将xml格式的string格式化，方便阅读。

        public XmlDocument GetXmlDocument(string xmlString)
        {
            XmlDocument document = new XmlDocument();
            document.LoadXml(xmlString);
            return document;
        }

        public string ConvertXmlDocumentTostring(XmlDocument xmlDocument)
        {
            MemoryStream memoryStream = new MemoryStream();
            XmlTextWriter writer = new XmlTextWriter(memoryStream, null)
            {
                Formatting = Formatting.Indented//缩进
            };
            xmlDocument.Save(writer);
            StreamReader streamReader = new StreamReader(memoryStream);
            memoryStream.Position = 0;
            string xmlString = streamReader.ReadToEnd();
            streamReader.Close();
            memoryStream.Close();
            return xmlString;
        }

        public string FormatXMLstring(string XMLstring)
        {
            XmlDocument xmlDocument = GetXmlDocument(XMLstring);
            return ConvertXmlDocumentTostring(xmlDocument);
        }