XmlDocument doc = new XmlDocument();
            try
            {
                doc.Load("new.xml");
            }
            catch
            {
                XmlTextWriter xtw = new XmlTextWriter("new.xml", Encoding.UTF8);
                //新建XML文件        
                xtw.WriteStartDocument();
                xtw.WriteStartElement("gnode");
                // gnode根节点                 
                xtw.WriteStartElement("myxm1");
                // gnode根节点下的元素myxmls             
                xtw.WriteEndElement();
                xtw.WriteEndElement();
                xtw.WriteEndDocument();
                xtw.Close();
                doc.Load("new.xml");
            }
            XmlNode xn = doc.DocumentElement;
            //找到根节点     
            XmlElement xe = doc.CreateElement("myxml2");
            //在根节点下创建元素，如果是属性，则用XmlAttribute； 
            xe.InnerText = "hahaha";
            //给子节点写入文本节点（值）     
            xn.AppendChild(xe);
            //根节点将其纳入         
            doc.Save("new2.xml");
            //利用XmlDocument保存文件
        }

   using (SqlConnection con = new SqlConnection("Server=.;DataBase=HGSTUDY;uid=sa;pwd=yao"))
            {
                con.Open();
                SqlCommand command = new SqlCommand("select * from GL_STUDY", con);
                command.CommandType = CommandType.Text;
                DataSet ds = new DataSet("DATASET");
                //DATASET将成为XML文件中的根节点名称，否则系统将其命名为NewDataSet      
                SqlDataAdapter sda = new SqlDataAdapter();
                sda.SelectCommand = command;
                sda.Fill(ds, "DATATABLE");
                //DATATABLE为所生成XML文件中的子节点名称，否则系统将其命名为Table。   
                ds.WriteXml("dbxml.xml");
                // DataSet的方法WriteXml将数据写入到XML文件，就是这么一句话。如果不保存到文件，直接ds.GetXML()      
            }

[XmlRoot("Truck")]
                //----设置作为XML中的根元素名称  
        public Truck()   
        { }             
        [XmlAttribute("id")]
        //--------设置作为xml中的属性    
        public int ID    
            {        
                get{return this._id;} 
                set { this._id = value; }   
            }      
        [XmlElement("chepai")]
        //------设置作为XML中的元素（默认状态）  
        public string cheID   
        {          
            get {
                return this._cheID;
            }        
            set {
                this._cheID = value;
            }       
        }       
        private int _id = 0; 
        private string _cheID = "";  

class XXX {  
               XmlSerializer ser = new XmlSerializer(Type.GetType("forxml.truck"));   
               Truck tr = new Truck();     
               tr.ID = 1;    
               tr.cheID = "赣A T34923";
           }