Question

I just realized static events exist – and I’m curious how people use them. I wonder how the relative comparison holds up to static vs. instance methods. For instance, a static method is basically a global function. But I’ve always associated events with instances of objects and I’m having trouble thinking of them at the global level.

Here some code to refer to if it helps an explanation:

void Main()
{
    var c1 = new C1();
    c1.E1 += () => Console.WriteLine ("E1");
    C1.E2 += () => Console.WriteLine ("E2");
    c1.F1();
}

// <<delegate>>+D()
public delegate void D();

// +<<event>>E1
// +<<class>><<event>>E2
// +F()
//      <<does>>
//          <<fire>>E1
//          <<fire>>E2
public class C1
{
    public void F1()
    {
        OnE1();
        OnE2();
    }
    public event D E1;
    private void OnE1()
    {
        if(E1 != null)
        {
            E1();
        }
    }
    static public event D E2;
    static private void OnE2()
    {
        if(E2 != null)
        {
            E2();
        }
    }
}

Answer 1

Much of OOP can be thought of in terms of message passing.

A method call is a message from the caller to the callee (carrying the parameters) and a message back with the return value.

An event is a message from the source to the subscriber. There are thus potentially two instances involved, the one sending the message and the one receiving it.

With a static event, there is no sending instance (just a type, which may or may not be a class). There still can be a recipient instance encoded as the target of the delegate.