Question

I have a marker interface defined as

public interface IExtender<T> { } 

I have a class that implements IExtender

public class UserExtender : IExtender<User> 

At runtime I recieve the UserExtender type as a parameter to my evaluating method

public Type Evaluate(Type type) // type == typeof(UserExtender) 

How do I make my Evaluate method return

typeof(User) 

based on the runtime evaluation. I am sure reflection is involved but I can’t seem to crack it.

(I was unsure how to word this question. I hope it is clear enough.)

Answer 1

I went this way based on some of the tidbits provided. It could be made more robust to handle multiple generic arguments on the interface…. but I didn’t need it to 😉

private static Type SafeGetSingleGenericParameter(Type type, Type interfaceType) {     if (!interfaceType.IsGenericType || interfaceType.GetGenericArguments().Count() != 1)         return type;      foreach (Type baseInterface in type.GetInterfaces())     {         if (baseInterface.IsGenericType &&                 baseInterface.GetGenericTypeDefinition() == interfaceType.GetGenericTypeDefinition())         {             return baseInterface.GetGenericArguments().Single();         }     }      return type; }