App.config 读写 保存

            System.Configuration.Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None); //打开config文件

            config.AppSettings.Settings["username"].Value = “username”;         //写入

            config.Save(ConfigurationSaveMode.Modified);                                //保存
            
            string username = config.AppSettings.Settings["username"].Value ;          //读出