Question

I need to do routing in an existing asp.net app – not an asp.net mvc (yeah I know I should convert but let’s say it’s not possible right now so don’t tell me 🙂 ) – how can I do routing to a normal class instead of an aspx page as all sample code I see is always with aspx page like here:

http://msdn.microsoft.com/en-us/magazine/dd347546.aspx

To precise, I want to do a bit like in MVC Controller routing : the controller for example product is a pure class you access through http://domain.com/product

Answer 1

ASP.NET MVC and ASP.NET Web Forms share the same routing infrastructure in that both frameworks ultimately need to come up with an IHttpHandler to handle the HTTP request:

The IHttpHandler interface has been a part of ASP.NET since the
beginning, and a Web Form (a System.Web.UI.Page) is an IHttpHandler.

(From the MSDN article linked in the question)

In ASP.NET MVC the System.Web.Mvc.MvcHandler class is used, which then delegates to a controller for further handling of the request. In ASP.NET Web Forms usually the System.Web.UI.Page class that represents an .aspx file is used, but a pure IHttpHandler associated with .ashx file can also be used.

So you can route to an .ashx handler as an alternative to an .aspx Web Forms page. Both implement IHttpHandler (as does MvcHandler), but with the former that’s all it does. And that’s as close as you can get to a ‘pure class’ handling a (routed) request. And since the handler part is just an interface, you are free to inherit from your own class.

<%@ WebHandler Language="C#" Class="LightweightHandler" %>

using System.Web;

public class LightweightHandler : YourBaseClass, IHttpHandler
{
  public void ProcessRequest(HttpContext context)
  {
    context.Response.ContentType = "text/plain";
    context.Response.Write("Hello world!");
  }

  public bool IsReusable { get { return false; } }
}

Notice that an IRouteHandler just needs to return an instance of IHttpHandler:

public IHttpHandler GetHttpHandler(RequestContext requestContext);

You may need to jump through some hoops to instantiate your handler using the BuildManager* if you use .ashx files. If not, you can just new up an instance of your class and return it:

public IHttpHandler GetHttpHandler(RequestContext requestContext)
{
  // In case of an .ashx file, otherwise just new up an instance of a class here
  IHttpHandler handler = 
    BuildManager.CreateInstanceFromVirtualPath(path, typeof(IHttpHandler)) as IHttpHandler;

  // Cast to your base class in order to make it work for you
  YourBaseClass instance = handler as YourBaseClass;
  instance.Setting = 42;
  instance.DoWork();

  // But return it as an IHttpHandler still, as it needs to do ProcessRequest
  return handler;
}

See the answers to this question for much more in-depth analysis of routing pure IHttpHandlers: Can ASP.NET Routing be used to create “clean” URLs for .ashx (IHttpHander) handlers?

**I’m not entirely sure about the BuildManager example, someone please correct me if I got that part wrong*