C# - Get the item type for a generic list

You could use the Type.GetGenericArguments method for this purpose.

List<Foo> myList = ...

Type myListElementType = myList.GetType().GetGenericArguments().Single();

For a more robust approach:

public static Type GetListType(object someList)
{
    if (someList == null)
        throw new ArgumentNullException("someList");

    var type = someList.GetType();

    if (!type.IsGenericType || type.GetGenericTypeDefinition() != typeof(List<>))
        throw new ArgumentException("Type must be List<>, but was " + type.FullName, "someList");

    return type.GetGenericArguments()[0];
}

But if your variable is typed List<T> then you can just use typeof(T). For example:

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

Note that you don't really even need the someList parameter. This method is just an example for how you could use typeof if you are already in a generic method. You only need to use the reflection approach if you don't have access to the T token (the list is stored in a non-generic-typed variable, such as one typed IList, object, etc.).

list.GetType().GetGenericArguments()[0]