C# XML serialization of derived classes

[XmlInclude(typeof(Square))]public abstract class Shape {...}

(repeat for all known subtypes)

If the types are only known at runtime, you can supply them to the XmlSerializer constructor, but: then it is important to cache and reuse that serializer instance; otherwise you will haemorrhage dynamically created assemblies. It does this automatically when you use the constructor that just takes a Type, but not for the other overloads.

Solution:

class Program    {        static void Main(string[] args)        {            Shape[] a = new Shape[2] { new Square(1), new Triangle() };            FileStream fS = new FileStream("C:\\shape.xml",FileMode.OpenOrCreate);            //this could be much cleaner            Type[] t = { a[1].GetType(), a[0].GetType() };            XmlSerializer xS = new XmlSerializer(a.GetType(),t);            Console.WriteLine("writing");            try            {                xS.Serialize(fS, a);            }            catch (Exception e)            {                Console.WriteLine(e.InnerException.ToString());                Console.ReadKey();            }            fS.Close();            Console.WriteLine("Fin");        }    }namespace XMLInheritTests{    [XmlInclude(typeof(Square))]    [XmlInclude(typeof(Triangle))]    public abstract class Shape    {        public Shape() { }        public int area;        public int edges;    }}

Thanks; I no doubt will have another problem very soon :S

You can use XmlArrayItem to get around this:

public class XMLFile{    [XmlArray("MasterFiles")]    [XmlArrayItem("Supplier", typeof(Supplier))]    [XmlArrayItem("Customer", typeof(Customer))]    public List<MasterElement> MasterFiles;}

From the linked MSDN:

The XmlArrayItemAttribute supports polymorphism--in other words, it allows the XmlSerializer to add derived objects to an array.