XmlSerializer(Type type, Type[] extraTypes) 内存泄漏

在使用XmlSerializer进行序列化或者反序列的时候，对于下面的两个构造方法

XmlSerializer(Type)
XmlSerializer.XmlSerializer(Type, String)

为了提高性能，XML 序列化基础结构将动态生成程序集，以序列化和反序列化指定类型。此基础结构将查找并重复使用这些程序集。

但是对于XmlSerializer(Type type, Type[] extraTypes) 等其他的构造函数，则会生成同一程序集的多个版本，且绝不会被卸载，这将导致内存泄漏和性能降低。

为了解决这个问题代码如下，仅供参考：

static Hashtable ht = new Hashtable();

        /// <summary>
        /// 将指定的对象序列化为XML格式的字符串并返回。
        /// </summary>
        /// <param name="o">待序列化的对象</param>
        /// <returns>返回序列化后的字符串</returns>
        public static string Serialize(Object o, Type[] types = null)
        {
            if (o != null)
            {

                string xml = "";
                XmlSerializer serializer = null;
                try
                {

                    if (types != null)
                    {
                        string names = "";
                        for (int i = 0; i < types.Length; i++)
                        {
                            names = names + types[i].FullName;
                        }
                        XmlSerializerFactory factory = new XmlSerializerFactory();
                        if (ht.ContainsKey(names))
                        {
                            serializer = (XmlSerializer)ht[names];
                        }
                        else
                        {
                            serializer = factory.CreateSerializer(o.GetType(), types);
                            ht.Add(names, serializer);
                        }

                        //  serializer = new XmlSerializer(o.GetType(), types);
                    }
                    else
                    {
                        serializer = new XmlSerializer(o.GetType());
                    }

                    using (MemoryStream mem = new MemoryStream())
                    {
                        using (XmlTextWriter writer = new XmlTextWriter(mem, Encoding.UTF8))
                        {
                            writer.Formatting = Formatting.Indented;
                            XmlSerializerNamespaces n = new XmlSerializerNamespaces();
                            n.Add("", "");
                            serializer.Serialize(writer, o, n);

                            mem.Seek(0, SeekOrigin.Begin);
                            using (StreamReader reader = new StreamReader(mem))
                            {
                                xml = reader.ReadToEnd();
                            }
                        }
                    }
                    types = null;
                    serializer = null;
                }
                catch { xml = ""; serializer = null; }
                return xml;
            }
            else
            {
                return "";
            }
        }