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>

{

    public event Action<T> ChangeValue = delegate {};

​

    private Dictionary<System.Action<object>, List<System.Action<T>>> ObjectEventProxies

        = new Dictionary<System.Action<object>, List<System.Action<T>>>();

    public event System.Action<object> ChangeObject

    {

        add

        {

            List<System.Action<T>> eventProxies;

            if(!ObjectEventProxies.TryGetValue(value, out eventProxies))

            {

                eventProxies = new List<System.Action<T>>();

                ObjectEventProxies.Add(value, eventProxies);

            }

            System.Action<T> proxy = (T v) => value.Invoke(v);

            eventProxies.Add(proxy);

            ChangeValue += proxy;

        }

        remove

        {

            List<System.Action<T>> eventProxies;

            if (ObjectEventProxies.TryGetValue(value, out eventProxies))

            {

                System.Action<T> proxy = eventProxies[eventProxies.Count - 1];

                eventProxies.RemoveAt(eventProxies.Count - 1);

                ChangeValue -= proxy;

            }

        }

    }

    private Dictionary<System.Action, List<System.Action<T>>> EmptyEventProxies

        = new Dictionary<System.Action, List<System.Action<T>>>();

    public event System.Action ChangeEmpty

    {

        add

        {

            List<System.Action<T>> eventProxies;

            if(!EmptyEventProxies.TryGetValue(value, out eventProxies))

            {

                eventProxies = new List<System.Action<T>>();

                EmptyEventProxies.Add(value, eventProxies);

            }

            System.Action<T> newProxy = (T v) => value.Invoke();

            eventProxies.Add(newProxy);

            ChangeValue += newProxy;

        }

        remove

        {

            List<System.Action<T>> eventProxies;

            if (EmptyEventProxies.TryGetValue(value, out eventProxies))

            {

                System.Action<T> proxy = eventProxies[eventProxies.Count - 1];

                eventProxies.RemoveAt(eventProxies.Count - 1);

                ChangeValue -= proxy;

            }

        }

    }

    public void InvokeChange(T value)

    {

        ChangeValue.Invoke(value);

    }

}