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Understanding MVC Application Execution

Requests to an ASP.NET MVC-based Web application first pass through the UrlRoutingModule object, which is an HTTP module. This module parses the request and performs route selection. The UrlRoutingModule object selects the first route object that matches the current request. (A route object is a class that implements RouteBase, and is typically an instance of the Route class.) If no routes match, the UrlRoutingModule object does nothing and lets the request fall back to the regular ASP.NET or IIS request processing.

From the selected Route object, the UrlRoutingModule object obtains an object that implements the IRouteHandler interface and that is associated with the Route object. Typically, in an MVC application, this will be an instance of the MvcRouteHandler class. The MvcRouteHandler instance creates an MvcHandler object that implements the IHttpHandler interface. The MvcHandler object then selects the controller that will ultimately handle the request. For more information, see ASP.NET Routing.

NoteNote:

When an ASP.NET MVC Web application runs in IIS 7.0, no file name extension is required for MVC projects. However, in IIS 6.0, the handler requires that you map the .mvc file name extension to the ASP.NET ISAPI DLL.

The UrlRoutingModule and MvcRouteHandler classes are the entry points to the ASP.NET MVC framework. They perform the following actions:

  • Select the appropriate controller in an MVC Web application.

  • Obtain a specific controller instance.

  • Call the controller's Execute method.

The following table lists the stages of execution for an MVC Web project.

Stage

Details

Receive first request for the application

In the Global.asax file, Route objects are added to the RouteTable object.

Perform routing

The UrlRoutingModule module uses the first matching Route object in the RouteTable collection to create the RouteData object, which it then uses to create a RequestContext object.

Create MVC request handler

The MvcRouteHandler object creates an instance of the MvcHandler class and passes the RequestContext instance to the handler.

Create controller

The MvcHandler object uses the RequestContext instance to identify the IControllerFactory object (typically an instance of the DefaultControllerFactory class) to create the controller instance with.

Execute controller

The MvcHandler instance calls the controller's Execute method.

Invoke action

For controllers that inherit from the ControllerBase class, the ControllerActionInvoker object that is associated with the controller determines which action method of the controller class to call, and then calls that method.

Execute result

The action method receives user input, prepares the appropriate response data, and then executes the result by returning a result type. The built-in result types that can be executed include the following: ViewResult (which renders a view and is the most-often used result type), RedirectToRouteResult, RedirectResult, ContentResult, JsonResult, FileResult, and EmptyResult.

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