PubSub Class Methods - Flutter

publish()

• publish() is used to publish messages on a specified topic in the room.

Parameters

• topic

  • type: String
  • This is the name of the topic, for which message will be published.

• message

  • type: String
  • This is the actual message.

• options

  • type: PubSubPublishOptions
  • OPTIONAL
  • This specifies the options for publish. If you leave it out, the message is not stored and goes to everyone subscribed to the topic.

• payload

  • type: Map<String,dynamic>
  • OPTIONAL
  • If you need to include additional information along with a message, you can pass here as Map<String, dynamic>. It comes after options, so pass options too when you send a payload.

Returns

• Future<void>

Example

// Publishing message
try {
  await room.pubSub.publish(
    "CHAT",
    "Hii",
    const PubSubPublishOptions(persist: true),
  );

  // With a payload, which comes after the options
  await room.pubSub.publish(
    "CHAT",
    "Hii",
    const PubSubPublishOptions(persist: true),
    {"type": "greeting"},
  );
} on VideoSDKError catch (e) {
  print("publish failed: ${e.code} ${e.name}");
} catch (e) {
  // Anything else that went wrong.
  print("publish failed: $e");
}

caution

publish() needs a joined room. Called before Events.roomJoined fires, or after Events.roomLeft fires, it throws a VideoSDKError with code 3035.

When the SDK refuses the message, publish() throws a VideoSDKError, for example 3065 (ERROR_ROOM_RECONNECTING) while the room reconnects, or 4087 (PUBSUB_PUBLISH_FAILED) when the message cannot be sent. A 4087 failure also reaches Events.error. A failure that happens after publish() has completed reaches only Events.error, with code 4087.

---

subscribe()

• subscribe() is used to subscribe to a topic and receive its messages.

• Each PubSubMessageListener is its own subscription, with its own options. The topic's stored messages, published with persist: true, arrive on its onOldMessagesReceived. New messages arrive on its onMessageReceived.

Parameters

• topic:

  • type: String
  • Participants can listen to messages on that particular topic.

• listener:

  • type: PubSubMessageListener
  • The callbacks that receive the topic's messages. Every callback is optional.

• options:

  • type: PubSubSubscribeOptions
  • OPTIONAL
  • How many stored messages to deliver, and what to do when live messages arrive faster than the app takes them. A field you leave out takes the server's default.

Returns

• Future<void>

Example

// Subscribing 'CHAT' Topic
final chatListener = PubSubMessageListener(
  onMessageReceived: (PubSubMessage message) {
    print(message.message);
  },
  onOldMessagesReceived: (List<PubSubMessage> messages, PubSubHistoryInfo info) {
    // Stored messages; info.isLast is true on the last delivery
  },
);

Future<void> subscribePubSubTopic() async {
  try {
    await room.pubSub.subscribe(
      "CHAT",
      chatListener,
      const PubSubSubscribeOptions(oldMessageLimit: 50),
    );
  } on VideoSDKError catch (e) {
    print("subscribe failed: ${e.code} ${e.name}");
  } catch (e) {
    // Anything else that went wrong.
    print("subscribe failed: $e");
  }
}

// Subscribe once the room is joined
room.on(Events.roomJoined, () {
  subscribePubSubTopic();
});

caution

subscribe() needs a joined room. Called before Events.roomJoined fires, or after Events.roomLeft fires, it throws a VideoSDKError with code 3035 and the listener is not registered. Subscribe from your Events.roomJoined handler.

Subscribing the same listener to the same topic twice throws a VideoSDKError with code 3073 (ERROR_INVALID_PARAMETER).

When the SDK refuses the subscription, subscribe() throws a VideoSDKError, for example 3065 (ERROR_ROOM_RECONNECTING) while the room reconnects, or 4088 (PUBSUB_SUBSCRIBE_FAILED). The listener is then not registered.

---

unsubscribe()

• unsubscribe() is used to stop a listener receiving a topic you subscribed to before.

Parameters

• topic:

  • type: String
  • This is the name of the topic to be unsubscribed.

• listener:

  • type: PubSubMessageListener
  • The same listener object that you passed to subscribe().

Returns

• Future<void>

Example

// Unsubscribing 'CHAT' topic
try {
  await room.pubSub.unsubscribe("CHAT", chatListener);
} catch (e) {
  // chatListener is removed even when this throws
  print("unsubscribe failed: $e");
}

caution

The listener stops receiving messages at once, even when unsubscribe() throws.

Telling the server needs a joined room. Once Events.roomLeft has fired, unsubscribe() throws a VideoSDKError with code 3035. In teardown code such as State.dispose(), where you cannot await, add a .catchError() handler to the call.

While the room reconnects it can throw a VideoSDKError with code 3065 (ERROR_ROOM_RECONNECTING), or 4089 (PUBSUB_UNSUBSCRIBE_FAILED) when the request fails.