为什么此LINQ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();
        }

The xml config file:

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

Why throws the exception: NullReferenceException was unhandled Object reference not set to an instance of an object.

I'm new to LINQ,plz help.

Answer 1

You are accessing only the emailsetting element, which doesn't have an attribute named server or port .
You need to get the attributes from the smtp child element.

Try this:

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();