How to get the type of T from a member of a generi

Question

Let say I have a generic member in a class or method, so:

public class Foo<T>
{
    public List<T> Bar { get; set; }

    public void Baz()
    {
        // get type of T
    }   
}

When I instantiate the class, the T becomes MyTypeObject1, so the class has a generic list property: List<MyTypeObject1>. The same applies to a generic method in a non-generic class:

public class Foo
{
    public void Bar<T>()
    {
        var baz = new List<T>();

        // get type of T
    }
}

I would like to know, what type of objects the list of my class contains. So the list property called Bar or the local variable baz, contains what type of T?

I cannot do Bar[0].GetType(), because the list might contain zero elements. How can I do it?

Answer 1

(note: I'm assuming that all you know is object or IList or similar, and that the list could be any type at runtime)

If you know it is a List<T>, then:

Type type = abc.GetType().GetGenericArguments()[0];

Another option is to look at the indexer:

Type type = abc.GetType().GetProperty("Item").PropertyType;

Using new TypeInfo:

using System.Reflection;
// ...
var type = abc.GetType().GetTypeInfo().GenericTypeArguments[0];

Answer 2

Type:

type = list.AsEnumerable().SingleOrDefault().GetType();

Answer 3

If I understand correctly, your list has the same type parameter as the container class itself. If this is the case, then:

Type typeParameterType = typeof(T);

If you are in the lucky situation of having object as a type parameter, see Marc's answer.

Answer 4

With the following extension method you can get away without reflection:

public static Type GetListType<T>(this List<T> _)
{
    return typeof(T);
}

Or more general:

public static Type GetEnumeratedType<T>(this IEnumerable<T> _)
{
    return typeof(T);
}

Usage:

List<string>        list    = new List<string> { "a", "b", "c" };
IEnumerable<string> strings = list;
IEnumerable<object> objects = list;

Type listType    = list.GetListType();           // string
Type stringsType = strings.GetEnumeratedType();  // string
Type objectsType = objects.GetEnumeratedType();  // BEWARE: object

Answer 5

The GetGenericArgument() method has to be set on the Base Type of your instance (whose class is a generic class myClass<T>). Otherwise, it returns a type[0]

Example:

Myclass<T> instance = new Myclass<T>();
Type[] listTypes = typeof(instance).BaseType.GetGenericArguments();

Answer 6

Try

list.GetType().GetGenericArguments()