C# 读写app.config(xml)

1.读/写connectionStrings/appSettings

 connectionName)
        {
            try
            {
                string connectionString =
                        ConfigurationManager.ConnectionStrings[connectionName].ConnectionString.ToString();
                Console.WriteLine(connectionString);
                return connectionString;
            }
            catch
            {
                return "";
            }
        }

        public static void UpdateConnectionStringsConfig(string newName, string newConString, string newProviderName)
        {
            bool isModified = false;   
            if (ConfigurationManager.ConnectionStrings[newName] != null) 
            {
                isModified = true;
            }
            ConnectionStringSettings mySettings =
                new ConnectionStringSettings(newName, newConString, newProviderName);
            Configuration config =
                ConfigurationManager.OpenExeConfiguration(Application.ExecutablePath);//ConfigurationUserLevel.None
            if (isModified)  
            {
                config.ConnectionStrings.ConnectionStrings.Remove(newName);
            }
            config.ConnectionStrings.ConnectionStrings.Add(mySettings);      
            config.Save(ConfigurationSaveMode.Modified);      
            ConfigurationManager.RefreshSection("ConnectionStrings");
        }

        public static string GetAppSettings(string SettingName)
        {
            return ConfigurationManager.AppSettings[SettingName].ToString();            
        }

        public static void SetAppSettings(string AppKey, string AppValue)
        {
            //System.Configuration.ConfigurationSettings.AppSettings.Set(AppKey,AppValue);
            XmlDocument doc = new XmlDocument();
            doc.Load(Application.ExecutablePath + ".config");
            XmlNode node = doc.SelectSingleNode(@"//add[@key='" + AppKey + "']");
            XmlElement ele = (XmlElement)node;
            if (node != null)
                ele.SetAttribute("value", AppValue);
            else
            {
                XmlElement xElem2;
                xElem2 = doc.CreateElement("add");
                xElem2.SetAttribute("key", AppKey);
                xElem2.SetAttribute("value", AppValue);
                node.AppendChild(xElem2);
            }
            doc.Save(Application.ExecutablePath + ".config");     
        }