Feature request: unsubscribe()

[alecxandrys]

Good day, Is it possible to add next feature: unsubscribe() I want to change subscription's list, but can't remove only one or few of them. So i have to use unsubscribeAll() and make subscribe() again.

With best wishes.

[are]

Hi! You can cancel a subscription by calling .cancel() on a specific subscription.

Example:

var subscription1 = pubnub.subscribe(channels: {'channel-a'});

await subscription1.cancel();

[alecxandrys]

Hello, I see two problem:

• I have to keep subscription object;
• cancel() unsubscribe all channels from this subscription.

In my case I add eventHandler by next code: pubnub! .subscribe(channels: _channelsList.toSet(), withPresence: false) .messages .listen(eventHandler);

However, for every changes, which remove channel, in _channelsList I have to unsubscribe and resubscribe again.

Also i would not keep excess objects for every channel.

[are]

The way the SDK is designed it is very cheap to create and destroy the Subscription objects, so it is not an expensive operation. Underneath it is managed in such a way that multiple subscriptions are not using separate resources, so this should be inexpensive.

In general I recommend grouping your long-lived subscriptions into one, but if you know that a subscription will be short-lived it can be a separate subscription.

It's important to manage your subscriptions especially in a Flutter app. It's important to be able to granularly destroy subscriptions and stream listeners in a Flutter app, and that is the reason this SDK was designed.

However, if you feel like this isn't fitting in your use-case and you want a more centralized approach, I can add a feature request for this. Also you can experiment with writing your own subscription manager if you have the time and resources, we greatly appreciate any contributions!

Here is a rough sketch of how the SubscriptionManager maybe implemented for your use case:

import 'package:async/async.dart' show StreamGroup;
import 'package:pubnub/pubnub.dart';

class SubscriptionManager {
  final Set<Subscription> _subscriptions = Set();
  final StreamGroup<Envelope> _group = StreamGroup.broadcast();
  final PubNub pubnub;

  SubscriptionManager(this.pubnub);

  Stream<Envelope> get messages => _group.stream;

  void subscribe(List<String> channels) {
    for (var channel in channels) {
      var sub = pubnub.subscribe(channels: {channel});
      _subscriptions.add(sub);
      _group.add(sub.messages);
    }
  }

  Future<void> unsubscribe(List<String> channels) async {
    var subsToRemove = _subscriptions
        .where((sub) => sub.channels.any(channels.contains))
        .toList();

    for (var sub in subsToRemove) {
      _subscriptions.remove(sub);
      _group.remove(sub.messages);
      await sub.cancel();
    }
  }
}

[alecxandrys]

Hello! Thanks, i think this solution can help me for a time.

But I don't know which subscription will be short or long lived, so I have to keep every channel in separated subscription. It can become problem in the future, with up scaling of program.