Adding a ProcessContext to ASP.NET

using System;
using System.Collections;

namespace Base4.Web.UI
{
	/// <summary>
	/// Summary description for ProcessParticipantPage.
	/// </summary>
	public class ProcessParticipantPage: System.Web.UI.Page, IProcessParticipant
	{
		/// <summary>
		/// If the ProcessID is passed to us via the Querystring... attach to that 
		/// ProcessID
		/// </summary>
		protected override void OnInit(EventArgs e)
		{
			ProcessID = Request.QueryString["ProcessID"];
			base.OnInit (e);
		}
		/// <summary>
		/// Since we store the ProcessID in the Viewstate we need to make sure it is available
		/// </summary>
		public override bool EnableViewState
		{
			get{return true;}set{if (value == false) throw new Exception("You can't participate in a process without ViewState being enabled");}
		}

		#region IProcessParticipant Members
		/// <summary>
		/// We use this method to attach a ProcessID to the querystring of a target URL
		/// </summary>
		/// <param name="url">URL to decorate</param>
		/// <returns>decorated URL</returns>
		public string AttachProcessToUrl(string url)
		{
			if (url.IndexOf("?") == -1) 
				url = url + "?";
			else
				url = url + "&";
			return url + string.Format("ProcessID={0}",ProcessID);
		}
		/// <summary>
		/// For clarity we store the ProcessContext in the ViewState...
		/// It is just a GUID so there is almost no overhead
		/// </summary>
		public string ProcessID
		{
			get
			{
				
				if (this.ViewState["ProcessID"] == null)
					this.ViewState["ProcessID"] = Guid.NewGuid().ToString();
				return this.ViewState["ProcessID"] as string;
			}
			set
			{
				if (value == null) return;
				else this.ViewState["ProcessID"] = value;
			}
		}
		/// <summary>
		/// For simplicity lets store the ProcessContext in the Session
		/// However this could be stored just about anywhere...
		/// 
		/// Also for optimum flexibility the ProcessContext is just a Hashtable
		/// </summary>
		public Hashtable ProcessContext
		{
			get
			{
				Hashtable results = Session[ProcessID] as Hashtable;
				if (results == null)
				{
					results = new Hashtable();
					Session[ProcessID] = results;
				}
				return results;
			}
		}

		#endregion
	}
}