How detect is a method in a C# class is implementing a method from an interface?

Question

I want to be able to use reflection to tell that an implementation of the method GetName in SomClassImpl comes from the interface IHasName . As an example:

public interface IHasName
{
    string GetName();
}

public interface IOtherInterface
{
    //...elided...
}

public class MyClass : IHasName, IOtherInterface
{
    /*
     * I want to use reflection to know this 
     * implements IHasName.GetName()
     */
    public string GetName()
    {
        return "me";
    }
}

Is this possible?

When I tried typeof(MyClass).GetMethod("GetName").GetBaseDefinition().DeclaringType and typeof(MyClass).GetMethod("GetName").DeclaringType , they both return the implementing class, not the interface.

Answer 1

I see two possibilities your scenario to happen:

1. Class implements the interface
2. Class inherits a class which implements the interface

In the former case, typeof(Foo).GetMethod("GetName", BindingFlags.Public | BindingFlags.Instance | BindiFoongFlags.DeclaredOnly) returns the method info.

In the latter case, typeof(Bar).GetMethod("GetName", BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly) returns null .

See an example here .

Answer 2

The following will tell if the object implements the interface:

unkObj is IHasName

This will too if using reflection on a type instead of an object:

typeof(IHasName).IsAssignableFrom(typeof(MyClass))

This will get the method associated with the interface, and invoking it with any type that implements the interface with call the associated method in its class:

MethodInfo methodIHasName = typeof(IHasName).GetMethod("GetName", BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly)
string name = methodIHasName.Invoke(unkObj, new object[0]);

If you absolutely need to get the MethodInfo of MyClass and all you have is the MethodInfo of the interface IHasName , you can map the interface as follows: (Thanks @Alexei Levenkov for the link)

var map = typeof(MyClass).GetInterfaceMap(methodIHasName.DeclaringType);
var index = Array.IndexOf(map.InterfaceMethods, methodIHasName);
return map.TargetMethods[index];