Displaying mobile friendly page without changing the URL in ASP.NET with C# (NO CSS)

Objective

1. Detecting mobile request using a plugin (simple, easy, reliable and free)
2. Sending mobile request to a mobile page developed for mobile screen (internally, without changing the URL)
3. Sending response to the users browser that is purely for mobile with no extra content

Using the code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : ParentPage
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
}

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Web;
using FiftyOne.Foundation.Mobile.Detection;

/// <summary>
/// Summary description for ParentPage
/// </summary>
public class ParentPage : System.Web.UI.Page
{
    public ParentPage()
    {
        string screen = string.Empty;

        bool isMobile = this.Context.Request.Browser["IsMobile"] == "True";

        if (isMobile) // if coming from Mobile device
        {
            screen = "handheld";
            SetScreenSpecificPageSettings(screen);
        }
        else // if user has selected to view mobile version from Desktop
        {
            if (this.Context.Request.Cookies["screen"] != null || !string.IsNullOrWhiteSpace(this.Context.Request.QueryString["screen"]))
            {
                if (!string.IsNullOrWhiteSpace(this.Context.Request.QueryString["screen"]))
                {
                    screen = this.Context.Request.QueryString["screen"];
                    // create the cookies for subsequent request
                    this.Context.Response.Cookies["screen"].Value = this.Context.Request.QueryString["screen"];
                }
                else if (this.Context.Request.Cookies["screen"] != null)
                {
                    screen = this.Context.Request.Cookies["screen"].Value;
                }
                SetScreenSpecificPageSettings(screen);
            }
        }
    }

    private void SetScreenSpecificPageSettings(string screen)
    {
        if (screen.Equals("handheld", StringComparison.CurrentCultureIgnoreCase)) // if coming to Mobile screen, redirect to mobile page
        {
            // frame the mobile page name for this page
            var pathWithFile = string.Empty;
            if (Page.RouteData.RouteHandler == null)
            {
                pathWithFile = this.Context.Request.Url.AbsolutePath;
            }
            else
            {
                pathWithFile = ((System.Web.Routing.PageRouteHandler)Page.RouteData.RouteHandler).VirtualPath;
            }
            var extensionLength = Path.GetExtension(pathWithFile).Length;
            var mobilePage = pathWithFile.Substring(0, (pathWithFile.Length - extensionLength)) + "M" + Path.GetExtension(pathWithFile);

            var physicalFile = Server.MapPath(mobilePage);

            if (File.Exists(physicalFile)) // transfer only when the file exists for the Handheld device
            {
                this.Context.Server.Transfer(mobilePage + this.Context.Request.Url.Query, true);
            }
        }
    }
}

1. System.IO - to get the file extension
2. FiftyOne.Foundation.Mobile.Detection - to detect whether request is coming from mobile device 

1. We can have separate MasterPages for Desktop and Mobile for total control, easy implementation and maintenance.
   
   
2. We can have separate style sheets for Desktop and Mobile to make them lightweight and load only those .css that is required for either Desktop or Mobile.
   
   
3. As Desktop and Mobile pages are two separate physical pages so we have complete control and total freedom to render the data in the way we want and write only code that is applicable for respective version of the page that ultimately makes it easy to load and perform better.
   
   
4. The URL doesn't change, not even querystring is needed to denote that whether to render a page for Desktop or Mobile. The link at the footer of the page is just to given an option to the user in case he/she wants to browser mobile version of the page on Desktop explicitly.

Conclusion