Question

I need the above feature because I can only store StringCollection to Settings, not List of strings.

How does one convert List into StringCollection?

Answer 1

How about:

StringCollection collection = new StringCollection();
collection.AddRange(list.ToArray());

Alternatively, avoiding the intermediate array (but possibly involving more reallocations):

StringCollection collection = new StringCollection();
foreach (string element in list)
{
    collection.Add(element);
}

Converting back is easy with LINQ:

List<string> list = collection.Cast<string>().ToList();