using System;

public class Program

{

    public static void Main()

    {

        var derived = new Derived();

        derived.Raise();

    }

}

​

public abstract class Base

{

    public event EventHandler Foo;

    public void Raise() => this.Foo?.Invoke(this, EventArgs.Empty);

}

​

public class Derived : Base

{

    public Derived()

    {

        this.Foo += (o, e) => Console.WriteLine("Foo called");  

    }

}