关于appsetting

            // Get the application configuration file.
            System.Configuration.Configuration config =
              ConfigurationManager.OpenExeConfiguration(
                    ConfigurationUserLevel.None);
            string sectionName = "appSettings";

            NameValueCollection appSettings =
                ConfigurationManager.AppSettings;
            List<string> allDatFilesNames;

            allDatFilesNames = GetAllDataFileName();
            if (allDatFilesNames == null)
            {
                Environment.Exit(0);
            }

            //先清空之前的数据文件记录
            config.AppSettings.Settings.Clear();
            // Save the configuration file.
            config.Save(ConfigurationSaveMode.Modified);

            // Force a reload of the changed section. This 
            // makes the new values available for reading.
            ConfigurationManager.RefreshSection(sectionName);
            appSettings =
                ConfigurationManager.AppSettings;

            foreach (string fullName in allDatFilesNames)
            {
                string fileName = Path.GetFileName(fullName);
                if (appSettings[fileName] == null)
                {
                    // 键值仅保存文件名
                    config.AppSettings.Settings.Add(fileName, GetFileItemNum(fullName).ToString());
                }
                else
                {
                    // 已存在此键值，则仅刷新
                    config.AppSettings.Settings[fileName].Value = GetFileItemNum(fullName).ToString();
                }


            }

            // Save the configuration file.
            config.Save(ConfigurationSaveMode.Modified);

            // Force a reload of the changed section. This 
            // makes the new values available for reading.
            ConfigurationManager.RefreshSection(sectionName);

使用appSettings要特别注意，上面代码中config.AppSettings.Settings和appSettings都能够索引到键值，正常读取配置文件之后，两者是一样的，但是，当执行了上面的config.AppSettings.Settings.Clear();之后，两者就不同步了，config.AppSettings.Settings（配置文件里）清空了，但是appSettings（内存里）还有之前的记录，(appSettings[fileName] == null)就不一定为true了，这样直接用config.AppSettings.Settings[fileName].Value添加值，会报null异常。

 

所以还加了上面19~26行部分代码，而且

appSettings =

                ConfigurationManager.AppSettings;

这个给appSettings重新赋值也是必须的。