事件词典

Question

Is there anything in c# that you can use to create a collection of events like lists, hashsets, and a dictionary in this case? Thankyou.

Answer 1

Sure you can:

Dictionary<String, Delegate> m_events = new Dictionary<String, Delegate>();

In Jeff Richter's Book CLR via C# you can find a complete implementation of an EventSet class.

(Even if you don't have the book you can download the sample code from https://www.wintellect.com/wp-content/uploads/2017/09/CLR-via-C-4th-Edition-Code.zip . The class in question is in "Ch11-1-EventSet.cs".)

As far as the question goes what an event is:

Say you have this line of code in your class:

public event EventHandler<NewMailEventArgs> NewMail;

then the C# compiler will translate the line above into three constructs:

1. A private delegate field. (Something like: private EventHandler<NewMailEventArgs> NewMail;

2. A public add_Xxx method (where Xxx is the Event name) that interested subscribers can use to register a callback delegate with the event.

3. A public remove_Xxx method (where Xxx is the Event name) that subscribers can use to unregister from the event.

(All the gory details can be found in section 11.2 of aforementioned book.)

So in other words the 'thing' you can store in your Event collection class is just a plain old delegate nothing else.

Answer 2

An event is like a property or method; you cant store instances of them. You can use reflection, but this likely isn't what you want.

Did you mean you want to store a list of methods to call when your event is fired? Events already do that.

EDIT:

Ah, I think I get it now. If you just simply fire your event, only the B instances that want it will get it. If you pass into the event args the instance of A that fired the event, then the B instance will be able to tell where it came from. But a B will never get an event from an A that it didn't ask for an event.

EDIT:

Maybe not. You only want to fire an event on one of the B's? Make B implement an interface that has a callback method. Instead of firing an event, call the method on the correct instance of B.

Answer 3

You could use IList with out any trouble. Type T could be any type defined in .net or user defined class.