app.config 只会在程序启动的时候加载一次。要动态更新可以这样做:
string appPath = System.IO.Path.GetDirectoryName(Reflection.Assembly.GetExecutingAssembly().Location);
string configFile = System.IO.Path.Combine(appPath, "App.config");
ExeConfigurationFileMap configFileMap = new ExeConfigurationFileMap();
configFileMap.ExeConfigFilename = configFile;
System.Configuration.Configuration config = ConfigurationManager.OpenMappedExeConfiguration(configFileMap, ConfigurationUserLevel.None);
config.AppSettings.Settings["YourThing"].Value = "New Value";
config.Save();