C# interface inheritance

Question

Given:

public interface IA
{
    void TestMethod();
}

public interface IB : IA
{
}

Why:

typeof(IB).GetMethods().Count() == 0;

?

Just to be clear:

public class A
{
    public void TestMethod()
    {
    }
}

public class B : A
{
}

typeof(B).GetMethods().Count();

does work (it returns 5);

As a bonus:

typeof(IB).BaseType == null

Answer 1

You have to define some Bindingflags into GetMethods().

Try

typeof(IB).GetMethods(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.FlattenHierarchy).Count();

Answer 2

This seems to be the design of the GetMethods function. It doesn't support inherited members in interfaces. If you want to discover all the methods, you need to query each interface type directly.

Check out the community content section of this MSDN article.

Answer 3

Here is the code for getting the counts for both IA and IB:

var ibCount = typeof(IB).GetMethods().Count(); // returns 0
var iaCount = typeof (IB).GetInterfaces()[0].GetMethods().Count(); // return 1

Note that in production code I wouldn't use GetInterfaces()[0] as typically in the code where I would use this I can't assume that I will always have at least one interface.

I also tried out the bindingflags as follows:

const BindingFlags bindingFlags = BindingFlags.Public | BindingFlags.Instance | BindingFlags.FlattenHierarchy;
var ibCount = typeof(IB).GetMethods(bindingFlags).Count();

However, this will still return 0 as interface IB still doesn't implement method TestMethod(). Interface IA does. Using binding flags would work if both IA and IB were classes. In that case however, you get a return value of 5. Don't forget that IA implicitly derives from class Object!

Answer 4

Consider IA to be an interface of IB, not its base.