Why does the OnDeserialization not fire for XML Deserialization?

Question

I have a problem which I have been bashing my head against for the better part of three hours. I am almost certain that I've missed something blindingly obvious...

I have a simple XML file:

<?xml version="1.0" encoding="utf-8"?>
<WeightStore xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xmlns:xsd="http://www.w3.org/2001/XMLSchema">  
  <Records>
    <Record actual="150" date="2010-05-01T00:00:00" />
    <Record actual="155" date="2010-05-02T00:00:00" />
  </Records>
</WeightStore>

I have a simple class structure:

[Serializable]
public class Record
{
    [XmlAttribute("actual")] public double weight { get; set; }
    [XmlAttribute("date")]   public DateTime date { get; set; }
    [XmlIgnore]              public double trend { get; set; }
}

[Serializable]
[XmlRoot("WeightStore")]
public class SimpleWeightStore
{
    [XmlArrayAttribute("Records")]
    private List<Record> records = new List<Record>();
    public List<Record> Records { get { return records; } }

    [OnDeserialized()]
    public void OnDeserialized_Method(StreamingContext context)
    {
        // This code never gets called
        Console.WriteLine("OnDeserialized");
    }
}

I am using these in both calling code and in the class files:

using System.Xml.Serialization;
using System.Runtime.Serialization;

I have some calling code:

SimpleWeightStore weight_store_reload = new SimpleWeightStore();
TextReader reader = new StringReader(xml);
XmlSerializer deserializer = new XmlSerializer(weight_store.GetType());
weight_store_reload = (SimpleWeightStore)deserializer.Deserialize(reader);

The problem is that I am expecting OnDeserialized_Method to get called, and it isn't.

I suspect it might have something to do with the fact that it's XML deserialization rather than Runtime deserialization, and perhaps I am using the wrong attribute name, but I can't find out what it might be.

Any ideas, folks?

Solution 1

There's no equivalent of OnDeserialized for XML deserialization.

See this post for workarounds: How do you find out when you've been loaded via XML Serialization?

Solution 2

The only way you could do that in a graceful way is to manually implement IXmlSerializable, which is not fun. Simply; XmlSerializer doesn't support serialization callbacks.

Sometimes, though, you can switch to DataContractSerializer, which still offers xml capabilities but which does support serialization callbacks. Unfortunately the xml options are limited - it won't work for you xml structure, since that uses attributes (DataContractSerializer only supports elements).

You might also look at the comments on this answer, which discusses the points from this.

Comments

[Jonathan]

Darn. That's very annoying. Oh well. I have added a workaround involving a field which gets unset when I deserialize, and set again when the internal state is good.