使用LINQ to XML时如何检查XML是否包含元素？

Given this structure:

鉴于这种结构：

 <root>
     <user>
           <userName>user1</userName>
           <userImageLocation>/user1.png</userImageLocation>
     </user>
     <user>
           <userName>user2</userName>
     </user>
 </root>

public class User
{
    public string UserName {get; set; }
    public string UserImageLocation {get; set; }
}
 <root>