How to get generic argument types of generic type from derived type in c#

Question

Supose i have:

class MyBase<T1, T2>{}

class MyConcreteBase<T2> : MyBase<ConcreteType1, T2>{}

class MyConcrete1 : MyConcreteBase<ConcreteType2>{}

class MyConcrete2 : MyBase<ConcreteType1, ConcreteType2>{}

How do i get types of T1 and T2 if i have instance of MyConcrete1 or MyConcrete2 or MyConcreteBase or any other instance of type derived from MyBase<T1, T2>

The way i do it now is i'm "getting up" by inheritance chain using .GetType().BaseType while BaseType.Name.StartsWith("MyBase") and then using .GetGenericArguments()

It is working, but i'm not satisfied with it, especially .StartsWith("MyBase") part.

Anyone have other suggestions?

Answer 1

You can walk up the inheritance hierarchy and look for a GenericType, which is constructed from BaseType<,>. Try:

var type = c.GetType();
Type baseType = type;
while(null != (baseType = baseType.BaseType)) 
{
    if (baseType.IsGenericType) 
    {
        var generic = baseType.GetGenericTypeDefinition();
        if (generic == typeof(MyBase<,>)) 
        {
            var genericTypes = baseType.GetGenericArguments();
            // genericTypes has the type argument used to construct baseType.
            break;
        }
    }
}   

Answer 2

Yeah, don't use string parsing. You can simply use BaseType.IsAssignableFrom(typeof(MyBase<,>)) (might have to reverse the BaseType and MyBase<,> -- I always get that confused).

It might also be easier to expose the types as properties in your base class, e.g.:

public Type T1_Type { get { return typeof(T1); } }
public Type T2_Type { get { return typeof(T2); } }

I do have to ask, why do you need to extract these type parameters? This is a code smell to me.

EDIT: I should add that you can't use IsAssignableFrom as is for generics. Check out this answer for a full solution: How To Detect If Type is Another Generic Type