Question

I’m writing a Windows Store App and I need to store some data in Roaming Storage; for that I needed to serialize/deserialize some data. My serializer/deserializer functions are as below:

public string Serialize()
    {
        try
        {
            StringWriter sw = new StringWriter();

            XmlSerializer xs = new XmlSerializer(typeof(RssData));
            xs.Serialize(sw, this);


            return sw.ToString();
        }
        catch (Exception ex)
        {
            System.Diagnostics.Debug.WriteLine(ex);
            return String.Empty;
        }
    }

    public void Deserialize(string serialized)
    {
        try
        {
            XmlSerializer xs = new XmlSerializer(typeof(RssData));
            XmlReader xr = XmlReader.Create(new StringReader(serialized));
            RssData rd = xs.Deserialize(xr) as RssData;
            this.categoryList = rd.categoryList;
            this.defaultCategory = rd.defaultCategory;
        }
        catch(Exception ex)
        {
            System.Diagnostics.Debug.WriteLine(ex);
        }
    }

In summary, RssData has a list of RssCategory, and each RssCategory has a RssFeed. There is no problem with serialization and the following string is an example that I’ve produced using the Serialize function above:

<?xml version="1.0" encoding="utf-16"?>
<RssData xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <CategoryList>
    <RssCategory>
      <Name>No Category</Name>
      <RssList>
        <RssFeed>
          <Title>HABERTURK.COM</Title>
          <Url>http://www.haberturk.com/rss</Url>
          <Image>http://www.haberturk.com/images/htklogo2.jpg</Image>
          <Subtitle>HABERTÜRK - Türkiye'nin En Büyük İnternet Gazetesi</Subtitle>
        </RssFeed>
      </RssList>
    </RssCategory>
  </CategoryList>
</RssData>

However, when I Deserialize this XML, the resulting RssData has a CategoryList with 2 RssCategories, one is a RssCategory named “No Category” with an empty RssList, the other one is the correct one as defined in the XML; i.e. “No Category” with one RssFeed.

Is it a problem with my code or is XmlSerializer bugged?

Answer 1

Ok it seems that XmlSerializer first constructs the object using its no-parameter constructor then adds each item in the XML to the appropriate list. Thus if the constructor adds some items to that list, deserializing will result in a list that includes any item added in the constructor.

Edit: So if you serialize/deserialize a class that has a property of type Array/List/Container etc, in the no-parameter constructor you have to initialize it, but do not add anything to it.