Publish–subscribe design pattern implementation framework, with an ability to publish events by topic.
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Publish–subscribe design pattern implementation framework, with ability to publish events by topic. (NotificationCenter extended alternative)

On Medium:


TopicEventBus Icon


TopicEventBus is Easy to use, type safe way of implementing Publish–subscribe design pattern.

There are many other libraries out there, aiming to solve this issue, but none of them support publishing events by topic, in a type-safe way, with no magic strings.

Also, TopicEventBus holds weak referenced for Its observers, so you don't have to be afraid of memory leaks.

What is a topic?

The topic is for example, when you would like to publish "ConversationUpdateEvent" yet have the ability to publish that event only to listeners with conversation id "1234" or to all listeners.

Specifying the conversation Id is specifying a topic for that event.

Show me the code! and what's in it for me.

Let's build a chat app!

In this app, we are going to have multiple conversations screens, each one of them would like to know only about changes to Its conversation.

The first step, create an event for conversation update:

class ConversationChangedEvent: TopicEvent {
    let newTitle: String
    init(conversationId: String, newTitle: String) {
        self.newTitle = newTitle
        self.key = conversationId

Every event must inherit from "TopicEvent," and in case it has a topic (Our example it will be the conversation id) set "key" property to the correct value.

Now inside ConversationVC, subscribe to this event:

Notice you only need to specify the return value you are expecting, for TopicEventBus to figure out the event you are subscribing for

class ConversationVC: UIViewController {
    let topicEventBus: TopicEventBus
    let conversationId = "1234"
    init(topicEventBus: TopicEventBus) {
        self.topicEventBus = topicEventBus
    override func viewDidLoad() {
        _ = self.topicEventBus.subscribe(topic: conversationId, callback: { (conversationChangedEvent: ConversationChangedEvent) in
            // This will run every time "ConversationChangedEvent" with id 1234 will be fired.

This is how you fire an event:

class FiringService {
    let topicEventBus: TopicEventBus
    init(topicEventBus: TopicEventBus) {
        self.topicEventBus = topicEventBus
    func conversationTitleChanged() { ConversationChangedEvent.init(conversationId: "1234",
                                                                                            newTitle: "First update"))

You did it! You fired your first event with topic 🤗 🎉


If you subscribe to event and specify no topic, you will receive all events from that type, no matter their key:

_ = self.topicEventBus.subscribe { (conversationChangedEvent: ConversationChangedEvent) in
  // All events from this type: ConversationChangedEvent will trigger this block

Unsubscribe by calling "stop" on the returned object after subscribing:

let listener = self.topicEventBus.subscribe(topic: conversationId, callback: { (conversationChangedEvent: ConversationChangedEvent) in

On app log out, terminate TopicEventBus by just calling:


Example project

Please notice example project contains tests to support all edge cases, plus example code from the above snippets.



TopicEventBus is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod 'TopicEventBus'


  1. Download and drop /TopicEventBus folder in your project.
  2. Congratulations!


Matan made this with ❤️.