public static string Config(string key)         {             ExeConfigurationFileMap file = new ExeConfigurationFileMap();             file.ExeConfigFilename = @"Providers\\Provider.config";             Configuration config = ConfigurationManager.OpenMappedExeConfiguration(file, ConfigurationUserLevel.None);             AppSettingsSection appsection = (AppSettingsSection)config.GetSection("appSettings");             return appsection.Settings[key].Value;         } 

<?xml version="1.0" encoding="utf-8" ?>  <configuration>      <appSettings>          <add key="ConnectionString" value="Server=(local);Database=DB;User Id=sa;Password=123" />      </appSettings>  </configuration> 

//里面的参数为配置文件的key   string strConn=Config("ConnectionString");