Raise Hand using PubSub - Android

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

Implementing Raise Hand

1. Choose the topic every participant publishes and subscribes to for raised hands. This guide uses RAISE_HAND.
2. On the raiseHand button, publish any message to that specific topic. 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.

class MainActivity : AppCompatActivity() {

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

    //...

    findViewById<View>(R.id.btnRaiseHand).setOnClickListener { sendRaiseHandMessage() }
  }

  private fun sendRaiseHandMessage() {
    val publishOptions = PubSubPublishOptions(persist = false)

    lifecycleScope.launch {
        try {
            // Sending the Message using the publish method
            room!!.pubSub.publish("RAISE_HAND", "Raise Hand", publishOptions)
        } catch (e: VideoSDKException) {
            // Room is not joined yet, is reconnecting, or the message could not be sent
            Log.d("VideoSDK", "publish failed: ${e.code} ${e.message}")
        }
    }
  }
}

3. Now let us show an alert to all the participants showing who raised the hand. Subscribe to the topic from onRoomJoined(), so the subscription is made once the room is joined. 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 MainActivity : AppCompatActivity() {

  // PubSubMessageListener
    val pubSubMessageListener = object : PubSubMessageListener {
        override fun onMessageReceived(message: PubSubMessage) {
            Toast.makeText(
                this@MainActivity, "${message.senderName} just raised the hand",
                Toast.LENGTH_SHORT
            ).show()
        }
    }

  private val roomEventListener = object : RoomEventListener() {
    override fun onRoomJoined(switchRoomId: String?) {
        // Subscribe for 'RAISE_HAND' topic once the room is joined
        lifecycleScope.launch {
            try {
                room!!.pubSub.subscribe("RAISE_HAND", 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_main)

    //...

    room!!.addEventListener(roomEventListener)
    lifecycleScope.launch {
        try {
            room!!.join()
        } catch (e: VideoSDKException) {
            Log.d("VideoSDK", "join failed: ${e.code} ${e.message}")
        }
    }
  }
}

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()