原文地址:https://www.cnblogs.com/Shadow3627/archive/2013/03/26/2983484.html
使用VS 2005以上的版本时，习惯性的使用ConfigurationSettings类来读取应用程序配置文件的信息时，却被编译器提示说
警告“System.Configuration.ConfigurationSettings.GetConfig(string)”已过时:“This method is obsolete, it has been replaced by System.Configuration!System.Configuration.ConfigurationManager.GetSection”
警告 1 “System.Configuration.ConfigurationSettings.AppSettings”已过时:“This method is obsolete, it has been replaced by System.Configuration!System.Configuration.ConfigurationManager.AppSettings”
注意:默认没有引用ConfigurationManager类，所以找不到System.Configuration命名空间的 ConfigurationManager类.
解决:首先添加对System.Configuration.dll 文件的引用:在将"System.Configuration.ConfigurationSettings.GetConfig替换为System.Configuration.ConfigurationManager.GetSection
将“System.Configuration.ConfigurationSettings.AppSettings”替换为System.Configuration.ConfigurationManager.AppSettings”