filter out log messages we are interested in.

Now, click on Connect to PieSocket button in the application and you should start to see the logs coming from the WebSocket channel.

Help

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