public static void SetValue(string AppKey, string AppValue)
        {
            XmlDocument xDoc = new XmlDocument();
            //获取可执行文件的路径和名称 
            xDoc.Load(System.Windows.Forms.Application.ExecutablePath + ".config");            XmlNode xNode;
            XmlElement xElem1;
            XmlElement xElem2;
            xNode = xDoc.SelectSingleNode("//appSettings");            xElem1 = (XmlElement)xNode.SelectSingleNode("//add[@key='" + AppKey + "']");
            if (xElem1 != null) xElem1.SetAttribute("value", AppValue);
            else
            {
                xElem2 = xDoc.CreateElement("add");
                xElem2.SetAttribute("key", AppKey);
                xElem2.SetAttribute("value", AppValue);
                xNode.AppendChild(xElem2);
            }
            xDoc.Save(System.Windows.Forms.Application.ExecutablePath + ".config");
        }这段代码是对于配置文件的写操作,我要运用这个的话,我应该怎么打SetValue(string AppKey, string AppValue),我打AppKey时一直提示上下文没有该字符串。读操作又是什么样的?