最近在公司写API，为了方便调用，接口可以选择返回XML或者JSON二种类型，在使用c#中的XmlSerializer对字典对外象（Hashtable或Dictionary等）进行序列化时，会抛出异常（不支持类型 ***，因为它实现 IDictionary。）.
搜索了一下，原来是IDictionary对象反射时Item属性存在重载（索引器是通过getItem取值的），导致无法正确取值！

　　解决方法很简单，我们只要建新一个类型，派生自原类型并实现IXmlSerializable即可，以下分别以Hashtable与Dictionary<TKey,TValue>为例，演示如何解决访问题！

　　Dictionary:

    public class SerializableDictionary<TKey, TValue> : Dictionary<TKey, TValue>, IXmlSerializable  
    {
        #region IXmlSerializable 成员

        public System.Xml.Schema.XmlSchema GetSchema()
        {
            return null;
        }

        public void ReadXml(System.Xml.XmlReader reader)
        {
            XmlSerializer keySerializer = new XmlSerializer(typeof(TKey));
            XmlSerializer valueSerializer = new XmlSerializer(typeof(TValue));
            bool isEmpty = reader.IsEmptyElement;
            reader.Read();
            if (isEmpty)
                return;
            while (reader.NodeType != System.Xml.XmlNodeType.EndElement)
            {
                reader.ReadStartElement("item");
                reader.ReadStartElement("key");
                TKey key = (TKey)keySerializer.Deserialize(reader);
                reader.ReadEndElement();
                reader.ReadStartElement("value");
                TValue value = (TValue)valueSerializer.Deserialize(reader);
                reader.ReadEndElement();
                this.Add(key, value);
                reader.ReadEndElement();
                reader.MoveToContent();
            }
            reader.ReadEndElement();  

        }

        public void WriteXml(System.Xml.XmlWriter writer)
        {
            XmlSerializer keySerializer = new XmlSerializer(typeof(TKey));
            XmlSerializer valueSerializer = new XmlSerializer(typeof(TValue));
            foreach (TKey key in this.Keys)
            {
                writer.WriteStartElement("item");
                writer.WriteStartElement("key");
                keySerializer.Serialize(writer, key);
                writer.WriteEndElement();
                writer.WriteStartElement("value");
                TValue value = this[key];
                valueSerializer.Serialize(writer, value);
                writer.WriteEndElement();
                writer.WriteEndElement();
            }  

        }

        #endregion
    }

　　Hashtable:

    public class SerializableHashtable : System.Collections.Hashtable, IXmlSerializable
    {
        #region IXmlSerializable 成员

        public System.Xml.Schema.XmlSchema GetSchema()
        {
            return null;
        }


        private XmlSerializer serializer = new XmlSerializer(typeof(object));



        public void ReadXml(System.Xml.XmlReader reader)
        {
            bool isEmpty = reader.IsEmptyElement;
            reader.Read();
            if (isEmpty)
                return;
            while (reader.NodeType != System.Xml.XmlNodeType.EndElement)
            {
                reader.ReadStartElement("item");
                reader.ReadStartElement("key");
                object key = serializer.Deserialize(reader);
                reader.ReadEndElement();
                reader.ReadStartElement("value");
                object value = serializer.Deserialize(reader);
                reader.ReadEndElement();
                this[key]= value;
                reader.ReadEndElement();
                reader.MoveToContent();
            }
            reader.ReadEndElement();

        }

        public void WriteXml(System.Xml.XmlWriter writer)
        {
            foreach (object key in this.Keys)
            {
                writer.WriteStartElement("item");
                writer.WriteStartElement("key");
                serializer.Serialize(writer, key);
                writer.WriteEndElement();
                writer.WriteStartElement("value");
                object value = this[key];
                serializer.Serialize(writer, value);
                writer.WriteEndElement();
                writer.WriteEndElement();
            }

        }

        #endregion
    }

　　使用示例：

                SerializableHashtable sh = new SerializableHashtable();
                sh["ret"] = "0";
                sh["msg"] = "序列化Hashtable测试";

                XmlSerializer sr = new XmlSerializer(sh.GetType());
                sr.Serialize(Response.Output, sh);

　　输出XML：

<?xml version="1.0" encoding="utf-8"?>
<SerializableHashtable>
  <item>
    <key>
      <string>msg</string>
    </key>
    <value>
      <string>序列化Hashtable测试</string>
    </value>
  </item>
  <item>
    <key>
      <string>ret</string>
    </key>
    <value>
      <string>0</string>
    </value>
  </item>
</SerializableHashtable>