Question

When reflecting on an interface type, I only get the members of the specific type, not inherited members.

In this over-simplified example, the program only prints “Name”, not “ItemNumber”, “Name” as I would expect:

using System;

public interface IBasicItem
{
    string ItemNumber { get; set; }
}

public interface IItem : IBasicItem
{
    string Name { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        var type = typeof (IItem);
        foreach (var prop in type.GetProperties())
            Console.WriteLine(prop.Name);
    }
}

What is the rationale behind this ? When I am inheriting from the base interface, I am saying that any of the implementations of my interface, must also implement the inherited members. In other words, IItem is-a IBasicItem. So why does the inherited member not show up using reflection ?

Answer 1

I think this is exactly what Phil Haack just blogged about.

From the ECMA-335 Common Language Infrastructure specification:

8.9.11 Interface type derivation Interface types can require the
implementation of one or more other
interfaces. Any type that implements
support for an interface type shall
also implement support for any
required interfaces specified by that
interface. This is different from
object type inheritance in two ways:

• Object types form a single inheritance tree; interface types do
  not.
• Object type inheritance specifies how implementations are inherited;
  required interfaces do not, since
  interfaces do not define
  implementation. Required interfaces
  specify additional contracts that an
  implementing object type shall
  support.

To highlight the last
difference, consider an interface,
IFoo, that has a single method. An
interface, IBar, which derives from
it, is requiring that any object type
that supports IBar also support IFoo.
It does not say anything about which
methods IBar itself will have.

Referenced from:
http://haacked.com/archive/2009/11/10/interface-inheritance-esoterica.aspx