appsetting詳解

1             // Get the application configuration file.
 2             System.Configuration.Configuration config =
 3               ConfigurationManager.OpenExeConfiguration(
 4                     ConfigurationUserLevel.None);
 5             string sectionName = "appSettings";
 6
 7             NameValueCollection appSettings =
 8                 ConfigurationManager.AppSettings;
 9             List<string> allDatFilesNames;
10
11             allDatFilesNames = GetAllDataFileName();
12             if (allDatFilesNames == null)
13             {
14                 Environment.Exit(0);
15             }
16
17             //先清空之前的數據文件記錄
18             config.AppSettings.Settings.Clear();
19             // Save the configuration file.
20             config.Save(ConfigurationSaveMode.Modified);
21
22             // Force a reload of the changed section. This
23             // makes the new values available for reading.
24             ConfigurationManager.RefreshSection(sectionName);
25             appSettings =
26                 ConfigurationManager.AppSettings;
27
28             foreach (string fullName in allDatFilesNames)
29             {
30                 string fileName = Path.GetFileName(fullName);
31                 if (appSettings[fileName] == null)
32                 {
33                     // 鍵值僅保存文件名 www.2cto.com
34                     config.AppSettings.Settings.Add(fileName, GetFileItemNum(fullName).ToString());
35                 }
36                 else
37                 {
38                     // 已存在此鍵值，則僅刷新
39                     config.AppSettings.Settings[fileName].Value = GetFileItemNum(fullName).ToString();
40                 }
41
42
43             }
44
45             // Save the configuration file.
46             config.Save(ConfigurationSaveMode.Modified);
47
48             // Force a reload of the changed section. This
49             // makes the new values available for reading.
50             ConfigurationManager.RefreshSection(sectionName);

使用appSettings要特別注意，上面代碼中config.AppSettings.Settings和appSettings都能夠索引到鍵值，正常讀取配置文件之後，兩者是一樣的，但是，當執行了上面的config.AppSettings.Settings.Clear();之後，兩者就不同步了，config.AppSettings.Settings（配置文件裡）清空了，但是appSettings（內存裡）還有之前的記錄，(appSettings[fileName] == null)就不一定為true了，這樣直接用config.AppSettings.Settings[fileName].Value添加值，會報null異常。
 
所以還加了上面19~26行部分代碼，而且
appSettings =
                ConfigurationManager.AppSettings;
這個給appSettings重新賦值也是必須的。