Win Form 项目中app.config读取和修改

看到网上的读写app.config的代码，说是写的时候不能直接用System.Configuration.ConfigurationSettings.AppSettings.Set(AppKey, AppValue)，而要把app.config当作XML文件来写。试了下确实如此，那这个Set()方法提供来是干嘛的？源代码的SelectSingleNode()里写的XPath有问题，就随带看了点XPath基础，修改后如下：

        //读 Config
        public static string GetCfgValue(string AppKey)
        {
            try
            {
                return System.Configuration.ConfigurationSettings.AppSettings.Get(AppKey);
            }
            catch (Exception err)
            {
                throw err;
            }
        }

        //写，引入 System.XML
        public static void SetCfgValue(string AppKey, string AppValue)
        {
            System.Xml.XmlDocument xDoc = new XmlDocument();
            xDoc.Load(System.Windows.Forms.Application.ExecutablePath + ".config");

            XmlNode xNode;
            XmlElement xElemKey;
            XmlElement xElemValue;

            xNode = xDoc.SelectSingleNode("//appSettings");

            xElemKey = (XmlElement)xNode.SelectSingleNode("//add[@key=\"" + AppKey + "\"]");
            if (xElemKey != null) xElemKey.SetAttribute("value", AppValue);
            else
            {
                xElemValue = xDoc.CreateElement("add");
                xElemValue.SetAttribute("key", AppKey);
                xElemValue.SetAttribute("value", AppValue);
                xNode.AppendChild(xElemValue);
            }
            xDoc.Save(System.Windows.Forms.Application.ExecutablePath + ".config");
        }

PS：估计app.config是在程序启动时就载入的，修改后的值要重新运行程序后才能读到。