MessageHub

An implementation of the Event Aggregator Pattern.

NuGet package:

Usage example:

Start by getting the singleton instance of the hub:

var hub = MessageHub.Instance;

You can now use the hub to subscribe to any publication of a given type:

var token = hub.Subscribe<Person>(p => Console.WriteLine($"Id is: {p.Id}"));
// or    
Action<string> action = message => Console.WriteLine($"Message is: {message}");
var anotherToken = hub.Subscribe(action);

You can then use the token to do:

hub.IsSubscribed(token); // returns true
hub.UnSubscribe(token);
hub.IsSubscribed(token); // returns false

Or you can clear all subscriptions by:

hub.ClearSubscriptions();

Publication is as easy as:

hub.Publish(new Person { Id = "Foo" });
hub.Publish("An important message");

Error handling:

The hub catches any exception thrown at the time of publication and exposes them by:

hub.OnError += (sender, eArgs)
        => Console.WriteLine($"Error Publishing, Token: {eArgs.Token} | Exception: {eArgs.Exception}");

Global handler:

The hub allows the registration of a single handler which will receive every message published by the hub. This can be useful in scenarios where every message published should be logged or audited.

hub.RegisterGlobalHandler((type, eventObject) => Console.WriteLine($"Type: {type} - Event: {eventObject}"));

Inheritance support:

The hub supports inheritance by allowing to subscribe to a base class or an interface and receiving all the publications of types that inherit or implement the subscribed type. For example, given:

public class Order {}
public class NewOrder : Order{}
public class BigOrder : Order{}

A subscriber registering against Ordrer will also receive events of type NewOrder and BigOrder.

Reference:

#1. http://www.nimaara.com/2016/02/14/cleaner-pub-sub-using-the-event-aggregator-pattern/

#2. https://github.com/NimaAra/Easy.MessageHub/

#3. https://www.codeproject.com/Articles/866547/Publisher-Subscriber-pattern-with-Event-Delegate-a/