PubSub - Flutter

PubSub feature allows the participant to send and receive messages of the topics which he has subscribed.

Methods

publish()

This method is use for publishing message of specific topic.

Syntax

  Future<void> publish(
    String topic,
    String message,
    [PubSubPublishOptions options]
  )

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.

Example

  // publish()
  ElevatedButton(
    onPressed: () async {
      // Publish a message
      await meeting.pubSub.publish(
        "CHAT", // Topic
        "Hello from Flutter!", // Message Content
        const PubSubPublishOptions(
          "persist": true // Stores the message in server for future participants
        ),
      );

      print("Message published");
    },
    child: Text("Publish"),
  ),

subscribe()

This method is used to subscribe for particular topic. This method returns a list of messages which were sent earlier.

Syntax

  Future<PubSubMessages> subscribe(
    String topic,
    Function(PubSubMessage) messageHandler,
  )

Parameter Name	Type	Description
topic	String	This should be the topic to be subscribed.
messageHandler	String	This is a handler function, which will be called when new message received.

Example

  // subscribe()
  ElevatedButton(
    onPressed: () async {
      // Subscribe 'CHAT' topic and get persisted messages
      var messages = await meeting.pubSub.subscribe("CHAT", messageHandler);

      // Printing message list
      print("Messages: ${messages.messages.map((msg) => msg.message).join(" ")}");
    },
    child: Text("Subscribe"),
  ),

  // Message Handler
  void messageHandler(msg){
    // Do something
    print("New message received: $msg");
  }

unsubscribe()

This method is used to unsubscribe the message topic.

Syntax

  Future<void> unsubscribe(
    String topic,
    Function(PubSubMessage) messageHandler,
  )

Parameter Name	Type	Description
topic	String	This should be the topic to be unsubscribed.
messageHandler	String	This is a handler function, which was passed in subscribe().

Example

  // unsubscribe
  ElevatedButton(
    onPressed: () {
      // Unsubscribe 'CHAT' topic
      await meeting.pubSub.unSubscribe("CHAT", messageHandler);
    },
    child: Text("UnSubscribe"),
  ),

Sample Code

import 'package:flutter/material.dart';
import 'package:videosdk/rtc.dart';

// ChatScreen
class ChatScreen extends StatefulWidget {
  final Meeting meeting;
  const ChatScreen({required this.meeting});

  @override
  _ChatScreenState createState() => _ChatScreenState();
}

class _ChatScreenState extends State<ChatScreen> {
  @override
  void initState() {
    super.initState();

    widget.meeting.pubSub.subscribe("CHAT", messageHandler)
      .then((messages) =>
          print("Subscribed to chat: ${messages.messages.map((msg) => msg.message).join(" ")}"));
  }

  @override
  Widget build(BuildContext context) {
    final meeting = widget.meeting;
    return Scaffold(
      appBar: AppBar(title: const Text("PubSub Sample Code")),
      body: Center(
        child: ElevatedButton(
          child: const Text("Send Hello !"),
          // Publish Hello message
          onPressed: () => meeting.pubSub.publish(
            "CHAT",
            "Hello",
            const PubSubPublishOptions(persist: true),
          ),
        ),
      ),
    );
  }

  // Handle incoming messages
  void messageHandler(PubSubMessage message) {
    print("New message: ${message.message}");
  }

  @override
  void dispose() {
    // Unsubscribe
    widget.meeting.pubSub.unsubscribe("CHAT", messageHandler);
    super.dispose();
  }
}