Adding a ProcessContext to ASP.NET

using System;
using System.Web;
using System.Web.UI;
using System.Collections;

namespace Base4.Web.UI
{
	/// <summary>
	/// This class allows you to move data around (without using a database) between Postbacks and Redirects
	/// that are part of the same process and working with the same data.
	/// </summary>
	public class ProcessContext
	{
		public static ProcessContext Current
		{
			get
			{
				//The overhead of creating a ProcessContext is minimal since it is just a proxy to the real data
				//the reason we cache it in the HttpContext is that if we construct a new ProcessContext on each
				//Call to ProcessContext.Current then we call RegisterHiddenField more than once per request
				//which is dangerous... as we may end up storing our data against the wrong ID!
				ProcessContext current = HttpContext.Current.Items["__PROCESSCONTEXT"] as ProcessContext;
				if (current == null)
				{
					current = new ProcessContext();
					HttpContext.Current.Items["__PROCESSCONTEXT"] = current;
				}
				return current;	
			}
		}
		public static string CurrentProcessID
		{
			get
			{
				return Current.ProcessID;
			}
		}
		protected string _processID = null;
		protected Hashtable _items = null;

		/// <summary>
		/// When the ProcessContext is constructed so postbacks function okay without a QUERYSTRING
		/// redirect this Registers a Hidden Field to store the ProcessID in the form.
		/// </summary>
		protected ProcessContext()
		{
			(HttpContext.Current.Handler as Page).RegisterHiddenField("__PROCESSID",ProcessID);
		}
		/// <summary>
		/// Accesses the Hashtable associated with this ProcessContext.
		/// It creates a new Hashtable if not found. The Hashtable is stored in the users Session
		/// keyed on the ProcessContext.ProcessID
		/// </summary>
		public Hashtable Items
		{
			get
			{
				if (_items == null)
				{
					_items = HttpContext.Current.Session[ProcessID] as Hashtable;
					if (_items == null) 
					{
						_items = new Hashtable();
						HttpContext.Current.Session[ProcessID] = _items;
					}
				}
				return _items;
			}
		}
		/// <summary>
		/// Figures out what the ProcessID of the current ProcessContext is
		/// Checking in order -> QueryString, __PROCESSID field, or creating a new GUID
		/// </summary>
		public string ProcessID
		{
			get
			{
				if (_processID == null)
				{
					_processID = HttpContext.Current.Request.QueryString["ProcessID"] as string;
					if (_processID == null)
					{
						_processID = HttpContext.Current.Request.Form["__PROCESSID"] as string;
						if (_processID == null)
						{
							_processID = Guid.NewGuid().ToString();
						}
					}
				}
				return _processID;
			}
		}
		/// <summary>
		/// Convenience access to this.Items[key] using this[key]
		/// </summary>
		public object this[object key]
		{
			get
			{
				return Items[key];
			}
			set
			{
				Items[key] = value;
			}
		}
		/// <summary>
		/// Used to discard all data associated with this process
		/// </summary>
		public void Discard()
		{
			HttpContext.Current.Session.Remove(ProcessID);
		}
		/// <summary>
		/// Used to empty the hashtable associated with this process
		/// </summary>
		public void Clear()
		{
			Items.Clear();
		}
		/// <summary>
		/// Used to decorate a URL with the ProcessID so the ProcessContext
		/// can be transfered to that URL
		/// </summary>
		/// <param name="url"></param>
		public string AttachProcessToUrl(string url)
		{
			if (url.IndexOf("?") == -1) 
				url = url + "?";
			else
				url = url + "&";
			url += string.Format("ProcessID={0}",ProcessID);
			return url;
		}
		/// <summary>
		/// Used to redirect to the URL provided and transfer the ProcessContext
		/// to that URL too.
		/// </summary>
		/// <param name="url"></param>
		/// <param name="endRequest"></param>
		public void Redirect(string url, bool endRequest)
		{
			AttachProcessToUrl(url);
			HttpContext.Current.Response.Redirect(url,endRequest);
		}
	}
}