为什么这个LINQ会抛出NullReferenceException？

Question

private SmtpClient getServer()
        {
            return (from e in doc.Elements("emailsetting")
                    select new SmtpClient()
                    {
                        Host = e.Attribute("server").Value,
                        Port = Convert.ToInt32(e.Attribute("port").Value)
                    }).FirstOrDefault();
        }

xml配置文件:

  <emailsetting>
    <stmp server="10.182.182.182" port="25" />
    <from address="ithelpdest@citics.com.hk"/>
    <to address=""/>
    <cc address=""/>
  </emailsetting>

为什么抛出异常:NullReferenceException未处理对象引用未设置为对象的实例.

我是LINQ的新手,请帮忙.

Answer 1

您只访问emailsetting没有名为server或的属性的元素port.
您需要从smtp子元素中获取属性.

试试这个:

return (from e in doc.Elements("emailsetting")
        let smtp = e.Element("smtp")
        select new SmtpClient()
        {
            Host = smtp.Attribute("server").Value,
            Port = Convert.ToInt32(smtp.Attribute("port").Value)
        }).FirstOrDefault();