Mix .Net Xml Serialization and custom xml serialization

Question

Is it possible to mix the .net framework serialization in xml with some handmade serialization method ?

I have a "sealed" class Outline which contains a method WriteToXml() that I would like to use.

More difficult, I have another class which contains :

class Difficult
{

    [XmlElement("Point", typeof(Point))]
    [XmlElement("Contour", typeof(Outline))]
    [XmlElement("Curve", typeof(Curve))]
    public object Item;
}

It corresponds to a xsi:choice.

Curve and Point should be serialized using the standard method, and I would like to tell the serializer to use WriteToXml() when Item is an Outline .

Answer 1

If Point, Outline, and Curve all share a common base class other than object, you could use a custom SerializationWrapper. Try this:

public class DrawnElement {}
public class Point : DrawnElement {}
public class Curve : DrawnElement {}
public class Outline : DrawnElement
{
    public string WriteToXml()
    {
        // I assume that you have an implementation already for this
        throw new NotImplementedException();
    }
}

public class Difficult
{
    [XmlElement(typeof(DrawnElementSerializationWrapper))]
    public DrawnElement Item;
}

public class DrawnElementSerializationWrapper : IXmlSerializable
{

    private DrawnElement item;

    public DrawnElementSerializationWrapper(DrawnElement item) { this.item = item; }

    public static implicit operator DrawnElementSerializationWrapper(DrawnElement item) { return item != null ? new DrawnElementSerializationWrapper(item) : null; }

    public static implicit operator DrawnElement(DrawnElementSerializationWrapper wrapper) { return wrapper != null ? wrapper.item : null; }

    public System.Xml.Schema.XmlSchema GetSchema()  { return null; }

    public void ReadXml(System.Xml.XmlReader reader)
    {
        // read is not supported unless you also output type information into the xml
    }

    public void WriteXml(System.Xml.XmlWriter writer)
    {
        var itemType = this.item.GetType();

        if (itemType == typeof(Outline))    writer.WriteString(((Outline) this.item).WriteToXml());
        else                                new XmlSerializer(itemType).Serialize(writer, this.item);
    }

}