c#序列化xmlwriter stringwriter大对象内存不足帮助

我正在管理一个大型项目，需要序列化和发送xml格式的对象。

(注意:我没有写这个项目，所以在这个方法之外进行编辑，或者彻底改变架构不是一个选择。它通常工作得很好，但当对象这么大时，它会抛出内存异常。我需要用另一种方法来处理大对象

当前代码是:

public static string Serialize(object obj)
{
    string returnValue = null;
    if (null != obj)
    {
        System.Runtime.Serialization.DataContractSerializer formatter = new System.Runtime.Serialization.DataContractSerializer(obj.GetType());
        XDocument document = new XDocument();
        System.IO.StringWriter writer = new System.IO.StringWriter();
        System.Xml.XmlTextWriter xmlWriter = new XmlTextWriter(writer);
        formatter.WriteObject(xmlWriter, obj);
        xmlWriter.Close();
        returnValue = writer.ToString();
    }
    return returnValue;
}

在returnValue = writer.ToString()处抛出内存不足异常。

我重写了它，使用我喜欢的"using"块:

public static string Serialize(object obj)
    {
        string returnValue = null;
        if (null != obj)
        {
            System.Runtime.Serialization.DataContractSerializer formatter = new System.Runtime.Serialization.DataContractSerializer(obj.GetType());
            using (System.IO.StringWriter writer = new System.IO.StringWriter())
            {
                using (System.Xml.XmlTextWriter xmlWriter = new XmlTextWriter(writer))
                {
                    formatter.WriteObject(xmlWriter, obj);
                    returnValue = writer.ToString();
                }
            }
        }
        return returnValue;
    }

研究这一点，似乎StringWriter上的ToString方法实际上使用了两倍的RAM。(我实际上有足够的RAM自由，超过4 gb，所以不确定为什么我得到内存不足的错误)。

public static void Serialize(object obj, FileInfo destination)
{
    if (null != obj)
    {
        using (TextWriter writer = new StreamWriter(destination.FullName, false))
        {
            XmlTextWriter xmlWriter = null;
            try
            {
                xmlWriter = new XmlTextWriter(writer);
                DataContractSerializer formatter = new DataContractSerializer(obj.GetType());
                formatter.WriteObject(xmlWriter, obj);
            }
            finally
            {
                if (xmlWriter != null)
                {
                    xmlWriter.Flush();
                    xmlWriter.Close();
                }
            }
        }
    }
}