ASP.NET MVC Controller and Actions

Controllers are classes which are responsible for processing incoming requests, performing operations on the domain model, and selecting views to render to the user.

Controller classes must implement the IController interface from the

System.Web.Mvc namespace.

public interface IController {

void Execute(RequestContext requestContext);

}

The base class for all controllers is the ControllerBase class, which provides general MVC handling. The Controller class inherits from ControllerBase and is the default implement of a controller. The Controller class is responsible for the following processing stages:

Locating the appropriate action method to call and validating that it can be called.

Getting the values to use as the action method's arguments.

Handling all errors that might occur during the execution of the action method.

Providing the default WebFormViewEngine class for rendering ASP.NET page types (views).

All controller classes must be named by using the "Controller" suffix.

Main features of controller:

• Action methods: Action method is exposed on a different URL and is invoked with parameters extracted from the incoming request.

• Action results: Action methods return an instance of a class that derives from ActionResult. The ActionResult class is the base for all action results.

• Filters: You can encapsulate reusable behaviors as filters, and then tag each behavior onto one or more controllers or action methods by putting an [Attribute] in your source code.

  

Actions Methods: Action method typically map with user interaction.  When user requests a URL, the MVC use the route to determine controller and action method to handle the request. Most action method returns an instance of ActionResult.

Receiving Input: Controllers access incoming data, such as query string values, form values, and parameters parsed from the incoming URL by the routing system.

Commonly Used Context Objects use to get data are:

Property	Type	Description
Request.QueryString	NameValueCollection	GET variables sent with this request
Request.Form	NameValueCollection	POST variables sent with this request
Request.Cookies	HttpCookieCollection	Cookies sent by the browser with this
Request.HttpMethod	string	The HTTP method (verb, such as GET or POST) used for this request
Request.Headers	NameValueCollection	The full set of HTTP headers sent with this request.
Request.Url	Uri	The URL requested
Request.UserHostAddress	string	The IP address of the user making this
RouteData.Route	RouteBase	The chosen RouteTable.Routes entry for this request
RouteData.Values	RouteValueDictionary	Active route parameters (either extracted from the URL or default values)
HttpContext.Application	HttpApplicationStateBase	Application state store
HttpContext.Cache	Cache	Application cache store
HttpContext.Items	IDictionary	State store for the current request
HttpContext.Session	HttpSessionStateBase	State store for the visitor’s session
User	IPrincipal	Authentication information about the logged-in user
TempData	TempDataDictionary	Temporary data items stored for the current user

Action Methods Parameters:

• Value-type parameters are compulsory. To make them optional, either specify a default value or change the parameter type to a nullable type, so the MVC Framework can pass null if no value is available.

• Reference-type parameters are optional. To make them compulsory (to ensure that a non-null value is passed), add some code to the top of the action method to reject null values.

ActionResult Return Type: ActionResult class is the base for all action results. However, there are different action result types, depending on the task that the action method is performing. The most common action is to call the View method. The View method returns an instance of the ViewResult class, which is derived from ActionResult.

The following table shows the built-in action result types and the action helper methods that return them.

Action Result	Helper Method	Description
ViewResult	View	Renders a view as a Web page.
PartialViewResult	PartialView	Renders a partial view, which defines a section of a view that can be rendered inside another view.
RedirectResult	Redirect	Redirects to another action method by using its URL.
RedirectToRouteResult	RedirectToAction RedirectToRoute	Redirects to another action method.
ContentResult	Content	Returns a user-defined content type.
JsonResult	Json	Returns a serialized JSON object.
JavaScriptResult	JavaScript	Returns a script that can be executed on the client.
FileResult	File	Returns binary output to write to the response.
EmptyResult	(None)	Represents a return value that is used if the action method must return a null result (void).

Examples:

public ViewResult Index()

        {

            ViewBag.CurrentDate = DateTime.Now;

            ViewData["Message"] = "Hello";

            var model = new IndexModel()

            return View(model);

        }

        public ContentResult Index(string contentType)

        {

            switch (contentType)

            {

                case "plain" :

                    return Content("This is plain text", "text/plain", Encoding.Default);

                    break;

                case "xml":

                     XElement data = new XElement("Emp", new XAttribute("firstname", e.Title), new XAttribute("lastname", e.Description));

                     return Content(data.ToString(), "text/xml");

                    break;

                default:

                    return Content("This is plain text", "text/plain", Encoding.Default);

                    break;

            }

        }

     

        public JsonResult JsonData()

        {

            var model = new IndexModel()

            return Json(model);

        }

        public FileResult AnnualReport()

        {

            string filename = @"c:\Report.pdf";

            string contentType = "application/pdf";

            string downloadName = "Report2013.pdf";

            return File(filename, contentType, downloadName);

        }

        public FileStreamResult DownloadReport(){

            Stream stream = "...stream...";

            return File(stream, "text/html");

        }

        public HttpStatusCodeResult StatusCode()

        {

            return new HttpStatusCodeResult(404, "URL cannot be serviced");

        }

Other Posts: MVC3 Overview | Filters