ASP.NET MVC Overview

Model-View-Controller is an architectural pattern used to separate an application into three main aspects:

Model: The model represents and manipulates data of the application. It responds to the request from the view and it also responds to instructions from the controller to update itself. A class or set of classes that describe data and responsible for maintaining data.

View: The view represents an interface to show to the user. Typically, this interface is rendered from the model data triggered by a controller decision. Also view handles requests from user and informs controller.

Controller: The controller is responsible for responding to user input, performs interactions on the data model objects and ultimately selects a view to render.

              

The ASP.NET MVC Framework implements the MVC pattern that’s suitable for web applications.

The main advantages of ASP.Net MVC are:

• Full control over the rendered HTML.
• Clean separation of concerns.
• Test Driven Development (TDD).
• Powerful routing system.
• Built in ASP.Net platform.
• No View State/Post Back event and Page life Cycle.

Visual Studio MVC Project

We can create visual studio MVC project with Empty, Internet Application or Intranet Application templates. Empty template creates a relatively small number of files and directories, and gives us just the minimum structure on which to build. The Internet Application and Intranet Application templates fill out the project to give a more complete starting point, using different authentication mechanisms that are suited to Internet and intranet applications.

ASP.NET MVC project structure: Project structure of MVC is almost similar for all templates. See table below for details:

 Table 1: MVC 3 Project Items

File or Folder	Description
Content	Put static content like images and CSS.
Controllers	Put controller classes
Models	Put model classes
Scripts	Put script libraries
Views	Put views and partial views
Views/Shared	Put layouts and shared views
Global.asax	Global ASP.NET application class use to register routing, set up any code to run on application initialization or to  handle unhandled exceptions etc.
Web.config	Configuration files of application.
App_Data	Use to put data, such as XML files or DB files etc.
bin	Assembly of MVC application and other referenced assemblies.

Routing: The ASP.NET Routing module is responsible for mapping incoming browser requests to particular MVC controller actions. By default routes defined in “Global.asax” file method named “RegisterRoutes”. Method “RegisterRoutes” get called by “Application_Start” method when the application is first started.

Default snippet:

using System.Web.Routing;

public static void RegisterRoutes(RouteCollection routes)

        {

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

            routes.MapRoute(

                "Default", // Route name

                "{controller}/{action}/{id}", // URL with parameters

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

            );

        }

protected void Application_Start()

        {

            RegisterRoutes(RouteTable.Routes);

        }

The parameter to “RegisterRoutes” method is the value of the static “RouteTable.Routes” property, which is an instance of the RouteCollection class.

URL Patterns: Each route contains a URL pattern. If the pattern matches the URL, then it is used by the routing system to process that URL. By default MVC application create a default route as below.

routes.MapRoute(

                "Default", // The name of the route to map.

                "{controller}/{action}/{id}", // The URL pattern for the route.

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

// An object that contains default route values.

              );

URL patterns will match only URLs with the specified number of segments. A default value is applied when the URL doesn’t contain a segment that can be matched to the value.

Here URL pattern is "{controller}/{action}/{id}", where pattern have 3 segment with default value. First segment maps to controller second with action and third one with id which is optional. Below is the table to show how a URL will map to pattern.

Table 2 : URL Mapping

Number of         Segments	URLs	Segment variables
0	http://mvc-demo.com/	Map to default value:     Controller = "Home", Action = "Index"
1	http://mvc-demo.com/Home	Controller = "Home", Action = "Index"
2	http://mvc-demo.com/Home/Index	Controller = "Home", Action = "Index"
3	http://mvc-demo.com/Home/Index/Hi	Controller = "Home", Action = "Index" , Id= “Hi”
4	http://mvc-demo.com/Home/Index/Hi/XX	No match—too many segments
2	http://mvc-demo.com/Account/LogOn	Controller = "Account", Action = "LogOn"
2	http://mvc-demo.com/Account/Profile	Controller = " Account ", Action = "Profile"

Static URL Segments: We can also create patterns that have static segments. Suppose we want to create URLs that are prefixed with Classic:

http:// mvc-demo.com /Classic/Home/Index

We can do so by using a pattern like

routes.MapRoute("Classic", "Classic/{controller}/{action}/{id}",

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

            );

Route Ordering: The MapRoute method adds a route to the end of the route collection, which means that routes are generally applied in the order in which we add them. The route system tries to match an incoming URL against the URL pattern of the route that was defined first, and proceeds to the next route only if there is no match. The routes are tried in sequence until a match is found or the set of routes has been exhausted.

Note: As practice we must define more specific routes first and generic/default routes later.

Accessing a Custom Segment Variable in an Action Method:

 RouteData.Values["id"]  Or Action method Parameters

Defining Variable-Length Routes:

A URL pattern is to accept a variable number of segments.

routes.MapRoute("CatchAll", "{controller}/{action}/{id}/{*catchall}",

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

            );

The first three segments are used to set values for the controller, action, and id variables, respectively. If the URL contains additional segments, they are all assigned to the catchall variable. There is no upper limit to the number of segments that the URL pattern in this route will match.

Example: http://mvc-demo.com/Home/Index/100/ABC/XYZ

Here controller = Home, Action = Index, id = 100, catchall = ABC/XYZ

Prioritizing Controllers by Namespaces:

If we have two controllers with same name in different namespaces and an incoming URL matches a route.Whenever this naming clash happens, an error is reported because MVC Framework doesn’t know what to do. To resolve this clash we can give preference to certain namespaces.

routes.MapRoute("CatchAll", "{controller}/{action}/{id}",

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

new[] { "MVCDemo.Controllers"}

            );

The namespaces added to a route are given equal priority. If we want to give preference to a single controller in one namespace, but have all other controllers resolved in another namespace, we need to create multiple routes.

 Constraining Routes:

Using a Regular Expression:

routes.MapRoute("CatchAll", "{controller}/{action}/{id}",

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

new { controller = "^H.*" },

new[] { "MVCDemo.Controllers"}

            );

In this example, we have used a constraint with a regular expression that matches URLs only where the value of the controller variable begins with the letter H.

Route to a Set of Specific Values:

routes.MapRoute("CatchAll", "{controller}/{action}/{id}",

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

new { controller = "^H.*", action="^Index$|^About$" },

new[] { "MVCDemo.Controllers"}

            );

Here URLs will match only when the controller variable begins with the letter H and the action variable is Index or About

Route Using HTTP Methods:

routes.MapRoute("CatchAll", "{controller}/{action}/{id}",

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

new { controller = "^H.*", action="Index|About", httpMethod = new HttpMethodConstraint("GET")},

new[] { "MVCDemo.Controllers"}

            );

Bypassing the Routing System:

Prevent URLs, from being evaluated against our routes. We do this by using the IgnoreRoute method of the RouteCollection class.

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

If the URL pattern passed to the IgnoreRoute method matches, then no subsequent routes will be evaluated.

Generating Outgoing URLs:    There is number of ways to create outgoing URLs in views and controller actions.

Generate URLs in View:

Html.ActionLink:
The straight forward way to generate an URL is to use ActionLink method of the HtmlHelper class. The ActionLink method generates an anchor element that contains the virtual path of the specified action. There are many overloaded versions of ActionLink method. Important parameters of ActionLink are:

• linkText : The inner text of the anchor element.
• actionName : The name of the action.
• controllerName : The name of the controller.
• routeValues : An object that contains the parameters for a route. If value provided in routeValues does not correspond with a route parameter then values appended to the outgoing URL as the query string
• htmlAttributes : An object that contains the HTML attributes to set for the element. The “class” is a keyword that’s need to prefix with the “@” character.

@Html.ActionLink("Home", "Index", "Home", new { id = 100,para1=hi }, new { @class="clsLink"})

Html Output : <a href="/Home/Index/100?para1=hi">Home</a>

Url.Action:

The Url.Action method works in the same way as the Html.ActionLink method, except that it generates only the URL not anchor tag.

URL is: @Url.Action("Index ", " Home ", new { id = 100))

Html.RouteLink:

            Another way to generate URLs is to use the route name or route values.

@Html.RouteLink("Home", new { controller = "Home", action = "Index" })

Html.RouteUrl:

The “UrlHelper.RouteUrl()” method returns an URL as a string based on the route name or route values.

Generate URLs in Action Methods:

To generate a URL, same URL helper methods can use in the action method like Url.Action and Url. RouteUrl.

RedirectToAction : Its used to call another action method using GET request

return RedirectToAction("About", "Home");

The method works the same way as the “HtmlHelper.ActionLink()” or “UrlHelper.Action()“.

The “RedirectToAction()” method is used to return an object of “RedirectToRouteResult“.

RedirectToRoute:

return RedirectToRoute("Default", new { controller = "Home", action = "About", id = "MyID" });

The method works the same way as the “HtmlHelper.RouteLink()” or “UrlHelper.RouteUrl()“.

The “RedirectToRoute()” method is used to return an object of “RedirectToRouteResult“.

Areas:

ASP.Net MVC Framework support to use areas to break up the application into sub-applications.
Each area represent a functional segment of the application. Area is very useful for large project. In area we can manage separate set of resources  like Model/View/Controller based on segment/sub-applications/module. Area also helps developers to work together without colliding with one another work.

Area can be created in project after right click on project file and select area. area contain a mini project with model/view/controller folder with a area registration class file. For example if we create a area  Admin than one file AdminAreaRegistration will create to manage route of the area. Method RegisterArea use to declare area route. This method get called once application start using "global.asax" file.

public class AdminAreaRegistration : AreaRegistration
    {
        public override string AreaName
        {
            get
            {
                return "Admin";
            }
        }

        public override void RegisterArea(AreaRegistrationContext context)
        {
            Routes.RegisterRoutes(context);
        }
    }

protected void Application_Start()
{
//This call RegisterArea methods of all class which derived from AreaRegistration class
AreaRegistration.RegisterAllAreas();

}

Area Route: Area route works same as normal route here we can use area as part of URL.
Example :  @Html.ActionLink("Admin Area", "Index",new { area= "Admin" })

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