delegate with generic type

Question

I have a delegate public delegate void ObserverCallback<T>(T value, string key); which I want the value parameter to be whatever I want.

I have an ObserverCallback property in my class public ObserverCallback Callback; which obviously gives me this error error CS0305: Using the generic type 'Observer.ObserverCallback<T>' requires 1 type arguments. At this point, I do not know what type will be the parameter.

I would like to fix that error and to be able to pass a function through a contructor e.g. :

• public Observer(ObserverCallback<???> callback)
• private void ACallbackFunction(Player value)
• var obs = new Observer(ACallbackFunction)

Answer 1

Your observer class has to be generic, and then you can use that parameter in the constructor:

public class Observer<T>
{
    public Observer(ObserverCallback<T> callback)
    {    

    }
}

Usage:

var obs = new Observer<Player>(ACallbackFunction);

If you need to use Observer as a non-generic, you could inherit from a non-generic base or implement a common interface. The caveat here is that the methods using the class generic argument T won't be available unless you explicitly cast it back to Observable<T>:

public class Observer
{
    public void SomeMethod()
    {

    }
}

public class Observer<T>
{
    public Observer(ObserverCallback<T> callback)
    {
    }
}

var observerList = new List<Observer>();
observerList.Add(new Observer<Player>(ACallbackFunction));
observerList.ForEach(o => o.SomeMethod());

or

public interface IObserver
{
    void SomeMethod();
}

public class Observer<T>: IObserver
{
    public Observer(ObserverCallback<T> callback)
    {
    }

    public void SomeMethod()
    {
    }
}

var observerList = new List<IObserver>();
observerList.Add(new Observer<Player>(ACallbackFunction));
observerList.ForEach(o => o.SomeMethod());

Note that this generic argument T will be available to any method in the class, so you don't have to write public void MyMethod<T>(T value) (which declares a generic argument T), you can then just write public void MyMethod(T value) because the generic argument is at the class level.