反射：通用列表的非通用子类中包含的项类型

Question

public class MyList : List<MyClass>

How can I get the type MyClass through reflection if I have an object that contains an instance of MyList ? The list can be empty, so I can't do something like myList[0].GetType() .

ps I can't just stop using MyList and directly use the generic List instead (the situation is a bit more complicated, and there are reasons for "hiding" the generic argument), so I can't pick up MyClass through GetGenericArguments() .

Answer 1

var elementType = (
    from iface in myList.GetType().GetInterfaces()
    where iface.IsGenericType
    where iface.GetGenericTypeDefinition() == typeof(IList<>)
    select iface.GetGenericArguments()[0])
        .Single();

I use IList<T> instead of list. This is more generic. However, there is also the change of a type implementing multiple ILis<T> versions (such as IList<string> and IList<int> ).

Answer 2

You can get the base type, which will be List<MyClass> ; from it you can get the generic type argument with GetGenericArguments .

Answer 3

MyList list = new MyList();
Type baseTypeGenericArgument = list.GetType().BaseType.GetGenericArguments()[0];
string argumentTypeName = baseTypeGenericArgument.GetType().FullName;

Answer 4

Is your class implements generic interfaces? you can use the following code:

Type argument = GetGenericArgument(typeof(MyList), typeof(IList<>));
//...
static Type GetGenericArgument(Type type, Type genericTypeDefinition) {
    Type[] interfaces = type.GetInterfaces();
    for(int i = 0; i < interfaces.Length; i++) {
        if(!interfaces[i].IsGenericType) continue;
        if(interfaces[i].GetGenericTypeDefinition() == genericTypeDefinition)
            return interfaces[i].GetGenericArguments()[0];
    }
    return null;
}

Without interfaces you can try the following:

class A { }
class B { }
class G<T> { }
class G1<T> : G<A> { }
class G2 : G1<B> { }
//...
Type argument1 = GetGenericArgument(typeof(G2)); // B
Type argument2 = GetGenericArgument(typeof(G2),1 ); // A
//...
static Type GetGenericArgument(Type type, int level = 0) {
    do {
        if(type.IsGenericType && 0 == level--)
            return type.GetGenericArguments()[0];
        type = type.BaseType;
    }
    while(type != null);
    return null;
}