c# - How to implement an event system

Im trying to implement an Event System for a game, where there are classes that can fire or handle an event wheter or not they implement these interfaces:

public interface IGameEvent where T : EventArgs
{

     event EventHandler OnEvent;
}

public interface IGameHandler where T : EventArgs
{
    void OnEvent(object sender, T e);
}

everything looked great until i realized that no class can implement more than 1 IGameEvent because it would cause duplicate declaration,

Here is an example:

public class Event
{
    public KeyPressEvent OnKeyPress;
    public UpdateEvent OnUpdate;

    public void AddHadler(IGameEvent eEvent , IGameHandler eHandler) where  T : EventArgs
    {
        eEvent.OnEvent += eHandler.OnEvent;
    }


    public void RemoveHandler(IGameEvent eEvent, IGameHandler eHandler) where T : EventArgs
    {
        eEvent.OnEvent -= eHandler.OnEvent;
    }
}

KeyPressEvent:

public class KeyPressEvent : IGameEvent
{
    public class KeyPressedEventArgs : EventArgs

    {
        public KeyPressedEventArgs(Keys key)
        {
            Key = key;
        }

        public Keys Key { get; private set; }
    }

    public event EventHandler OnEvent;


    private void OnCheckForKeyPressed()  //Example
    {
        if (OnEvent != null) 
            OnEvent(this, new KeyPressedEventArgs(Keys.Space));
    }
}

Would be better to manually store the suscribers in a list in the EventSystem ?

How slower or faster than this approach that would be?

Thanks!

Answer

Although you can use the existing event model in C#, it might not always give you the flexibility that you require.

You can for instance not sort events based on their priority, clear events of a specific type or add a queued/delayed event.

Example)

To signup for an event the object needs a method with the same signature as the CallbackMethod delegate. The call might look like this:

class SomeObject
{
    private void OnDamageTaken(object sender, IGameEvent e)

    {
        ...
    }

    ... void Initialize()
    {
        ...
        EventManager.Subscribe("EVENT_PLAYERINJURED", this.OnDamageTaken);
        ...
    }

}

//Somewhere in the application
EventManager.Notify("EVENT_PLAYERINJURED", new PlayerInjuredEvent(...));

If you don't like using hardcoded eventIds everywhere you could introduce a property on your game event classes.

public PlayerInjuredEvent : IGameEvent
{
    public static string EventType
    {

            get
            {
                return "EVENT_PLAYERINJURED";
            }
    }
}

Now you can write:

EventManager.Notify(PlayerInjuredEvent.EventType, ...

I hope this gives you some ideas on how to solve your problem.