如何从 c# 中的派生类型获取泛型类型的泛型参数类型

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, eg:

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

Answer 3

Would be good if you would tell us a bit more about what you want to achive. Guessing what you idea is, I would say: Just walk the complete inheritance chain as long as BaseType is not null . And then check for each type if it's generic and if yes, call GetGenericArguments . Should be a matter of a few predicates and one or two LINQ expressions.

Answer 4

I can't think of anything clever, so I'd probably just do this:

class MyBase<T1, T2> {
    protected Type GetT1() { return typeof(T1); }
    protected Type GetT2() { return typeof(T2); }
}

Answer 5

Here is a function that will accept any type (assuming it has a base class with generic parameters) and return the types of that instance's base class's generic parameters:

public Type[] BaseGenericTypes<T>(T instance)
    {
        Type instanceType = instance.GetType();

        Type objectType = new object().GetType();

        while (instanceType.BaseType != objectType)
        {
            instanceType = instanceType.BaseType;
        }
        return instanceType.GetGenericArguments();
    }

The nice thing about this method is you don't need to know anything about the base class or any of its subsequent derived classes.

Answer 6

Do you mean: Type.GetGenericArguments Method ?