XML檔案如下：

<?xml version="1.0" encoding="utf-8"?>
<root>
 
  <transDate>2014-12-18</transDate>
</root>

 string xmlpath = System.AppDomain.CurrentDomain.BaseDirectory + "config.xml";
            XmlDocument doc = new XmlDocument();
            doc.Load(xmlpath);
            XmlNode xn = doc.SelectSingleNode("//transDate");
            string transDate = xn.InnerText;
 

xn.InnerText = value;
doc.Save(xmlpath);