public void WriteXml(XmlWriter writer) { Dius_Wrapper dw = new Dius_Wrapper() { collection = new SortedSet <Yem>(this), a = this.a, d = this.d }; List <Type> knownTypes = new List <Type>() { typeof(Dius) }; DataContractSerializer ser = new DataContractSerializer(dw.GetType(), knownTypes); ser.WriteObject(writer, dw); }