public interface IFoo<T>
{
    event Action<T> ChangeValue;
    event Action<object> ChangeObject;
    event Action ChangeEmpty;

    void InvokeChange(T value);
}

IFoo<int> test = new Foo<int>();
test.ChangeEmpty  += ()  => Console.WriteLine("0) Empty!");
test.ChangeObject += (o) => Console.WriteLine("1) Object: {0}", o);
test.ChangeValue  += (v) => Console.WriteLine("2) Value:  {0}", v);
test.ChangeObject += (o) => Console.WriteLine("3) Object: {0}", o);
test.ChangeEmpty  += ()  => Console.WriteLine("4) Empty!");
test.InvokeChange(123);

0) Empty!
1) Object: 123
2) Value:  123
3) Object: 123
4) Empty!

public static void Main()
{
    IFoo<int> test = new Foo<int>();

    test.ChangeEmpty += EmptyHandler;
    test.ChangeObject += ObjectHandler;
    Console.WriteLine("1) EMPTY, OBJECT");
    test.InvokeChange(1);

    test.ChangeEmpty -= EmptyHandler;
    test.ChangeValue += ValueHandler;
    Console.WriteLine("2) OBJECT, VALUE");
    test.InvokeChange(2);

    test.ChangeObject -= ObjectHandler;
    Console.WriteLine("3) VALUE ");
    test.InvokeChange(3);

    test.ChangeObject += ObjectHandler;
    test.ChangeEmpty += EmptyHandler;
    test.ChangeValue += ValueHandler;
    Console.WriteLine("4) VALUE, OBJECT, EMPTY, VALUE");
    test.InvokeChange(4);

    test.ChangeValue -= ValueHandler;
    test.ChangeValue -= ValueHandler;
    test.ChangeEmpty -= EmptyHandler;
    test.ChangeObject -= ObjectHandler;
    Console.WriteLine("5) <NONE>");
    test.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); }

1) EMPTY, OBJECT
  - Empty!
  - Object: 1
2) OBJECT, VALUE
  - Object: 2
  - Value: 2
3) VALUE
  - Value: 3
4) VALUE, OBJECT, EMPTY, VALUE
  - Value: 4
  - Object: 4
  - Empty!
  - Value: 4
5) <NONE>

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;
        }
    }
}