using static System.Console;

using System;

using System.Reflection;

​

public class Program {

    public static void Main(string[] args) {

        var x = new Derived();

        x.Method();

    }

}

​

[AttributeUsage(AttributeTargets.All)]

public class MyAttribute : Attribute {

    public MyAttribute() => WriteLine("Executei o atributo...");

}

​

​

class Base {

    public Base() { 

        foreach (var method in this.GetType().GetMethods(BindingFlags.Public | BindingFlags.Instance)) method.GetCustomAttributes(true);

    }

}

​

class Derived : Base {

    public Derived() => WriteLine("Executei o construtor da classe...");

    [My]

    public void Method() => WriteLine("Executei o método...");

}