ASP.NET MVC Framework

Prerequisites

A brief Introduction to the ASP.NET MVC Framework by Scott Guthrie:

• ASP.NET MVC Framework
• ASP.NET MVC Framework (Part 1)
• ASP.NET MVC Framework (Part 2): URL Routing
• ASP.NET MVC Framework (Part 3): Passing ViewData from Controllers to Views

An excellent Screencast by Scott Hanselman.

Overview

The MVC (Model-View-Controller) is a popular pattern to develop UI-centric applications based on a simple concept: divide the implementation into three logical components:

• Model,
• View,
• Controller.

The ASP.NET MVC Framework is an implementation of the MVC pattern, and has built-in support for developing web applications. Let's take a quick look at these three components.

Figure 1: The MVC Framework

• Model: Refers to the domain logic of your application. Usually the state of the Model is persisted in the database. Consider it as the middle tier in a typical n-Tier application, which consist of the business logic and domain objects.
• View: Is typically the User Interface, which is used to show the Model data and take input from the User.
• Controller: Is responsible for handling the user interaction. This is the Ultimate Driver of the whole ASP.NET MVC Framework. Depending upon the User gesture it decides which action to perform on the model; it also builds the view data and finally decides which View to render.

The ASP.NET MVC Framework is an alternate and better way to develop web applications, comparing to the regular web form model. It provides us with:

• Clean Separation of Concerns, where each component is serving only one purpose. Thus it also gives us the opportunity to integrate TDD (Test-Driven Development) in the development workflow and unit test each component without considering the others, as most of the framework components are interface-based. This allows us to mock them out.
• The whole framework is very much extensible and pluggable. It is really easy to replace or customize each part without affecting the others.
• Pretty/SEO (Search Engine Optimization) URLs. Full controls of how URLs are constructed. No need to do URL Rewriting anymore.
• True stateless model of the web. We no longer have to deal with postbacks and ViewState.
• Full control of the generated HTML. This means no more naming containers.
• Utilize the existing knowledge of ASP.NET like Providers, Caching, Configuration and so on.

Request Flow

In regular ASP.NET web form applications, URLs are usually mapped to physical disk files. When a URL is requested, the code of the associated file gets executed, which generates the HTML. However, in the ASP.NET MVC Framework the URLs are tied with the Controllers rather than the disk file. The component that is responsible to map the URL with the Controller is the Routing Handler. When the application starts, it is required to register the URL Routing Rules, which the Routing Handler uses to map the controller when the request arrives. Let's take a quick view of how a request is carried in different layers of the ASP.NET MVC Framework:

Figure 2: The Request Flow

• The user requests a URL.
• The ASP.NET MVC Framework evaluates the requested URL against the registered Routing Rules and finds a matching Controller. The Framework forwards the request to the matching Controller.
• The Controller calls the Model to build ViewData. It can call the model multiple times depending upon the ViewData that it is building.
• The Model, as mentioned earlier, is the middle tier, which might involve data access components, workflow activities, external web service dependencies etc. The Model returns the requested data to Controller.
• The Controller selects a View and passes the data to the View which it previously got from the Model. The View Renders the data and returns the generated HTML to the User.