Question

What is the syntax to return an event from a function? (Not to call the event, to return it so that it can be bound to functions).

I have a container class that contains a dictionary where each members has an event.

The aim is to be able to write something like this:

Container c = new Container();
c.CreateEventForKey("a");             // Create the member in the dictionary
c.EventForKey("a") += some_function;  // Bind some_function to the event in the "a" member
c.OnEventForKey("a","b");             // Calls some_function with argument "b"

The Container class looks like this:

public class Container {

  public class Member {
     public event Action<string> AnEvent;
     public void OnEvent( string v ) { if(AnEvent!=null) { AnEvent(v); } }
  }

  protected Dictionary<string,Member> members;

  // This seems to work OK.
  public void OnEventForKey(string k, string v) {
    if ( members.ContainsKey(k) ) { members[k].OnEvent(v); }
    else { /* report error */ }
  }

  // Can't get this to compile.
  public event Action<string> EventForKey(string k ) {
    if ( members.ContainsKey(k) ) { return members[k].AnEvent; }
    else { /* report error */ }
  }
}

How can I define EventForKey so that this does what I expect?

Answer 1

What is the syntax to return an event from a function?

You can’t, easily. Events – like properties – aren’t really first class “objects” as such; they’re members of a class. You don’t really have a class member here – you’re trying to just keep delegates in a dictionary.

You could create your own “event-like” container, but it’s probably better to consider alternative designs, e.g.

c.Subscribe("a", SomeFunction);
c.OnEventForKey("a");

You might want to look at EventHandlerList for inspiration.