using System;

​

public class Program

{

    public static void Main()

    {

        var derived = new Derived();

        derived.Raise();

    }

}

​

public abstract class Base

{

    public event EventHandler Foo;

    public Base()

    {

        Foo += OnFooBase;

    }

    private void OnFooBase(object sender, EventArgs e)

    {

        Console.WriteLine("OnFooBase called");

    }

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

}

​

public class Derived : Base

{

    public Derived()

    {

        Foo += OnFooDerived;

    }

    private void OnFooDerived(object sender, EventArgs e)

    {

        Console.WriteLine("OnFooDerived called");

    }

}