Notify Attendees in Realtime - Android

During a livestream, you may want to broadcast a message to all the viewers at once.

Let's see how to use PubSub to implement this. If you are not familiar with the PubSub mechanism, you can follow this guide.

Notifying Attendees

1. Publish the message that the sender typed in the EditText field to the topic NOTIFY_ATTENDEES. publish() is a suspend function, so call it from a coroutine. It throws a VideoSDKException when the room is not joined, is RECONNECTING, or the message could not be sent, so wrap it in try/catch.

class SpeakerActivity : AppCompatActivity() {
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    //...
    findViewById<View>(R.id.btnSend).setOnClickListener { sendMessage() }
  }

  private fun sendMessage() {
    // get message from EditText
    val message: String = etmessage.getText().toString()
    if (!TextUtils.isEmpty(message)) {
        val publishOptions = PubSubPublishOptions(persist = true)

        lifecycleScope.launch {
            try {
                // Sending the Message using the publish method
                room!!.pubSub.publish("NOTIFY_ATTENDEES", message, publishOptions)

                // Clearing the message input
                etmessage.setText("")
            } catch (e: VideoSDKException) {
                // Room is not joined yet, is reconnecting, or the message could not be sent
                Toast.makeText(
                    this@SpeakerActivity, "Can't send right now, please try again",
                    Toast.LENGTH_SHORT
                ).show()
            }
        }
    } else {
        Toast.makeText(
            this@SpeakerActivity, "Please Enter Message",
            Toast.LENGTH_SHORT
        ).show()
    }
  }
}

2. Now let us show an alert to all the viewers displaying the message posted by the speaker. Subscribe to the topic from onRoomJoined(), so the subscription is made once the viewer has joined the room. subscribe() is a suspend function, so launch a coroutine for it.

caution

subscribe() requires a joined room. Called before the join completes, for example directly in onCreate() of the activity that joins the room, it throws a VideoSDKException with code 3035 (ERROR_ACTION_PERFORMED_BEFORE_ROOM_JOINED).

class ViewerActivity : AppCompatActivity() {

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

  private val roomEventListener = object : RoomEventListener() {
    override fun onRoomJoined(switchRoomId: String?) {
        // Subscribe for 'NOTIFY_ATTENDEES' topic once the room is joined
        lifecycleScope.launch {
            try {
                room!!.pubSub.subscribe("NOTIFY_ATTENDEES", pubSubMessageListener)
            } catch (e: VideoSDKException) {
                Log.d("VideoSDK", "subscribe failed: ${e.code} ${e.message}")
            }
        }
    }
  }

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

    //...

    // Add the listener before the viewer joins the room
    room!!.addEventListener(roomEventListener)
  }
}

note

onRoomJoined() also fires after a reconnect that needed a fresh join, and after switchTo(). The subscription is kept in both cases, so subscribing again with the same listener throws 3073 (ERROR_INVALID_PARAMETER). The catch above handles it.

API Reference

The API references for all the methods and events utilised in this guide are provided below.

• pubSub
• publish()
• subscribe()
• PubSubMessageListener
• onRoomJoined()