PubSub - Android

The PubSub feature allows participants to send and receive messages on the topics they have subscribed to.

Methods

publish(), subscribe() and unsubscribe() are regular functions, not suspend functions. They throw VideoSDKException when a call is refused, for example before the meeting is joined or while it is reconnecting.

publish()

This method is used to publish a message to a specific topic.

Syntax

fun publish(topic: String, message: String, options: PubSubPublishOptions? = null, payload: JSONObject? = null)

Parameter Name	Type	Description
topic	String	This should be the topic for which you are publishing a message.
message	String	This is the actual message, which will be published to participants, who had subscribed to a particular topic.
options	PubSubPublishOptions?	This is an object of PubSubPublishOptions, which provides an option, such as persist, which persists message history for upcoming participants.
payload	JSONObject?	Optional data sent along with the message.

Example

private fun sendMessage() {
  val options = PubSubPublishOptions()
  options.setPersist(true)
  try {
    meeting!!.pubSub.publish("CHAT", "Hello from Android", options)
  } catch (e: VideoSDKException) {
    Log.e("#message", "publish failed: ${e.code} ${e.name}")
  }
}

subscribe()

This method is used to subscribe to a particular topic. Messages which were sent earlier with persist set arrive on the listener's onOldMessagesReceived(), in one or more batches.

Syntax

fun subscribe(topic: String, listener: PubSubMessageListener, options: PubSubSubscribeOptions? = null)

Parameter Name	Type	Description
topic	String	This should be the topic to be subscribed.
listener	PubSubMessageListener	This is an object of PubSubMessageListener, which listens for upcoming messages and calls onMessageReceived function, when new message received.
options	PubSubSubscribeOptions?	Optional. Limits how many old messages are delivered, for example with setOldMessageLimit().

Example

val pubSubMessageListener = object : PubSubMessageListener {
    override fun onMessageReceived(message: PubSubMessage) {
        Log.d("#message", "onMessageReceived: ${message.message}")
    }
    override fun onOldMessagesReceived(messages: List<PubSubMessage>, info: PubSubHistoryInfo) {
        // Persisted message list, in batches. info.isLast marks the last batch.
        Log.d("#message", "onOldMessagesReceived: $messages")
    }
}

override fun onCreate(savedInstanceState: Bundle?) {
  //...

  // Subscribe for 'CHAT' topic
  try {
    meeting!!.pubSub.subscribe("CHAT", pubSubMessageListener)
  } catch (e: VideoSDKException) {
    Log.e("#message", "subscribe failed: ${e.code} ${e.name}")
  }
}

unsubscribe()

This method is used to unsubscribe from a topic.

Syntax

fun unsubscribe(topic: String, listener: PubSubMessageListener)

Parameter Name	Type	Description
topic	String	This should be the topic to be unsubscribed.
listener	PubSubMessageListener	This is an object of PubSubMessageListener, which was passed in subscribe().

Example

fun unsubscribe() {
  // Unsubscribe 'CHAT' topic
  try {
    meeting!!.pubSub.unsubscribe("CHAT", pubSubMessageListener)
  } catch (e: VideoSDKException) {
    Log.e("#message", "unsubscribe failed: ${e.code} ${e.name}")
  }
}

Sample Code

package live.videosdk.rtc.android.kotlin

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import live.videosdk.rtc.android.Meeting
import live.videosdk.rtc.android.lib.PubSubMessage
import live.videosdk.rtc.android.lib.VideoSDKException
import live.videosdk.rtc.android.listeners.PubSubMessageListener
import live.videosdk.rtc.android.model.PubSubHistoryInfo
import live.videosdk.rtc.android.model.PubSubPublishOptions

class ChatActivity : AppCompatActivity() {

    // Meeting
    var meeting: Meeting? = null

    // PubSubMessageListener
        val pubSubMessageListener = object : PubSubMessageListener {
        override fun onMessageReceived(message: PubSubMessage) {
            Log.d("#message", "onMessageReceived: ${message.message}")
        }
        override fun onOldMessagesReceived(messages: List<PubSubMessage>, info: PubSubHistoryInfo) {
            // Persisted message list
            Log.d("#message", "onOldMessagesReceived: $messages")
        }
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_chat)

        /**
         * Here, we have created 'MainApplication' class, which extends android.app.Application class.
         * It has Meeting property and getter and setter methods of Meeting property.
         * In your android manifest, you must declare the class implementing android.app.Application (add the android:name=".MainApplication" attribute to the existing application tag):
         * In MainActivity.kt, we have set Meeting property, and joined the meeting.
         *
         * For Example: (MainActivity.kt)
         * val meeting = VideoSDK.initMeeting(context, meetingId, participantName, micEnabled, webcamEnabled, participantId, mode, multiStream, customTracks, metaData)
         * (this.application as MainApplication).meeting = meeting
        */

        // Get Meeting
        meeting = (this.application as MainApplication).meeting

        try {
            // Subscribe for 'CHAT' topic
            meeting!!.pubSub.subscribe("CHAT", pubSubMessageListener)

            sendMessage()
        } catch (e: VideoSDKException) {
            Log.e("#message", "PubSub call failed: ${e.code} ${e.name}")
        }
    }

    private fun sendMessage() {
      val options = PubSubPublishOptions()
      options.setPersist(true)
      meeting!!.pubSub.publish("CHAT", "Hello from Android", options)
    }

    override fun onDestroy() {
      try {
        // Unsubscribe for 'CHAT' topic
        meeting!!.pubSub.unsubscribe("CHAT", pubSubMessageListener)
      } catch (e: VideoSDKException) {
        Log.e("#message", "unsubscribe failed: ${e.code} ${e.name}")
      }
      super.onDestroy()
    }
}