进入.属性[属性名称].ToString() == “mobile” 没有评估为真

namespace SignatureCreator
{
    class Program
    {

        static void Main(string[] args)
        {
            string delimiter = ",";
            // set up domain context
            PrincipalContext ctx = new PrincipalContext(ContextType.Domain);

            // find currently logged in user
            UserPrincipal up = UserPrincipal.Current;
            string displayName = up.DisplayName;
            string title = up.Description;
            string phoneNumber = up.VoiceTelephoneNumber;
            string[] userName = displayName.Split(new string[] { delimiter }, StringSplitOptions.None);
            string firstName = userName[1];
            string lastName = userName[0];
            firstName = firstName.Substring(1);
            firstName = firstName.ToUpper();
            lastName = lastName.ToUpper();
            Console.WriteLine(firstName +" "+ lastName);
            Console.WriteLine(title);
            Console.WriteLine(phoneNumber);
            DirectoryEntry entry = up.GetUnderlyingObject() as DirectoryEntry;
            System.DirectoryServices.PropertyCollection props = entry.Properties;
            /*
             * 
             */
            foreach (string propName in props.PropertyNames)
            {
                if (entry.Properties[propName].ToString() == "mobile")
                {
                    Console.WriteLine(propName + " = " + entry.Properties[propName].Value);
                }
                else
                {
                    Console.WriteLine(propName + " = NULL");
                }
            }

            Console.ReadKey();
            StringBuilder sb = new StringBuilder();
        }
    }
}

我正在尝试循环浏览活动目录信息以查找用户的手机号码。但是我不知道如何循环并返回它。即使我只是评估 propname == 手机，它也不会返回 true。我做错了什么？