using System;

using System.Linq;

using System.Reflection;

​

public class Program

{

    [AttributeUsage(AttributeTargets.Class, AllowMultiple = true, Inherited = true)]

    public abstract class TestAttributeBase : Attribute

    {

    }

    public class TestAttribute : TestAttributeBase

    {

        public string Value {get; private set;}

        public TestAttribute(string value)

        {

            Value = Value;  

        }

    }

    [TestAttribute("A")]

    public class A {

    }

    [TestAttribute("B")]

    [TestAttribute("C")]

    public class B : A

    {

    }

    public static void Main()

    {

        var b = new B();

        var customAttributes = typeof(B).GetCustomAttributes<TestAttribute>(true).ToList();

        Console.WriteLine(customAttributes.Count);

    }

}