public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        XmlDocument document = new XmlDocument();
        AddElement(document);
        InsertElement(document);
        RepalceElement(document);
    }

    private void AddElement(XmlDocument document)
    {
        XmlElement bookselement = document.CreateElement("books");

        XmlElement bkelement = document.CreateElement("book");
        XmlElement nameelement = document.CreateElement("name");
        nameelement.SetAttribute("id", "1");
        nameelement.InnerText = "C#";
        bkelement.AppendChild(nameelement);

        XmlElement authorelement = document.CreateElement("author");
        authorelement.InnerText = "Microsoft";
        bkelement.AppendChild(authorelement);

        XmlElement priceelement = document.CreateElement("price");
        priceelement.InnerText = "100";
        bkelement.AppendChild(priceelement);

        bookselement.AppendChild(bkelement);
        document.AppendChild(bookselement);

        document.Save(Server.MapPath("books.xml"));
    }

    private void InsertElement(XmlDocument document)
    {
        document.Load(Server.MapPath("books.xml"));
        XmlNode node = document.SelectSingleNode("books");

        XmlElement bkelement = document.CreateElement("book");
        XmlElement nameelement = document.CreateElement("name");

        nameelement.SetAttribute("id", "2");
        nameelement.InnerText = "Java";
        bkelement.AppendChild(nameelement);

        XmlElement authorelement = document.CreateElement("author");
        authorelement.InnerText = "SUN";
        bkelement.AppendChild(authorelement);

        XmlElement priceelement = document.CreateElement("price");
        priceelement.InnerText = "130";
        bkelement.AppendChild(priceelement);

        node.AppendChild(bkelement);

        //Response.Write("node 的 name= " + node.Name);
        //Response.Write("<br>");
        //Response.Write("priceelement 的 name= " + priceelement.Name);
       
        document.Save(Server.MapPath("books.xml"));

    }

    private void RepalceElement(XmlDocument document)
    {
        document.Load(Server.MapPath("books.xml"));

        XmlNodeList nodelist = document.SelectSingleNode("books").ChildNodes;
        XmlElement element;

        foreach (XmlNode node in nodelist)
        {
            element = (XmlElement)node;
            if (element.Name == "author")
            {
                element.InnerText = "波兰";            //这里就没有替换成功。
                break;
            }
            break;
        }

        document.Save(Server.MapPath("books.xml"));
    }
}