如何让XMLSerializer将命名空间添加到嵌套对象中的属性？(How do I get the XMLSerializer to add namespaces to attributes in nested objects?)

 这是我得到的： 
 
<ex:test soap:mustUnderstand="1" xmlns:ex="http://www.example.com/namespace">
  <ex:A Type="lorem">ipsum</ex:A>
</ex:test>
 
 这是我想要的：（请注意，Type-attribute前缀为ex。） 
 
<ex:test soap:mustUnderstand="1" xmlns:ex="http://www.example.com/namespace">
  <ex:A ex:Type="lorem">ipsum</ex:A>
</ex:test>
 
 这是我的代码： 
 
  [XmlType(Namespace = "http://www.example.com/namespace")]
  [XmlRoot("ex", Namespace = "http://www.example.com/namespace")]
  public class TestSoapHeader : SoapHeader {
    private TestSoapHeaderTypeValuePair _a;

    public TestHeader() {
      MustUnderstand = true;
    }

    [XmlNamespaceDeclarations]
    public XmlSerializerNamespaces xmlsn {
      get {
        XmlSerializerNamespaces xsn = new XmlSerializerNamespaces();
        xsn.Add("ex", "http://www.example.com/namespace");
        return xsn;
      }
      set { }
    }

    public TestSoapHeaderTypeValuePair A {
      get { return _a; }
      set { _a = value; }
    }

  }

  [XmlType(Namespace = "http://www.example.com/namespace")]
  public class TestSoapHeaderTypeValuePair {
    private string _type;
    private string _value;

    [XmlNamespaceDeclarations]
    public XmlSerializerNamespaces xmlsn
    {
      get
      {
        XmlSerializerNamespaces xsn = new XmlSerializerNamespaces();
        xsn.Add("ex", "http://www.example.com/namespace");
        return xsn;
      }
      set { }
    }

    public TestSoapHeaderTypeValuePair(string type, string value) {
      Type = type;
      Value = value;
    }

    public TestSoapHeaderTypeValuePair() {}

    [System.Xml.Serialization.XmlAttributeAttribute("type", Namespace = "http://www.example.com/namespace")]
    public string Type {
      get { return _type; }
      set { _type = value; }
    }

    [System.Xml.Serialization.XmlText()]
    public string Value {
      get { return _value; }
      set { _value = value; }
    }
  }

This is what I get:
 
<ex:test soap:mustUnderstand="1" xmlns:ex="http://www.example.com/namespace">
  <ex:A Type="lorem">ipsum</ex:A>
</ex:test>
 
This is what I want: (Note that the Type-attribute is prefixed with ex.)
 
<ex:test soap:mustUnderstand="1" xmlns:ex="http://www.example.com/namespace">
  <ex:A ex:Type="lorem">ipsum</ex:A>
</ex:test>
 
This is my code:
 
  [XmlType(Namespace = "http://www.example.com/namespace")]
  [XmlRoot("ex", Namespace = "http://www.example.com/namespace")]
  public class TestSoapHeader : SoapHeader {
    private TestSoapHeaderTypeValuePair _a;

    public TestHeader() {
      MustUnderstand = true;
    }

    [XmlNamespaceDeclarations]
    public XmlSerializerNamespaces xmlsn {
      get {
        XmlSerializerNamespaces xsn = new XmlSerializerNamespaces();
        xsn.Add("ex", "http://www.example.com/namespace");
        return xsn;
      }
      set { }
    }

    public TestSoapHeaderTypeValuePair A {
      get { return _a; }
      set { _a = value; }
    }

  }

  [XmlType(Namespace = "http://www.example.com/namespace")]
  public class TestSoapHeaderTypeValuePair {
    private string _type;
    private string _value;

    [XmlNamespaceDeclarations]
    public XmlSerializerNamespaces xmlsn
    {
      get
      {
        XmlSerializerNamespaces xsn = new XmlSerializerNamespaces();
        xsn.Add("ex", "http://www.example.com/namespace");
        return xsn;
      }
      set { }
    }

    public TestSoapHeaderTypeValuePair(string type, string value) {
      Type = type;
      Value = value;
    }

    public TestSoapHeaderTypeValuePair() {}

    [System.Xml.Serialization.XmlAttributeAttribute("type", Namespace = "http://www.example.com/namespace")]
    public string Type {
      get { return _type; }
      set { _type = value; }
    }

    [System.Xml.Serialization.XmlText()]
    public string Value {
      get { return _value; }
      set { _value = value; }
    }
  }