Magic AJAX: Applying AJAX to your existing Web Pages

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using Ajax;

namespace AJAXTest
{
	/// <summary>
	/// Summary description for BubisChat.
	/// </summary>
	public class BubisChat : System.Web.UI.Page
	{
		protected System.Web.UI.WebControls.TextBox txtName;
		protected System.Web.UI.WebControls.TextBox txtInput;
		protected System.Web.UI.WebControls.Button btnSend;
		protected System.Web.UI.WebControls.ListBox lstNames;
		protected System.Web.UI.WebControls.TextBox txtMsg;
		protected System.Web.UI.WebControls.Button btnChangeName;
		protected System.Web.UI.WebControls.Button btnClear;
		protected System.Web.UI.WebControls.LinkButton lnkRefresh;

		private BubisChatData chatData;
		private string currentName
		{
			get { return (string) chatData.names[Session.SessionID]; }
		}
	
		private void Page_Load(object sender, System.EventArgs e)
		{
			chatData = (BubisChatData) Cache["bubis_chat_data"];
			if (chatData == null)
			{
				chatData = new BubisChatData();
				Cache.Add("bubis_chat_data", chatData, null, DateTime.Now.AddDays(1),
					System.Web.Caching.Cache.NoSlidingExpiration, System.Web.Caching.CacheItemPriority.Default, null);
			}

			txtMsg.Text = chatData.msgText.ToString();

			string name = currentName;
			if (name == null)
			{
				name = txtName.Text;
				int i = 1;
				while (!AddName(name + i))
					i++;

				name += i;
				AddName(name);
			}

			if (!IsPostBack)
				txtName.Text = name;

			ShowNames();

			PutSessionIDInCache();
		}

		private void PutSessionIDInCache()
		{
			string key = "bubischat_sessionid_" + Session.SessionID;
			Context.Cache.Add(key, Session.SessionID, null, DateTime.Now.AddMinutes(Context.Session.Timeout),
				System.Web.Caching.Cache.NoSlidingExpiration, System.Web.Caching.CacheItemPriority.Default, new System.Web.Caching.CacheItemRemovedCallback(chatData.RemovedCallback));
		}

		private bool AddName(string name)
		{
			name = name.Trim();
			if (name == "" || chatData.names.ContainsValue(name))
				return false;

			chatData.names.Add (Session.SessionID, name);

			return true;
		}

		private void ChangeName(string newname)
		{
			chatData.names.Remove (Session.SessionID);
			AddName (newname.Trim());
		}

		private void ShowNames()
		{
			lstNames.Items.Clear();
			SortedList list = new SortedList();
			foreach (string name in chatData.names.Values)
				list.Add (name, null);

			foreach (string name in list.Keys)
				lstNames.Items.Add (name);
		}
        
		#region Web Form Designer generated code
		override protected void OnInit(EventArgs e)
		{
			//
			// CODEGEN: This call is required by the ASP.NET Web Form Designer.
			//
			InitializeComponent();
			base.OnInit(e);
		}
		
		/// <summary>
		/// Required method for Designer support - do not modify
		/// the contents of this method with the code editor.
		/// </summary>
		private void InitializeComponent()
		{    
			this.btnClear.Click += new System.EventHandler(this.btnClear_Click);
			this.btnChangeName.Click += new System.EventHandler(this.btnChangeName_Click);
			this.btnSend.Click += new System.EventHandler(this.btnSend_Click);
			this.Load += new System.EventHandler(this.Page_Load);

		}
		#endregion

		private void btnSend_Click(object sender, System.EventArgs e)
		{
			if (txtInput.Text.Trim() != "")
			{
				if (chatData.msgText.Length > 10000)
					chatData.msgText.Remove (0, 3000);

				chatData.msgText.Append (currentName + ": " + txtInput.Text + "\r\n\r\n");
				txtMsg.Text = chatData.msgText.ToString();

				txtInput.Text = "";
			}
		}

		private void btnChangeName_Click(object sender, System.EventArgs e)
		{
            string name = txtName.Text.Trim();
			if (name == "")
			{
				Response.Write ("Type a name in the box.");
				return;
			}

			if (chatData.names.ContainsValue(name))
			{
				Response.Write ("This name already exists in the list.");
				return;
			}

			chatData.msgText.Append (String.Format("------ {0} changed his name to '{1}' -------\r\n\r\n", currentName, name));
			txtMsg.Text = chatData.msgText.ToString();

			ChangeName(name);
			ShowNames();
		}

		private void btnClear_Click(object sender, System.EventArgs e)
		{
			chatData.msgText.Length = 0;
			txtMsg.Text = "";
		}

		public class BubisChatData
		{
			public System.Text.StringBuilder msgText = new System.Text.StringBuilder();
			public Hashtable names = new Hashtable();

			public void RemovedCallback(String k, Object sessionID, System.Web.Caching.CacheItemRemovedReason r)
			{
				names.Remove (sessionID);
			}
		}
	}
}