huh? in IgnoreDataMemberAttribute

http://msdn.microsoft.com/en-us/library/system.runtime.serialization.datamemberattribute.aspx

The data contract model is an "opt-in" model. Applying the DataMemberAttribute to a field or property explicitly specifies that the member value will be serialized. In contrast, the BinaryFormatter serializes public and private fields of a type, and the XmlSerializer serializes only public fields and properties of a type. （下線筆者）

http://msdn.microsoft.com/en-us/library/system.runtime.serialization.ignoredatamemberattribute.aspx

Apply the IgnoreDataMemberAttribute attribute to opt-out of the default DataContractSerializer behavior. By default, the DataContractSerializer serializes all publicly visible types. All public read/write properties and fields of the type are serialized. You can change the default behavior by applying the DataContractAttribute and DataMemberAttribute attributes to the types and members. （下線筆者）

（ ﾟдﾟ）ﾎﾟｶｰﾝ

…いや、どう見ても前者が正しいです。本当にありがとうございました。

using System;

using System.IO;

using System.Runtime.Serialization;

using System.Xml;
[DataContract]

public class Wrapper

{

  [DataMember (Order = 1)]

  public Test T;
  [DataMember (Order = 2)]

  public Test T2;

}
[DataContract]

public class Test

{

  [DataMember]

  public string F = "x";
  public static void Main ()

  {

    string ns = "http://schemas.microsoft.com/2003/10/Serialization/";

    var dc = new DataContractSerializer (typeof (Wrapper));

    Test t = new Test ();

    using (var xw = XmlWriter.Create (Console.Out)) {

      xw.WriteStartElement ("z", "root", ns);

      dc.WriteObject (xw, new Wrapper () {T = t, T2 = t});

      xw.WriteEndElement ();

    }

  }

}

<?xml version="1.0" encoding="shift_jis"?><z:root xmlns:z="http://schemas.microsoft.com/2003/10/Serialization/"><Wrapper xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.datacontract.org/2004/07/"><T><F>x</T><T2><F>x</F></T2></Wrapper></z:root>