C#读写操作app.config中的数据

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <connectionStrings>
    <add name="sqlserver" connectionString="Data Source=WT01395sqlexpress;Initial Catalog=mydb;Integrated Security=True"/>
  </connectionStrings>
  <appSettings>
    <add key=""/>
  </appSettings>
</configuration>

引入Configuration的 References库
读取
string conStr = ConfigurationManager.ConnectionStrings["sqlserver"].ToString();

用于保存数据
写入  
Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
            config.AppSettings.Settings.Remove("lastLoginUser");
            config.AppSettings.Settings.Add("lastLoginUser", userName);
            config.Save();
只会把值写入到OesShareUI.exe.Config  不会写在 源文件上