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Version: 2.0.x

PubSub - iOS

PubSub is a short acronym for Publish-Subscribe mechanism. This mechanism is used to send and recieve messages from a particular topic. As the name suggests, for someone to send a message, they have to specify the topic and the message which should be published and for someone to receive a message, they should be subscribed to that topic.

Here is a visual to better understand publish-subscribe mechanism.



In order to use PubSub in meeting, VideoSDK provides a class pubSub which allows you to subscribe to any topic and publish to any topic allowing to pass on messages and instructions during the meeting easily.


  • This method is used for publishing message of specific topic.
  • This method can be accessed from the pubSub class, which is subclass of Meeting class.
  • This method will accept following parameters as input:
    • topic: This will be the topic for which you are publishing a message.
    • message: This will be the actual message to be published. It has to be in String format.
    • options: This is an object of PubSubPublishOptions which specifies the options for publish. PubSubPublishOptions has 2 properties.
      • persist : persist offered the option of keeping the message around for the duration of the session. When persist is set to true, that message will be retained for upcoming participants and will be available in VideoSDK Session Dashboard with .CSV format after completion of session.
      • sendOnly: If you want to send a message to specific participants, you can pass their respective participantId in form of String[]. If you don't provide any IDs or pass a null value, the message will be sent to all participants by default. This is optional parameter.
  //Button that will send the message when tapped
@IBAction func sendMessageTapped(_ sender: Any) {
let options = ["persist" : true]
// publish message
self.meeting?.pubsub.publish(topic: "CHAT", message: "How are you?", options: options)


  • This method is used to subscribe for particular topic.

  • This method will accept two parameters as input:

    • topic: This will be the topic to be subscribed.
    • listener: This is an object of PubSubMessageListener, which listens for upcoming messages and calls onMessageReceived function, when new message is received.
  • This method will return List<PubSubMessage> which is a list of messages which were sent earlier.

The object of PubSubMessage contains following properties:

  • senderId: This represents the participantId of the participant who send the message.
  • senderName: This represents the displayName of the participant who send the message.
  • message: This will be the actual message that was send.
  • timestamp: This wil the timestamp for when the message was published.
  • topic: This will be the name of the topic message was published to.
extension MeetingViewController: MeetingEventListener {

/// Meeting started
func onMeetingJoined() {

// listen/subscribe for chat topic
meeting?.pubsub.subscribe(topic: "CHAT", forListener: self)


  • This method is used to unsubscribe for particular topic.

  • This method will accept two parameters as input:

    • topic: This will be the topic to be unsubscribed.
    • listener: This is an object of PubSubMessageListener, which was passed in subscribe().
func unsubscribe() {
// Unsubscribe 'CHAT' topic
meeting?.pubSub.unsubscribe("CHAT", pubSubMessageListener)

Applications of usePubSub

PubSub is a very powerful mechanism which can be used to do alot of things which can make your meeting experience much more interactive. Some of the most common usecase that we have come across for the PubSub during a meeting are listed below:

  1. Chat: You can utilise this to develop various Chat features, such as Private Chat and Group Chat. You can follow our chat integration guide here.
  2. Raise Hand: You can allow attendees to raise their hands at any time during the meeting, informing everyone else that someone has done so.
  3. Poll: You may make polls, let users respond to them, and display the results at the end of a poll.
  4. Question Answer Session: You can also design interactive functionality that is question-and-answer based.

Downloading PubSub Messages

All the messages from the PubSub which were published with persist : true and can be downloaded as an .csv file. This file will be available in the VideoSDK dashboard as well as throught the Sessions API.

API Reference

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

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