config

https://www.cnblogs.com/dayang12525/p/7866766.html

https://www.cnblogs.com/davytitan/p/4081573.html

https://www.cnblogs.com/tuyile006/archive/2008/06/22/1227667.html

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
  </startup>
  <appSettings>
    <add key="Setting1" value="May 5, 2014"/>
    <add key="Setting2" value="May 6, 2014"/>
  </appSettings>
</configuration>

    class Program
    {
        static void Main(string[] args)
        {
            ReadAllSettings();
            ReadSetting("Setting1");
            ReadSetting("NotValid");
            AddUpdateAppSettings("NewSetting", "May 7, 2014");
            AddUpdateAppSettings("Setting1", "May 8, 2014");
            ReadAllSettings();
            Console.ReadLine();
        }

        static void ReadAllSettings()
        {
            try
            {
                var appSettings = ConfigurationManager.AppSettings;

                if (appSettings.Count == 0)
                {
                    Console.WriteLine("AppSettings is empty.");
                }
                else
                {
                    foreach (var key in appSettings.AllKeys)
                    {
                        Console.WriteLine("Key: {0} Value: {1}", key, appSettings[key]);
                    }
                }
            }
            catch (ConfigurationErrorsException)
            {
                Console.WriteLine("Error reading app settings");
            }
        }

        static void ReadSetting(string key)
        {
            try
            {
                var appSettings = ConfigurationManager.AppSettings;
                string result = appSettings[key] ?? "Not Found";
                Console.WriteLine(result);
            }
            catch (ConfigurationErrorsException)
            {
                Console.WriteLine("Error reading app settings");
            }
        }

        static void AddUpdateAppSettings(string key, string value)
        {
            try
            {
                var configFile = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
                var settings = configFile.AppSettings.Settings;
                if (settings[key] == null)
                {
                    settings.Add(key, value);
                }
                else
                {
                    settings[key].Value = value;
                }
                configFile.Save(ConfigurationSaveMode.Modified);
                ConfigurationManager.RefreshSection(configFile.AppSettings.SectionInformation.Name);
            }
            catch (ConfigurationErrorsException)
            {
                Console.WriteLine("Error writing app settings");
            }
        }
    }

        public static void SetValue(string key, string value)
        {
            System.Xml.XmlDocument xDoc = new System.Xml.XmlDocument();
            xDoc.Load(HttpContext.Current.Server.MapPath("~/Appssa.config"));
            System.Xml.XmlNode xNode;
            System.Xml.XmlElement xElem1;
            System.Xml.XmlElement xElem2;
            xNode = xDoc.SelectSingleNode("//appSettings");

            xElem1 = (System.Xml.XmlElement)xNode.SelectSingleNode("//add[@key='" + key + "']");
            if (xElem1 != null) xElem1.SetAttribute("value", value);
            else
            {
                xElem2 = xDoc.CreateElement("add");
                xElem2.SetAttribute("key", key);
                xElem2.SetAttribute("value", value);
                xNode.AppendChild(xElem2);
            }
            xDoc.Save(HttpContext.Current.Server.MapPath("~/Apps.config"));
        }