DataContractSerializer, KnownType and inheritance

Question

I've read many articles about known types and i belive my example should work. But it doesn't. I'm getting the following exception on deserialization and don't understand why:

Error in line 1 position 2. Expecting element 'A' from namespace 'http://schemas.datacontract.org/2004/07/ConsoleApplication2'.. Encountered 'Element' with name 'C', namespace 'http://schemas.datacontract.org/2004/07/ConsoleApplication2'.

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

namespace ConsoleApplication2
{
    [DataContract][KnownType(typeof(C))]class A { }
    [DataContract]class C : A { }

    class Program
    {
     static void Main(string[] args)
     {
      A a = new C();
      string data;

      var serializer = new DataContractSerializer(a.GetType());
      using (var sw = new StringWriter())
      {
       using (var xw = new XmlTextWriter(sw))
        serializer.WriteObject(xw, a);
       data = sw.ToString();
      }

      serializer = new DataContractSerializer(typeof(A));
      using (var sr = new StringReader(data))
      using (var xr = new XmlTextReader(sr))
       a = (A)serializer.ReadObject(xr);
     }
    }
}

What am i missing?

Answer 1

Change the way you create serializer:

var serializer = new DataContractSerializer(typeof(A));

istead of a.GetType();

It works. Xml that is generated is different - was sth like this:

<C> ...

and now is:

<A i:type="C"> ...