getting type T from IEnumerable<T>

Question

hi, is there a way to retrieve type T from IEnumerable<T> through reflection?

e.g.

i have a variable IEnumerable<Child> info; i want to retrieve Child's type through reflection

Answer 1

IEnumerable<T> myEnumerable;
Type type = myEnumerable.GetType().GetGenericArguments()[0];

Thusly,

IEnumerable<string> strings = new List<string>();
Console.WriteLine(strings.GetType().GetGenericArguments()[0]);

prints System.String.

See MSDN for Type.GetGenericArguments.

Edit: I believe this will address the concerns in the comments:

// returns an enumeration of T where o : IEnumerable<T>
public IEnumerable<Type> GetGenericIEnumerables(object o) {
    return o.GetType()
            .GetInterfaces()
            .Where(t => t.IsGenericType == true
                && t.GetGenericTypeDefinition() == typeof(IEnumerable<>))
            .Select(t => t.GetGenericArguments()[0]);
}

Some objects implement more than one generic IEnumerable so it is necessary to return an enumeration of them.

Answer 2

typeof(IEnumerable<Foo>).GetGenericArguments()[0] will return the first generic argument - in this case typeof(Foo).

Answer 3

Just use typeof(T)

EDIT: Or use .GetType().GetGenericParameter() on an instantiated object if you don't have T.

Answer 4

If you know the IEnumerable<T> (via generics), then just typeof(T) should work. Otherwise (for object, or the non-generic IEnumerable), check the interfaces implemented:

        object obj = new string[] { "abc", "def" };
        Type type = null;
        foreach (Type iType in obj.GetType().GetInterfaces())
        {
            if (iType.IsGenericType && iType.GetGenericTypeDefinition()
                == typeof(IEnumerable<>))
            {
                type = iType.GetGenericArguments()[0];
                break;
            }
        }
        if (type != null) Console.WriteLine(type);

Answer 5

Thank you very much for the discussion. I used it as a basis for the solution below, which works well for all cases that are of interest to me (IEnumerable, derived classes, etc). Thought I should share here in case anyone needs it also:

  Type GetItemType(object someCollection)
  {
    var type = someCollection.GetType();
    var ienum = type.GetInterface(typeof(IEnumerable<>).Name);
    return ienum != null
      ? ienum.GetGenericArguments()[0]
      : null;
  }