Comments on Nostatic Software Dev Blog: C# Xml List Serialization Behavior

Hi Mike, Maybe related to this is the non-intuiti...

2010-04-01T09:23:04.446-07:00

Hi Mike,

Maybe related to this is the non-intuitive behaviour of serializing/deserializing List(List(T)). I write round brackets, the post doesn't seem to accept the angle brackets. If the "inner" List(T) is actually null, it is deserialized as a List(T)-object with Count=0. Which is also not "the correct behavior...

Regards,
Bart Donders
the Netherlands

Hey Mike, I stumbled onto your post and thought I&...

2009-10-16T17:41:26.935-07:00

Hey Mike, I stumbled onto your post and thought I'd shed a little more light on the matter.

My guess for the cause of this behavior has to do more with the guts of List(Of T); if you look at the list's Items() collection you'll see it's declared as a ReadOnly instance of IList(Of T).

The fact that it's ReadOnly says that it's not compatible with serialization, which works against public properties.

Then again, it's nothing I would have expected either--but at least it looks like there's a reason for the behavior.

Hi Pete - I understand "why" it happens, and that ...

2009-02-19T14:57:00.000-08:00

Hi Pete - I understand "why" it happens, and that it is not too difficult to work around, I just don't think it is the correct behavior. Default initialization of properties just should not interact with serialization in this manner.

It would be easy for Microsoft to fix. I've since rolled my own Xml serializer to work around this, and other issues/limitations with the way that .NET serialization works (the biggest one being the inability to serialize interfaces).

//
// Only a proof of concept.
//

sta...

2009-02-19T11:39:00.000-08:00

//
// Only a proof of concept.
//

static void Main(string[] args)
{
XmlTest xmlTest = new XmlTest();
xmlTest.setList();

// Outputs 3
Console.WriteLine(xmlTest.IntegerList.Count);

TextWriter writer = new StreamWriter("test.xml");
XmlSerializer serializer = new XmlSerializer(typeof(XmlTest));
serializer.Serialize(writer, xmlTest);
writer.Close();

FileStream fs = new FileStream("test.xml", FileMode.Open);
XmlReader reader = new XmlTextReader(fs);
xmlTest = (XmlTest)serializer.Deserialize(reader);
fs.Close();

// Outputs 3
Console.WriteLine(xmlTest.IntegerList.Count);
Console.ReadKey();
}

[Serializable]
public class XmlTest
{
public void setList(){ integerList = new List< int > { 1, 2, 3 };}

private List< int > integerList = null;

public List< int > IntegerList
{
get { return integerList; }
set { integerList = value; }
}
}

Mike,

The reason for the discrepancy is as ...

2009-02-19T11:36:00.000-08:00

Mike,

The reason for the discrepancy is as follows. Have a look at the integerList instance field; this is 'populated' upon instantiation. Your example then serializes to a .xml file (in this case test.xml) -- so far so good. Just before de-serialization {1,2,3} is already in the list because you've just used the "new" modifier. De-serialization occurs, and you're left with {1,2,3,1,2,3}.

Add something like:

public void setList(){ integerList = new List< int > { 1, 2, 3 };}

to the XMLTest class; call it just before you do your serialize.

Yeah, I'm usually too lazy to do that, though. Esp...

2007-12-05T13:16:00.000-08:00

Yeah, I'm usually too lazy to do that, though. Especially when I have lots of relatively simple objects.

Generally the XMLSerializer likes to deal with fie...

2007-12-03T16:04:00.000-08:00

Generally the XMLSerializer likes to deal with fields. I generally create pure data objects that I use for my serialization and facade those with the actual access objects. That means I also can control the public interface of my objects, since XMLSerialization insists on having everything public (unlike the binary formatter).