MVC Request Life Cycle in Asp.Net

Routing

In MVC request cycle Asp.net Routing is the first step. Fundamentally it is a pattern matching mechanism that matches the request’s URL against the registered URL patterns in the Route Table. When a matching pattern found in the Route Table, the Routing engine forwards the request to the corresponding IRouteHandler for that request. The default one calls the MvcHandler. If the patterns is not found in the Route Table The routing engine returns a 404 HTTP status code against that request.

At first time when application starts, it registers one or more patterns to the Route Table to tell the routing system what to do with any requests that match these patterns. An application has only one Route Table and which is in the Global.asax file of the application. Following is an example

public static void RegisterRoutes(RouteCollection routes)

        {

            routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

            routes.MapHttpRoute(

                name: "DefaultApi",

                routeTemplate: "api/{controller}/{id}",

                defaults: new { id = RouteParameter.Optional }

            );

            routes.MapRoute(

                name: "Default",

                url: "{controller}/{action}/{id}",

                defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }

            );

        }

MVC Handler

MVC handler implements IHttpHandler interface and process the request by using ProcessRequest method as shown below:

protected internal virtual void ProcessRequest(HttpContextBase httpContext)

{

       SecurityUtil.ProcessInApplicationTrust(delegate {

       IController controller;

       IControllerFactory factory;

       this.ProcessRequestInit(httpContext, out controller, out factory);

       try

              {

                     controller.Execute(this.RequestContext);

              }

       finally

              {

                     factory.ReleaseController(controller);

              }

       });

}

Controller

As shown in above code, MvcHandler uses the IControllerFactory instance and tries to get a IController instance. If successful, the Execute method is called. The IControllerFactory could be the default controller factory or a custom factory initialized at the Application_Start event, as shown below:

protected void Application_Start()

{

 AreaRegistration.RegisterAllAreas();

 RegisterRoutes(RouteTable.Routes);

 ControllerBuilder.Current.SetControllerFactory(new CustomControllerFactory());

}

Action Execution

Once the controller has been instantiated, Controller's Action Invoker determines which specific action to invoke on the controller. Action to be execute is chosen based on attributes ActionNameSelectorAttribute (by default method which have the same name as the action is chosen) and ActionMethodSelectorAttribute(If more than one method found, the correct one is chosen with the help of this attribute).

View Result

The action method receives user input, prepares the appropriate response data, and then executes the result by returning a result type. The result type can be ViewResult, RedirectToRouteResult, RedirectResult, ContentResult, JsonResult, FileResult, and EmptyResult.

View Engine

The first step in the execution of the View Result involves the selection of the appropriate View Engine to render the View Result. It is handled by IViewEngine interface of the view engine. By default Asp.Net MVC uses WebForm andRazor view engines. You can also register your own custom view engine to your Asp.Net MVC application as shown below:

protected void Application_Start()

{

 //Remove All View Engine including Webform and Razor

 ViewEngines.Engines.Clear();

 //Register Your Custom View Engine

 ViewEngines.Engines.Add(new CustomViewEngine());

 //Other code is removed for clarity

}

View

Action method may returns a text string,a binary file or a Json formatted data. The most important Action Result is the ViewResult, which renders and returns an HTML page to the browser by using the current view engine