ASP.NET Optimistic Concurrency Control

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;

namespace Concurrency
{
	/// <summary>
	/// Summary description for BasePage.
	/// </summary>
	public class BasePage : System.Web.UI.Page
	{
		private const string CONCURRENCY_STAMP = "ConcurrencyStamp";		// Keeps the Date time for the lastest object
		private const string CONCURRENCY_OBJECT = "ConcurrencyObject";		// Keeps a reference to the first object read

		private void Page_Load(object sender, System.EventArgs e)
		{
			
		}

		#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.Load += new System.EventHandler(this.Page_Load);

		}
		#endregion

		/// <summary>
		/// Sets the original object
		/// </summary>
		/// <param name="obj">Object to store</param>
		protected void SetConcurrencyObject(BLL.CRUD obj)
		{
			ViewState[CONCURRENCY_OBJECT] = obj;
		}

		/// <summary>
		/// Gets the original object
		/// </summary>
		/// <returns>Object to retrieve</returns>
		protected BLL.CRUD GetConcurrencyObject()
		{
			return ((BLL.CRUD) ViewState[CONCURRENCY_OBJECT]);
		}

		/// <summary>
		/// Shows the fields that have concurrency conflicts
		/// </summary>
		/// <param name="controls">Mapped objects</param>
		protected void ShowConcurrencyFields(Hashtable controls)
		{
			// Retrieve the original object from the view state
			BLL.CRUD userObject = (BLL.CRUD) ViewState[CONCURRENCY_OBJECT];

			// Instantiate an object of the same type and read its properties
			Type type = userObject.GetType();
			BLL.CRUD dbObject = (BLL.CRUD) type.Assembly.CreateInstance(type.FullName);
			dbObject.ID = userObject.ID;
			if (!dbObject.Read())
				Response.Redirect("Error.aspx?msg=" + System.Web.HttpUtility.UrlEncode("The record has been deleted by another user."));

			// Get the product differences
			IList differences = BLL.ObjectDifference.GetDifferences(dbObject, userObject);

			// Reset any previous concurrency style from the page
			ClearPageConcurrency(controls);
			
			foreach (BLL.ObjectDifference diff in differences)
			{
				// Get the control
				WebControl ctrl = controls[diff.PropertyName] as WebControl;
				if (ctrl != null)
				{
					// Change the back color
					ctrl.BackColor = Color.LightGray;
					
					// Check for text boxes
					System.Web.UI.WebControls.TextBox txtBox = ctrl as System.Web.UI.WebControls.TextBox;
					if (txtBox != null)
					{
						txtBox.Text = diff.FirstValue.ToString();
						continue;
					}

					// Check for dropdown lists
					System.Web.UI.WebControls.DropDownList cmbBox = ctrl as System.Web.UI.WebControls.DropDownList;
					if (cmbBox != null)
					{
						cmbBox.Items.FindByText(diff.FirstValue.ToString());
						continue;
					}

					// Check for check boxes
					System.Web.UI.WebControls.CheckBox chkBox = ctrl as System.Web.UI.WebControls.CheckBox;
					if (chkBox != null)
					{
						chkBox.Checked = bool.Parse(diff.FirstValue.ToString());
						continue;
					}

					// ...... Extend to handle other controls .......
				}
			}

			// ViewState[CONCURRENCY_STAMP] = dbObject.Concurrency.ToOADate().ToString();
			ViewState[CONCURRENCY_OBJECT] = dbObject;
		}

		/// <summary>
		/// Resets the page's controls to normal state
		/// </summary>
		/// <param name="controls">Controls on the form</param>
		private void ClearPageConcurrency(Hashtable controls)
		{
			foreach (object obj in controls.Values)
			{
				// Get the control
				WebControl ctrl = obj as WebControl;
				if (ctrl != null)
					ctrl.BackColor = Color.White;
			}
		}
		
	}
}