protected bool AddPizza()

        {

            //初始化id

            int newId;

            string filePath = HttpContext.Current.Server.MapPath("XMLFile.xml");

            //创建XML文件对象的实例doc

            XmlDocument doc = new XmlDocument();

            //加载XML文件

            doc.Load(filePath);

            //获取结点Pizza下的所有子结点

            XmlNodeList nodeList = doc.SelectSingleNode("Pizza").ChildNodes;

            bool isExist = true;

            foreach (XmlElement xe in nodeList)

            {

                isExist = xe.Attributes["size"].Value == tbPizzaSize.Text;

                if (isExist)

                {

                    xe.SetAttribute("price", tbPizzaPrice.Text);

                    doc.Save(filePath);

                }

            }

            if (!isExist)

            {

                if (nodeList.Count > )

                {

                    //查找最后一个结点的id

                    newId = Convert.ToInt32(doc.DocumentElement.SelectSingleNode("/Pizza/Pizzas[last()]").Attributes["id"].Value) + ;

                    //创建一个新的xml元素

                    XmlElement Pizzas = doc.CreateElement("Pizzas");

                    //创建xml属性

                    XmlAttribute id = doc.CreateAttribute("id");

                    XmlAttribute size = doc.CreateAttribute("size");

                    XmlAttribute price = doc.CreateAttribute("price");

                    //给xml属性赋值

                    id.Value = newId.ToString();

                    size.Value = tbPizzaSize.Text;

                    price.Value = tbPizzaPrice.Text;

                    //给结点赋值

                    Pizzas.InnerText = tbPizzaName.Text;

                    //把属性值添加到元素结点里

                    Pizzas.Attributes.Append(id);

                    Pizzas.Attributes.Append(size);

                    Pizzas.Attributes.Append(price);

                    //把元素结点添加到XMl文件里

                    doc.DocumentElement.AppendChild(Pizzas);

                    //保存XML文件

                    doc.Save(filePath);

                }

                else

                {

                    newId = ;

                }

            }

            return true;

        }