What is Routing?

Routing is a technique which enables us to use a descriptive,search engine and human friendly URL’s for ASP.Net application to access a resource.In this technique,the URL will not map to a resource physically.

To understand the routing in ASP.Net, we will build a very simple asp.net application that displays list of employees in different departments.

Steps

1. Open Visual Studio 2008.
2. Click New> Website and Select "ASP.Net Web Site".You can select the language of your choice. Rename the website name as per your need.
3. Include a new SQL express database inside App_Data folder and create a table called Employees and Department.

In this example,we will create a simple route that has the department id of the employees in the URL instead of passing it as query string.Refer below pattern,

The valid URL’s for the above routes may be,

Employees/Sales/list.aspx
Employees/HR/list.aspx
Employees/IT/edit.aspx

As we said earlier,we need to first create and register route to a route handler in Global.asax file.In order to register RouteHandler,we need to create the route handler to handle the request that has the url in the following route pattern

"Employees/{Dept}/{action}.aspx"

To do this,right click your solution in solution explorer and include a class file.We have named it as EmployeeRouteHandler.Import the routing namespace System.Web.Routing.Now,inherit the class from IRouteHandler interface and implement GetHttpHanlder() method, which should return the actual page or a handler to handle the request.Refer the code below,

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.Routing;
/// <summary>
/// Summary description for EmployeeRouteHandler
/// </summary>
public class EmployeeRouteHandler: IRouteHandler
{    
  public EmployeeRouteHandler()
   {
      //
      // TODO: Add constructor logic here
      // public class ProductInfoService : System.Web.Services.WebService
   }
   public IHttpHandler GetHttpHandler(RequestContext requestContext)
   {
      string DeptName = requestContext.RouteData.Values["Dept"] as string;
      HttpContext context = HttpContext.Current;
      context.Items.Add("Dept", DeptName);
      string action = requestContext.RouteData.Values["action"] as string;
      if(action.ToLower() == "list")
          return BuildManager.CreateInstanceFromVirtualPath("~/Default.aspx",
          typeof(Page)) as Page;
      else
          return BuildManager.CreateInstanceFromVirtualPath("~/Default.aspx",
          typeof(Page)) as Page;
    }
}

In the above code,we have extracted the place holder value(Department id and action in our case) from the RouteData object.Refer the below line,

string DeptName = requestContext.RouteData.Values["Dept"] as string;
string action = requestContext.RouteData.Values["action"] as string;

The Routing engine will process the incoming URL and will populate the values that are matching the placeholders and will make it available throughout the request.The actual Page object or the target page can be got by calling the CreateInstanceFromVirtualPath() method in BuildManager object.Next,we need to populate the RouteTable with all the possible Routes and RouteHandler object to process the incoming request to the application. To do this,we need to first add a Global.asax file into our solution. Right click the solution, and select “Add New Item”.In the dialog,select “Global Application Class” and click OK.Now,register all the Routes with their corresponding RouteHandler and populate it into the RouteTable object in Application_Start event.It is only "Employees/{Dept}/{action}.aspx" in our case.

Refer the code below,

Download Sourcecode