Question

The documentation for the XmlSerializer.Serialize method states the following:

The XmlSerializer cannot serialize the following: arrays of ArrayList and arrays of List<T>.

However if I try with the following code it works (I am use List<int> and ArrayList). So is this a documentation defect, a new feature in .NET 4.5 that hasn’t made it’s way to documentation?

I had suspected that it could be an abbreviated message about how you cannot serialise a List<T> unless you have all the types in object graph, but that doesn’t make sense for ArrayList which is just object.

private static string Serialise<T>(T o)
{
    var serializer = new XmlSerializer(typeof(T));
    var memoryStream = new MemoryStream();
    serializer.Serialize(memoryStream, o);
    memoryStream.Position = 0;
    using (var reader = new StreamReader(memoryStream))
    {
        return reader.ReadToEnd();
    }
}

Answer 1

Read the documentation again – it says you can’t serialize arrays of List<T> or ArrayList (i.e. List<T>[] and ArrayList[]).

Sure enough, these work:

Serialise(new ArrayList());
Serialise(new List<int>());

These do not:

Serialise(new ArrayList[]{});
Serialise(new List<int>[]{});

The latter throw this exception:

System.InvalidOperationException: Unable to generate a temporary class (result=1).