Question

I’m trying to serialize an object as XML and have been using a little tester to experiment with different object behaviors when serializing as XML. I know binary serializers are deep and that XML is shallow. However, it does seem that it tries to serialize a List composed within another object when using XML.

My issue is that I get copied data when I serialize a List. Code and output follow:

class Program
{
    static void Main(string[] args)
    {
        TestSerializer original = new TestSerializer();
        System.Xml.Serialization.XmlSerializer x = new System.Xml.Serialization.XmlSerializer(original.GetType());
        x.Serialize(Console.Out, original);
        Console.WriteLine("\n\n\n");

        using (MemoryStream stream = new MemoryStream())
        {
            x.Serialize(stream, original);
            stream.Seek(0, SeekOrigin.Begin);

            TestSerializer copy = x.Deserialize(stream) as TestSerializer;
            x.Serialize(Console.Out, copy);
        }
        Console.ReadLine();
    }
}

public class TestSerializer
{
    public List<string> words = new List<string>();
    public TestSerializer()
    {
        words.Add("word");
        words.Add("anotherword");
    }
}

And the corresponding output:

<?xml version="1.0" encoding="IBM437"?>
<TestSerializer xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd=
"http://www.w3.org/2001/XMLSchema">
  <words>
    <string>word</string>
    <string>anotherword</string>
  </words>
</TestSerializer>



<?xml version="1.0" encoding="IBM437"?>
<TestSerializer xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd=
"http://www.w3.org/2001/XMLSchema">
  <words>
    <string>word</string>
    <string>anotherword</string>
    <string>word</string>
    <string>anotherword</string>
  </words>
</TestSerializer>

As you can see, the list content is doubled up when “original” is serialized, then deserialized to “copy”. Is there something I am missing as far this is concerned? It seems like there should not be duplicated data.

Answer 1

Put a breakpoint on the constructor of TestSerializer class. You will notice that it is called e.g. on the following line:

TestSerializer copy = x.Deserialize(stream) as TestSerializer;

So when you deserialize the object following happens

1. First instance of TestSerializer is created (populates the two values in the list) and it executes the default constructor
2. Dezerialization adds the items from the stream to the created object (now you have 4 items)