using System;

using System.Collections.Generic;

​

public interface IFoo<T>

{

    event Action<T> ChangeValue;

    event Action<object> ChangeObject;

    event Action ChangeEmpty;

    void InvokeChange(T value);

}

​

public class Program

{

    public static void Main()

    {

        IFoo<int> test1 = new Foo<int>();

        test1.ChangeEmpty  += ()  => Console.WriteLine("0) Empty!");

        test1.ChangeObject += (o) => Console.WriteLine("1) Object: {0}", o);

        test1.ChangeValue  += (v) => Console.WriteLine("2) Value:  {0}", v);

        test1.ChangeObject += (o) => Console.WriteLine("3) Object: {0}", o);

        test1.ChangeEmpty  += ()  => Console.WriteLine("4) Empty!");

        test1.InvokeChange(123);

        Console.WriteLine("\n--------\n");

        IFoo<int> test2 = new Foo<int>();

​

        test2.ChangeEmpty += EmptyHandler;

        test2.ChangeObject += ObjectHandler;

        Console.WriteLine("1) EMPTY, OBJECT");

        test2.InvokeChange(1);

​

        test2.ChangeEmpty -= EmptyHandler;

        test2.ChangeValue += ValueHandler;

        Console.WriteLine("2) OBJECT, VALUE");

        test2.InvokeChange(2);

​

        test2.ChangeObject -= ObjectHandler;

        Console.WriteLine("3) VALUE ");

        test2.InvokeChange(3);

​

        test2.ChangeObject += ObjectHandler;

        test2.ChangeEmpty += EmptyHandler;

        test2.ChangeValue += ValueHandler;

        Console.WriteLine("4) VALUE, OBJECT, EMPTY, VALUE");

        test2.InvokeChange(4);

​

        test2.ChangeValue -= ValueHandler;

        test2.ChangeValue -= ValueHandler;

        test2.ChangeEmpty -= EmptyHandler;

        test2.ChangeObject -= ObjectHandler;

        Console.WriteLine("5) <NONE>");

        test2.InvokeChange(5);

    }

​

    static void EmptyHandler() { Console.WriteLine("  - Empty!"); }

    static void ObjectHandler(object val) { Console.WriteLine("  - Object: {0}", val); }

    static void ValueHandler(int val) { Console.WriteLine("  - Value: {0}", val); }

}

​

public class Foo<T> : IFoo<T>

{

    private EventProxyContainer<T> handlers;

​

    public event Action<T> ChangeValue  

    { 

        add { handlers.Add(value); } 

        remove { handlers.Remove(value); } 

    }

​

    public event Action<object> ChangeObject 

    { 

        add { handlers.Add(value); } 

        remove { handlers.Remove(value); } 

    }

​

    public event Action ChangeEmpty 

    { 

        add { handlers.Add(value); } 

        remove { handlers.Remove(value); } 

    }

​

    public void InvokeChange(T value) 

    {

        foreach(Action<T> a in handlers.GetInvocationList())

            a.Invoke(value);

    }

}

​

public struct EventProxyContainer<T>

{

    private event Action<T> handlers;

    private struct EventProxy

    {

        public Action<T> proxy;

        public int count;

    }

    private Dictionary<object, EventProxy> proxies;

    public void Add(object handler)

    {

        if(handler == null) return;

        if(proxies == null) proxies = new Dictionary<object, EventProxy>();

        EventProxy entry;

        if(proxies.TryGetValue(handler, out entry))

        {

            entry.count += 1;

            proxies[handler] = entry;

        }

        else

        {

            entry = new EventProxy() { count = 1 };

            if(handler is Action<T>) 

                entry.proxy = (Action<T>)handler;

            else if(handler is Action<object>) 

                entry.proxy = (v) => ((Action<object>)handler).Invoke(v);

            else if (handler is Action) 

                entry.proxy = (v) => ((Action)handler).Invoke();

            proxies.Add(handler, entry);

        }

        handlers += entry.proxy;

    }

    public void Remove(object handler)

    {

        if(handler == null || proxies == null) return;

        EventProxy entry;

        if(proxies.TryGetValue(handler, out entry))

        {

            handlers -= entry.proxy;

            entry.count -= 1;

            if(entry.count == 0) 

                proxies.Remove(entry);

            else

                proxies[handler] = entry;

        }

    }

    public Delegate[] GetInvocationList()

    {

        return handlers == null ? new Delegate[0] : handlers.GetInvocationList();

    }

}

​

​

​