XML 操作(判断用户登录)

    private string usernames = "";
    private string passwords = "";
    private XmlDocument XmlDoc;
    protected void Page_Load(object sender, EventArgs e)
    {
        usernames = Request.QueryString["username"];
        passwords = Request.QueryString["pwd"];
        if (!IsPostBack)
        {
            loadXml();
            XmlNodeList nodeList = XmlDoc.SelectSingleNode("Users").ChildNodes;
            foreach (XmlNode xn in nodeList)
            {
                XmlElement xe = (XmlElement)xn;
                if (xe.HasChildNodes)
                {
                    string username = "";
                    string pwd = "";
                    foreach (XmlNode xx in xe.ChildNodes)
                    {
                        XmlElement ee = (XmlElement)xx;
                        if (ee.Name == "username")
                        {
                            username = ee.InnerText;
                        }
                        if (ee.Name == "password")
                        {
                            pwd = ee.InnerText;
                        }
                    }
                    if (username == usernames)
                    {
                        if (xe.HasAttribute("Count") && xe.GetAttributeNode("Count").Value == "3"
                            && xe.HasAttribute("LoginDate")
                            && DateTime.Parse(xe.GetAttributeNode("LoginDate").Value).AddMinutes(1) >= DateTime.Now)
                        {
                            Response.Write("请一分钟后再尝试登陆");
                        }
                        if (pwd == passwords)
                        {
                            xe.RemoveAttribute("Count");
                            xe.RemoveAttribute("LoginDate");
                            XmlDoc.Save(Server.MapPath("User.xml"));
                            //Response.Redirect("Default2.aspx");
                            Response.Write("登陆成功");
                        }
                        else
                        {
                            if (xe.HasAttribute("Count"))
                            {
                                if (Convert.ToInt32(xe.Attributes["Count"].InnerText) <= 2)
                                    xe.Attributes["Count"].InnerText = (Convert.ToInt32(xe.Attributes["Count"].InnerText) + 1).ToString();
                                else if (Convert.ToInt32(xe.Attributes["Count"].InnerText) > 3)
                                    xe.Attributes["Count"].InnerText = "1";

                            }
                            else
                            {
                                xe.SetAttribute("Count", "1");
                            }
                            if (!xe.HasAttribute("LoginDate"))
                            {
                                xe.SetAttribute("LoginDate", DateTime.Now.ToString());
                            }
                            else if (DateTime.Parse(xe.GetAttributeNode("LoginDate").Value).AddMinutes(1) < DateTime.Now)
                            {
                                xe.RemoveAttribute("Count");
                                xe.RemoveAttribute("LoginDate");
                            }
                            XmlDoc.Save(Server.MapPath("User.xml"));
                        }
                    }
                }
            }
        }
    }

    public void loadXml()
    {
        XmlDoc = new XmlDocument();
        XmlDoc.Load(Server.MapPath("User.xml"));
    }