When a class is inherited from List<>, XmlSerializer doesn't serialize other attributes

21
votes

I'm having a situation here, I need my class to be inherited from List<ItemType>, but when I do this XmlSerializer does not serialize any property or field declared in my class, the following sample demonstrates:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        DoSerialize();
    }
    private void DoSerialize()
    {
        MyClass obj = new MyClass();
        obj.Add(1);
        obj.Add(2);
        obj.Add(3);
        XmlSerializer s = new XmlSerializer(typeof(MyClass));
        StringWriter sw = new StringWriter();
        s.Serialize(sw, obj);
    }
}
[Serializable]
[XmlRoot]
public class MyClass : List<int>
{
    public MyClass()
    {
    }
    int myAttribute = 2011;
    [XmlAttribute]
    public int MyAttribute
    {
        get
        {
            return myAttribute;
        }
        set
        {
            myAttribute = value;
        }
    }
}

the resulting XML:

<?xml version="1.0" encoding="utf-16"?>
<ArrayOfInt xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <int>1</int>
  <int>2</int>
  <int>3</int>
</ArrayOfInt>
2
c#.netlistxml-serializationienumerable
This is one of many reasons you generally shouldn't subclass List. – Kirk Woll
@kirk: Yeah, I think also the same, but this time I have to, I didn't start the project, it's like this and I have to do serialization on it – Esam Bustaty
@Kirk not disagreeing with that principle, but here (per the link in @driis answer) the problem is actually that implementing IEnumerable at all means your own properties don't get serialised! Which seems pretty harsh... – AakashM
possible duplicate of XmlSerializer doesn't serialize everything in my class – AakashM
@AakashM Sorry for the duplicate, I searched but didn't find it, perhaps I was using the wrong kewords – Esam Bustaty

2 Answers

25
votes

This is by design. I don't know why this decision was made, but it is stated in the documentation:

  • Classes that implement ICollection or IEnumerable. Only collections are serialized, not public properties.

(Look under "Items that can be serialized" section). Someone has filed a bug against this, but it won't be changed - here, Microsoft also confirms that not including the properties for classes implementing ICollection is in fact the behaviour of XmlSerializer.

A workaround would be to either:

  • Implement IXmlSerializable and control serialization yourself.

or

  • Change MyClass so it has a public property of type List (and don't subclass it).

or

  • Use DataContractSerializer, which handles this scenario.
6
votes

Here's a though for you to consider.

You can have a class that is a container class like this:

class ContainerObject
{
     public int MyNewProperty { get; set; }

     [XmlElement("")]
     public List<int> MyList { get; set; }
}

The trick is to have XmlElement name = "" above the List element.

When this is serialized into xml, you will have:

<ContainerObject>
   <MyNewProperty>...</MyNewProperty>

   <int>...</int>
   <int>...</int>

</ContainerObject>

If you like, you can also create another class for items in a list

 class MyItem
 {
     public int MyProperty {get;set;} 

 }

and then instead of having List of ints, have a List of MyItems.

This was you control XmlElement name of every item in a list.

I hope this was helpful.