AppConfig 写操作

            Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
            config.AppSettings.Settings["code"].Value = DateTime.Now.ToString();
            config.ConnectionStrings.ConnectionStrings["orgcon"].ConnectionString = DateTime.Now.ToString();
            config.Save();
            ConfigurationManager.RefreshSection("appSettings");
            ConfigurationManager.RefreshSection("connectionStrings");