client|聊天室|刷新|无刷新我们在传统的web程序当中比较头疼的一件事是屏幕的刷新感。虽然有server push的技术，但在IE中较难实现。现在webservice给了我们这样一个机会，大家都知道webservice是基于soap的，而soap是xml的应用，如果你曾经用过ms xml sdk3.0的话就会知道里面有个xmlhttp方法，其实在那时我们就已经可以用xmlhttp的方式替代Form了，也是无刷新的，其实准确地说是局部刷新，下面我们来看一下怎样做，先做一个chat webservice, 首先来分析一下，一个聊天室应具备的两个要素人和消息，这样我们可以建立一个类型（记得我在以前说过类也是类型），它包含这样两个要素。
///ChatMessage.cs
using System;

namespace chat
{
    /// <summary>
    /// ChatMessage类封装了两个string变量:UserLists--用户列表，Messages--要传递的信息
    /// </summary>
    public class ChatMessage
    {
        public string UserList, Messages;
    }
}
第二个我们要建立的是什么呢？一个聊天室应能存储在线成员的名字及访问时间
///Member.cs
using System;

namespace chat
{
    /// <summary>
    /// Member类为每个聊天者封装了Server端的变量
    /// </summary>
    public class Member
    {
        // 存储消息的队列        
public string UserName, MsgQueue;
                // 判断滞留事件以便踢人
        public System.DateTime LastAccessTime;
        // The constructor
        public Member(string NickName)
        {
            this.UserName=NickName;
            this.LastAccessTime=DateTime.Now;
        }
    }
}

接下来我们就应该做这个asmx了
///ChatWebService.asmx
using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
using System.Web;
using System.Web.Services;

namespace chat
{
    /// <summary>
    /// Summary description for ChatWebService.
    /// </summary>
    [WebService (Namespace = "http://localhost/chat/", Description = "This service provides an chat service")]
    public class ChatWebService : System.Web.Services.WebService
    {
        public ChatWebService()
        {
            //CODEGEN: This call is required by the ASP.NET Web Services Designer
            InitializeComponent();
        }

        #region Component Designer generated code
        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
        }
        #endregion

        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        protected override void Dispose( bool disposing )
        {
        }
        
        [WebMethod(Description="接收用户名作为参数存储到Application对象中")]
        public string Login(string username)
        {
            // Ascertain that all the registered chat participants are active
            CheckMembersList();
            // Synchronization Lock
            Application.Lock();
            // Get the collection of keys for the Application Variables
            String[] Members = Application.AllKeys;
            // Are there any registered chat members? & the present request is for a unique nick name?
            if ((Members.Length>0)&&(Array.IndexOf(Members,username)>-1))
            {
                throw new Exception("该用户已存在！");
            }
            // Create a new Member object for this participant
            Member NewMember = new Member(username);
            // Add this new member to the collectionof Application Level Variables
            Application.Add(username, NewMember);
            // Synchronization unlock
            Application.UnLock();
            // Go and get the list of current chat participants and retrun the list
            return GetMembersList();
        }

        [WebMethod(Description="GetMsg方法用用户名和消息为参数返回一个ChatMessage对象，包括要传递的消息和用户列表")]
        public ChatMessage XchangeMsgs(string username, string Msg)
        {
            // Ascertain that all the registered chat participants are active
            CheckMembersList();
            // Synchronization Lock
            Application.Lock();
            // Get the collection of keys for the Application Variables
            String[] Members = Application.AllKeys;
            if ((Members.Length==0)||(Array.IndexOf(Members,username)==-1))
                // Are there any registered chat members? & the present request is for a unique nick name?
            {
                throw new Exception("你当前可能没有登陆或登陆超时，请重新登陆！");
            }
                        ChatMessage RetMsg = new ChatMessage();

            RetMsg.UserList = GetMembersList();
            // Loop through all the Chat Participant's serverside Member Objects and
            // add the message just received in their waiting message queue
            for (int x=0;x<Members.Length;x++)
            {
                                Member temp = (Member)Application[Members[x]];
                                temp.MsgQueue+=("
<Font color = Red>" + username + " 说:
</FONT><Font color = Blue>" + Msg);
                                if (temp.UserName == username)
                {
                    RetMsg.Messages = temp.MsgQueue;
                    temp.MsgQueue="";
                    temp.LastAccessTime=DateTime.Now;
                }
            }
            // Synchronization unlock
            Application.UnLock();
            return RetMsg;
        }
        
        [WebMethod(Description="GetMsg方法用username为参数返回一个ChatMessage对象，包括要传递的消息和用户列表")]
        public ChatMessage GetMsgs(string username)
        {
            Application.Lock();
            CheckMembersList();
            Application.Lock();
            String[] Members = Application.AllKeys;
            if ((Members.Length==0)||(Array.IndexOf(Members,username)==-1))
            {
                throw new Exception("Unknown User. Please Login with a UserName");
            }
            ChatMessage RetMsg = new ChatMessage();
            RetMsg.UserList = GetMembersList();
            Member temp = (Member)Application[username];
            RetMsg.Messages = temp.MsgQueue;
            temp.MsgQueue="";
            temp.LastAccessTime=DateTime.Now;
            Application.UnLock();
            return RetMsg;
        }

        public string GetMembersList()
        {
            Application.Lock();
            String UserList = "";
            String[] Members = Application.AllKeys;
            Application.UnLock();
            for (int x=0;x<Members.Length;x++)
            {
                Member temp = (Member)Application[Members[x]];
                UserList += (temp.UserName+"\n");
            }
            return UserList;
        }

        private void CheckMembersList()
        {
            String[] Members = Application.AllKeys;
            ArrayList RemoveList = new ArrayList();
            for (int x=0;x<Members.Length;x++)            
            {
                Member temp = (Member) Application[Members[x]];
                int test = (DateTime.Now.Subtract(temp.LastAccessTime)).Minutes;
                if (test > 2)
                {
                    RemoveList.Add(Members[x]);                    
                }
            }
            // Users = null;
            for (int count = 0;count<RemoveList.Count;count++)
            {
                Application.Remove((String)RemoveList[count]);
            }
            return;
        }

        
    }
}