How to get MethodInfo of interface method, having implementing MethodInfo of class method?

Question

I have a MethodInfo of an interface method and Type of a class that implements the interface. I want to find the MethodInfo of the class method that implements the interface method.

The simple method.GetBaseDefinition() does not work with interface methods. Lookup by name won't work either, because when implementing interface method explicitly it can have any name (yes, not in C#).

So what is the correct way of doing that that covers all the possibilities?

Answer 1

OK, I found a way, using GetInterfaceMap.

var map = targetType.GetInterfaceMap(interfaceMethod.DeclaringType);
var index = Array.IndexOf(map.InterfaceMethods, interfaceMethod);

if (index == -1)
{
    //this should literally be impossible
}

return map.TargetMethods[index];

Answer 2

Hmmm - not sure about the correct way, but you can do it by looping through all the interfaces on your type, and then searching the interfaces for the method. Not sure if you can do it directly without the looping through the interfaces, as you're kinda stuck without GetBaseDefinition().

For my interface with a single method (MyMethod) and my type (MyClass) which implements this method I can use this:

MethodInfo interfaceMethodInfo = typeof(IMyInterface).GetMethod("MyMethod");
MethodInfo classMethodInfo = null;
Type[] interfaces = typeof(MyClass).GetInterfaces();

foreach (Type iface in interfaces)
{
    MethodInfo[] methods = iface.GetMethods();

    foreach (MethodInfo method in methods)
    {
        if (method.Equals(interfaceMethodInfo))
        {
            classMethodInfo = method;
            break;
        }
    }
}

You'd have to check that the MethodInfo.Equals works if the two methods have different names. I didn't even know that was possible, probably cos I'm a C#'er