A Walkthrough to ASP.NET 4.0 URL Routing

So What is URL Routing:

We access our web application using some URL that is normally the physical path of the of pages.So URL Routing is a way to provide our own URL in lieu of the physical path of the page. One other way, Routing allows us a way to configure our application to accept a requested URL which actually doesn't map to physical files. In terms of security perspective of the application, its important because one can easily know the solution structure of the application.

Why URL Routing: 

In 1999, an usability Jakob Nielson, writeen in his blog "URL as UI" 6 essaential points about url.These are

• A domain name that is easy to remember and easy to spell
• short urls
• easy to type urls
• URLs that visualize site structure
• URLs that are "hackable" to allow users to move to higher levels of the information architecture by hacking off the end of the URL.
• persistent urls that doesn't change

As from all these points, we can see the url is a part of user interface and it should be simple and easy.Urls  also made us visualize the structure of our application which might be security concern for us etc..

ASP.NET 4.0 provides us the feature, taken care all the point mentioned above.

Also these urls helps in SEO(Search engine optimastion) and improve the page hits but putting the appropriate keywords.

URL Routing Earlier: 

Earlier URL routing was not so easy.For that we require to have our own custom handler in a way that whenever a url is requested our custom route handler class should be invoked, and forword the request to appropriate requested page or we could have some third party solution. So lets say if we are going to develop our own custom handler then what we require to do

1. We define the mapping in Global.asax, which maps a route pattern to route handler class.
2. We require to develop a Route handler class which actually receives the URL, parse it,store any route parameters into some location that should be accessible to the requested page and return the instance of requested page or forward the request to the HTTPhandler that handles the requested route.
3. Writing code in the target page in the way so that it can fetch the route parametrs and render the page accordingly.

So you can imagine that it was not a straight forward task.And also require some considerable amount of effort to develop it.

URL Rouing with ASP.NET 4.0: 

As a I already discussed in my introduction section, that ASP.NET 4.0 is provide us a simplified and robust way to handle ht entire URL routing mechanism.To provide URL routing, ASP.NET is now equipped with myriad classes and number of methods to provide this feature, which allows to easliy decouple the url with physical files. We just need to use them.

ASP.NET 4.0 router enables to define any kind of custom routes and we can easliy map to it to our webform page.

ASP.NET 4.0 also made our life simpler by providing us the feature "Bi- Directional routing" with the help of several componants like Route Table, Page Routehandler and ExpressionBuilders.

What is Bi-directional Routing: 

With the help of the Route table we cannot only decode the Routed URL with the help of Route table and with the help of other methods provided by the ASP.NET 4.0, we can also generate the URL with the ASP.NET routing mechanism, which gives us the opportunity, not to hard code the URL at several places, it will be dynamically generated with the help Routing Definition.

So we just require to change the Rout Table on any changes in the URL, and dont need to change it several other places throughout the solution.

Componeants of ASP.NET 4.0 URL Routing: 

There are two main componants of ASP.NET URL Routing.

RoutingHandler: 

Routing is basically a normal HTTPHandler, which is resposible for looking into all the incoming URL request, and look for any Routing definition is available for the URL, if yes then pass the request and data to corresponding resource.

Expression Builders: 

Expressions are provided with ASP.NET 4.0 to facilitate "Bi-Directional Routing" and more. Basically there are two types of ExpressionBuilders.

RoutURLExpressionBuilder:It is as name suggest provides the syntax which results in the value ie URL based on RouteName and Parameter according to the Rout Definitions we have.

RoutValueExpressionBuilder: As above generates the URL,RoutValueExpressionBuilder provided a syntax which recieves the value from the RouteName and Parameter from RoutedURL.

There are also few new properties like HttpRequest.RequestContext and Page.RouteData these provide facilitate to the availability of the parameters to all resorrces.

An example:

First: In this I will be displaying the image and name of the book on  my web page.

Here , I will be going to an asp.net application and will take you a step by step to create the application.

Note:

• I have used VS2010 Beta2 version for this sample.
• we have to use the nameswe have to use the namespace System.Web.Routing in our application to access Routing specific classes and methods.

Step 1: Define the Route in Application_Start of Global.asax. Also include namespace System.Web.Routing.

        void Application_Start(object sender, EventArgs e)
        {
            // Code that runs on application startup
            RouteTable.Routes.MapPageRoute("StoreRoute",
            "BookStore/{Name}",
            "~/Webpages/BookStore/ViewBookDemo.aspx");

        }
        
        

Step 2:  (a) Now in ViewBookDemo.aspx I have four links.In First two, I have hardcoded the URL and In last I used RoutURLExpressionBuilder to generate the URL dynamically. That is known as Bi- Dirctional routing.This is the one I also liked the most, in several case we have had links in our pages those were generally hard coded.

(b) Also, I have a Label in the page and I set the the Text property dynamically with the help of Routing inforamtion as above.

Step 3: In ViewBookDemo.aspx .cs page, I have fetch the parameter from the Routing Table and set the Image1 URL dynamically in the Page_Load as below.(Include namespace System.Web.Routing)

       //fetching the parameter that is Route table
            string name = Page.RouteData.Values["Name"] as string;
            if (name != null)
            {
                if (name == "CSS")
                {
                    Image1.ImageUrl = "~/images/css.jpg";
                }
                else if (name == "Django")
                {
                    Image1.ImageUrl = "~/images/django.jpg";
                }
                else if (name == "IPhone")
                {
                    Image1.ImageUrl = "~/images/iphone.jpg";
                }
                else if (name == "Linq")
                {
                    Image1.ImageUrl = "~/images/Linq.jpg";
                }
            }     
        

To view entire code, please download the attachment.

Now my solution hierarchy is:

And according to it my URL should be "http://localhost:2039/Webpages/BookStore/ViewBome.aspx?Name=CSS"

So here, you can see, Earlier I had use the url "http://localhost:2039/Webpages/BookStore/ViewBome.aspx?Name=CSS" but now with the help of URL Routing my URL is changed to "http://localhost:2039/Bookstore/CSS", which is the main beauty of the URL Routing.

References:
http://haacked.com/archive/2008/03/11/using-routing-with-webforms.aspx

http://haacked.com/archive/2006/11/29/Express_Yourself_With_Custom_Expression_Builders.aspx

http://sankarsan.wordpress.com/2009/08/09/asp-net-4-0-webforms-routing-part-i/

http://weblogs.asp.net/scottgu/archive/2009/10/13/url-routing-with-asp-net-4-web-forms-vs-2010-and-net-4-0-series.aspx