class Program

{

    static void Main(string[] args)

    {

        // 使用DOM操作，常用的类：XmlDocument、XmlElement、XmlAttribute和XmlText

        // 1.使用XmlDocument创建文档对象

        XmlDocument xdoc = new XmlDocument();

        // 2.创建文档描述

        XmlDeclaration xdecl = xdoc.CreateXmlDeclaration("1.0", "utf-8", null);

        xdoc.AppendChild(xdecl);    // 使用父节点.AppendChild(子节点)

        // 3.创建根节点

        XmlElement xRoot = xdoc.CreateElement("personCollection");

        xdoc.AppendChild(xRoot);

        // 4.创建person

        XmlElement person = xdoc.CreateElement("person");

        xRoot.AppendChild(person);

        // 5.追加id属性

        //XmlAttribute xid = xdoc.CreateAttribute("id");

        //xid.Value = "001";

        //person.SetAttributeNode(xid);

        person.SetAttribute("id", "");

        // 6.在person下面追加name、age和sex

        XmlElement name = xdoc.CreateElement("name");

        person.AppendChild(name);

        XmlElement age = xdoc.CreateElement("age");

        person.AppendChild(age);

        XmlElement sex = xdoc.CreateElement("sex");

        person.AppendChild(sex);            

        // 7.给name、age和sex等元素追加数据

        XmlText xname = xdoc.CreateTextNode("admin");

        name.AppendChild(xname);

        XmlText xage = xdoc.CreateTextNode("");

        age.AppendChild(xage);

        XmlText xsex = xdoc.CreateTextNode("男");

        sex.AppendChild(xsex);

        // 保存文档

        xdoc.Save("XmlDocumentDemo.xml");

    }

}

<Users>

  <User>admin</User>

  <User>test</User>

  <User>emplorer</User>

</Users>

using System;

using System.Collections.Generic;

using System.IO;

using System.Xml;

namespace ConsoleApplication1

{

    public class UserHelper

    {

        public static string BASEPATH = AppDomain.CurrentDomain.BaseDirectory + @"Users";

        /// <summary>

        /// 所有的登录用户列表添加根节点

        /// </summary>

        public static void InitLoginUsers()

        {

            string userspath = BASEPATH + @"\All Users\Users.xml";

            if (!File.Exists(userspath))

            {

                string allUserFolderPath = BASEPATH + @"\All Users";

                Directory.CreateDirectory(allUserFolderPath);

                FileStream fs = File.Create(userspath);

                fs.Close();

            }

            // 1.使用XmlDocument创建文档对象

            XmlDocument xmlDoc = new XmlDocument();

            // 2.创建文档描述

            //XmlDeclaration xxmlDecl = xmlDoc.CreateXmlDeclaration("1.0", "utf-8", null);

            //xmlDoc.AppendChild(xxmlDecl);    // 使用父节点.AppendChild(子节点)

            XmlElement root = GetElement(xmlDoc, "Users");

            root.InnerText = "";

            xmlDoc.AppendChild(root);

            // 保存文档

            xmlDoc.Save(userspath);

        }

        /// <summary>

        /// 判断节点是否存在(用于Users列表)

        /// 不存在 是就返回创建的一个新节点

        /// 存在   返回相应的节点

        /// </summary>

        /// <param name="xmlDoc"></param>

        /// <param name="node"></param>

        /// <returns></returns>

        private static XmlElement GetElement(XmlDocument xmlDoc, string node)

        {

            XmlElement xmlElement = null;

            if (xmlDoc.SelectSingleNode(node) == null)

            {

                xmlElement = xmlDoc.CreateElement(node);

                xmlElement.InnerText = "";

                xmlDoc.AppendChild(xmlElement);    // 创建根节点

                //xml.DocumentElement.AppendChild(xmlElement);    // 在根节点下添加子节点

            }

            else

            {

                xmlElement = (XmlElement)xmlDoc.SelectSingleNode(node);

            }

            return xmlElement;

        }

        /// <summary>

        /// 用户列表 添加一个新用户

        /// </summary>

        /// <param name="loginName"></param>

        public static void AddNewUser(string loginName)

        {

            string userspath = BASEPATH + @"\All Users\Users.xml";

            XmlDocument xmlDoc = new XmlDocument();                        //建立XmlDomcument对象

            xmlDoc.Load(userspath);

            XmlNode root = GetElement(xmlDoc, "Users");

            // 创建User

            XmlElement user = xmlDoc.CreateElement("User");

            user.InnerText = loginName;

            root.AppendChild(user);

            // 保存文档

            xmlDoc.Save(userspath);

        }

        /// <summary>

        /// 删除一个用户

        /// </summary>

        /// <param name="loginname"></param>

        public static void DeleteUserByName(string loginname)

        {

            string userspath = BASEPATH + @"\All Users\Users.xml";

            XmlDocument xmlDoc = new XmlDocument();                        //建立XmlDomcument对象

            xmlDoc.Load(userspath);

            XmlNode root = GetElement(xmlDoc, "Users");

            XmlNodeList xList = root.SelectNodes("User");

            foreach (XmlNode xNode in xList)

            {

                if (xNode.InnerText.Equals(loginname))

                {

                    xNode.ParentNode.RemoveChild(xNode);

                }

            }

            xmlDoc.Save(userspath);

        }

        /// <summary>

        /// 获取所有的用户信息

        /// </summary>

        /// <returns></returns>

        public static List<string> SelectAllUsers()

        {

            List<string> listUsers = new List<string>();

            string userinfopath = BASEPATH + @"\All Users\Users.xml";

            if (File.Exists(userinfopath))

            {

                XmlDocument xmlDoc = new XmlDocument();

                if (!CheckFile(userinfopath, ))

                    InitLoginUsers();

                xmlDoc.Load(userinfopath);

                XmlNode root = GetElement(xmlDoc, "Users");

                if (root != null)

                {

                    XmlNodeList xList = root.SelectNodes("User");

                    foreach (XmlNode xNode in xList)

                    {

                        listUsers.Add(xNode.ChildNodes.Item().InnerText);

                    }

                }

                xmlDoc.Save(userinfopath);

            }

            return listUsers;

        }

        /// <summary>

        /// 检验文件是否是初始化的

        /// </summary>

        /// <param name="filePath">文件路径</param>

        /// <param name="type">1是个人信息，0是用户列表</param>

        /// <returns>合法是TRUE,非法是FALSE</returns>

        public static bool CheckFile(string filePath, int type)

        {

            using (StreamReader sr = new StreamReader(filePath))

            {

                string str = sr.ReadToEnd().Trim();

                if (type == )

                {

                    if (str.StartsWith("<PersonalConfig>") && str.Length >  && str.EndsWith("</PersonalConfig>"))

                    {

                        return true;

                    }

                }

                else if (type == )

                {

                    if (str.StartsWith("<Users>") && str.Length >  && str.EndsWith("</Users>"))

                    {

                        return true;

                    }

                }

            }

            return false;

        }

    }

}