反序列化返回空键和空值（计数正确）

Question

我正在尝试C＃序列化，并且不得不序列化一个Dictionary，因为它不能序列化，所以我使用了XML字符串，然后对它进行了反序列化（示例取自https://blogs.msdn.microsoft.com/adam/2010/09/10/how-to-serialize-a-dictionary-or-hashtable-in-c/）

DictionaryDataItem类：

[Serializable]
public class DictionaryDataItem
{
    public string Key;

    public string Value;

    public DictionaryDataItem(string key, string value)
    {
        Key = key;
        Value = value;

    }

    public DictionaryDataItem()
    {
        Key = "";
        Value = "";
    }
}

序列化代码：

[WebMethod]
public string ListarPaises()
{
    List<DictionaryDataItem> Paises = new List<DictionaryDataItem>();

    XmlSerializer serializer = new XmlSerializer(typeof(List<DictionaryDataItem>));
    StringWriter sw = new StringWriter();
    XmlSerializerNamespaces ns = new XmlSerializerNamespaces();
    ns.Add("", "");
    try
    {
        Dictionary<string, string> diccionario = FabricaLogica.getLogicaGeneral().ListarPaises();

        foreach (string key in diccionario.Keys)
        {
            Paises.Add(new DictionaryDataItem(key, diccionario[key]));
        }

        serializer.Serialize(sw, Paises, ns);
    } catch (Exception ex)
    {
        ThrowSoapException(ex);
    }
    return sw.ToString();
}

序列化有效，它返回以下字符串作为xml：

<string xmlns="http://tempuri.org/">
<?xml version="1.0" encoding="utf-16"?>
<ArrayOfDictionaryDataItem>
    <DictionaryDataItem>
        <Key>ARG</Key>
        <Value>ARGENTINA</Value>
    </DictionaryDataItem>
    <DictionaryDataItem>
        <Key>BRA</Key>
        <Value>BRASIL</Value>
    </DictionaryDataItem>
    <DictionaryDataItem>
        <Key>URU</Key>
        <Value>URUGUAY</Value>
    </DictionaryDataItem>
</ArrayOfDictionaryDataItem>
</string>

然后，我的反序列化代码：

Dictionary<string, string> Paises = new Dictionary<string, string>();

string RawData = new WebService.WebService().ListarPaises();

XmlSerializer xs = new XmlSerializer(typeof(List<DictionaryDataItem>));
StringReader sr = new StringReader(RawData);
List<DictionaryDataItem> templist = (List<DictionaryDataItem>)xs.Deserialize(sr);

foreach (DictionaryDataItem di in templist)
{
    Paises.Add(di.Key, di.Value);
}

return Paises;

我可以看到templist有3个项目，但是所有项目的键和值都为空。

我想念什么吗？