Append an object to an IEnumerable<> via reflection

Question

Hi,

I need to be able to access a property via reflection, and, knowing that this property is an IEnumerable, append an object to it.

Something like this:

Object o;
MemberInfo m;

Array arr; // Except use IEnumerable, may have to take account of value/ref types
arr = (Array)((PropertyInfo)m).GetValue(o, null); }

List<o.GetType()> newArr = new List<o.GetType()>(); /* fails */
newArr.AddRange(arr);
newArr.Add(o);

((PropertyInfo)m).SetValue(o, newArr.ToArray(), null);

Can you help me where I'm going wrong :-)

Solution:

See accepted answer comments. Also (http://stackoverflow.com/questions/1371347/get-the-actual-type-of-a-generic-object-parameter/1371378#1371378) is of help.

Answer 1

It sounds like you're essentially asking how to make a List<T> based on an unknown-at-compile-time type. For this you'll have to use a bit more reflection magic:

Type genericListType = typeof(List<>);
Type listType = genericListType.MakeGenericType(o.GetType());
object listInstance = Activator.CreateInstance(listType);

That would create a List<T> out of a runtime type.

But really, your code would be much simpler if you simply use ArrayList:

ArrayList list = new ArrayList(arr);
list.Add(o);
Array newArray = list.ToArray(o.GetType());

Answer 2

Once you have an IEnumerable type, use something like this to append to it:

public static IEnumerable<T> Append<T>(this IEnumerable<T> original, T next)
{
    foreach (T item in original) yield return item;
    yield return next;
}

public static IEnumerable<T> Append<T>(this IEnumerable<T> original, params T[] next)
{
    foreach (T item in original) yield return item;
    foreach (T item in next) yield return item;
}

public static IEnumerable<T> Append<T>(this IEnumerable<T> original, IEnumerable<T> next)
{
    foreach (T item in original) yield return item;
    foreach (T item in next) yield return item;
}