Accessing managers from game entities/components

Question

I'm designing an entity-component engine in C# right now, and all components need to have access to the global event manager, which sends off inter-entity events (every entity also has a local event manager).

I'd like to be able to simply call functions like this:

GlobalEventManager.Publish("Foo", new EventData());
GlobalEventManager.Subscribe("Bar", OnBarEvent);

without having to do this:

class HealthComponent
{
    private EventManager globalEventManager;

    public HealthComponent(EventManager gEM)
    {
        globalEventManager = gEM;
    }
}

// later on...
EventManager globalEventManager = new EventManager();
Entity playerEntity = new Entity();
playerEntity.AddComponent(new HealthComponent(globalEventManager));

How can I accomplish this?

Answer 1

Although your solution works, you are losing testability by using singleton. In addition you are highly coupled with your global objects. If you will ever think of unit tests for your new components, you will have specially prepare your GlobalEventManager and ensure that your tests are not run in parallel.

One option is to use Factory pattern. Something like:

 playerEntity.AddComponent(componentFactory.createHealth());

Or read about dependency injection frameworks.

Answer 2

Why not just use C#'s native event system? That way any components that want to subscribe to a component's events can do so from outside the class.

Answer 3

I solved it by creating a singleton called GlobalEventManager. It derives from the local EventManager class and I use it like this:

GlobalEventManager.Instance.Publish("Foo", new EventData());

Thanks Byte :p