Excerpt from ASP.NET MVC Framework Unleashed [con't]
What Is ASP.NET MVC?
The Microsoft ASP.NET MVC framework is Microsoft’s newest framework for building web applications. The ASP.NET MVC framework was designed from the ground up to make it easier to build good software in the sense of good software discussed in this chapter.
The ASP.NET MVC framework was created to support pattern-based software development. In other words, the framework was designed to make it easier to implement software design principles and patterns when building web applications.
Furthermore, the ASP.NET MVC framework was designed to its core to support unit tests. Web applications written with the ASP.NET MVC framework are highly testable.
ASP.NET MVC Is Part of the ASP.NET Framework
Microsoft’s framework for building software applications—any type of application including desktop, web, and console applications—is called the .NET framework. The .NET framework consists of a vast set of classes, tens of thousands of classes, which you can use when building any type of software application. For example, the .NET framework includes classes for working with the file system, accessing a database, using regular expressions, and generating images.
The ASP.NET framework is one part of the .NET framework. The ASP.NET framework is Microsoft’s framework for building web applications. It contains a set of classes that were created specifically to support building web applications. For example, the ASP.NET framework includes classes for implementing web page caching, authentication, and authorization.
Microsoft has two frameworks for building web applications built on top of the ASP.NET framework: ASP.NET Web Forms and ASP.NET MVC (see Figure 1.1).
ASP.NET MVC is an alternative to, but not a replacement for, ASP.NET Web Forms. Some developers find the style of programming represented by ASP.NET Web Forms more compelling, and some developers find ASP.NET MVC more compelling. Microsoft continues to make heavy investments in both technologies.
The Origins of MVC
The ASP.NET MVC framework is new; however, the MVC software design pattern itself has a long history. The MVC pattern was invented by Trygve Reenskaug while he was a visiting scientist at the Smalltalk group at the famed Xerox Palo Alto Research Center. He wrote his first paper on MVC in 1978. He originally called it the Thing Model View Editor pattern, but he quickly changed the name of the pattern to the Model View Controller pattern.
The MVC pattern was first implemented as part of the Smalltalk-80 class library. It was originally used as an architectural pattern for creating graphical user interfaces (GUIs).
The meaning of MVC shifted radically when the pattern was adapted to work with web applications. In the context of web applications, the MVC pattern is sometimes referred to as the Model 2 MVC pattern.
The MVC pattern has proven to be very successful. Today, the MVC pattern is used by several popular web application frameworks including Ruby on Rails, Merb, and Django. The MVC pattern is also popular in the Java world. In the Java world, MVC is used in the Struts, Spring, and Tapestry frameworks.
The first major MVC framework for ASP.NET was the open source MonoRail project (see CastleProject.org). There continues to be an active developer community around this project.
The Microsoft ASP.NET MVC framework was originally created by Scott Guthrie on an airplane trip to Austin, Texas, to speak at the first Alt.NET conference in October 2007. (Scott Guthrie was one of the creators of ASP.NET.) Scott Guthrie’s talk generated so much excitement that the ASP.NET MVC framework became an official Microsoft product. ASP.NET MVC 1.0 was released in the first part of 2009.
The Architecture of an ASP.NET MVC Application
An MVC application, a Model View Controller application, is divided into the following three parts:
Model—An MVC model contains all of an application’s logic that is not contained in a view or controller. The model includes all of an application’s validation logic, business logic, and data access logic. The MVC model contains model classes that model objects in the application’s domain.
View—An MVC view contains HTML markup and view logic.
Controller—An MVC controller contains control-flow logic. An MVC controller interacts with MVC models and views to control the flow of application execution.
Enforcing this separation of concerns among models, views, and controllers has proven to be a useful way of structuring a web application.
First, sharply separating views from the remainder of a web application enables you to redesign the appearance of your application without touching any of the core logic. A web page designer (the person who wears the black beret) can modify the views independently of the software engineers who build the business and data access logic. People with different skills and roles can modify different parts of the application without stepping on each other’s toes.
Furthermore, separating the views from the remainder of your application logic enables you to easily change the view technology in the future. One fine day, you might decide to re-implement the views in your application using Silverlight instead of HTML. If you entangle your view logic with the rest of your application logic, migrating to a new view technology will be difficult.
Separating controller logic from the remainder of your application logic has also proven to be a useful pattern for building web applications. You often need to modify the way that a user interacts with your application. You don’t want to touch your view logic or model logic when modifying the flow of execution of your application.
Understanding the Sample ASP.NET MVC Application
A good way to get a firmer grasp on the three logical parts of an MVC application is to take a look at the sample application that is created automatically when you create a new ASP.NET MVC project with Visual Studio.
Follow these steps:
Launch Visual Studio.
Select the menu option File, New Project.
In the New Project dialog, select your favorite programming language (C# or VB.NET) and select the ASP.NET MVC Web Application template. Give your project the name MyFirstMvcApp and click the OK button (see Figure 1.2).
Immediately after you click the OK button to create a new ASP.NET MVC project, you see the Create Unit Test Project dialog in Figure 1.3. Leave the default option selected—Yes, Create a Unit Test Project—and click the OK button.
Your computer hard drive will churn for a few seconds while Visual Studio creates the default files for a new ASP.NET MVC project. After all the files are created, the Solution Explorer window should contain the files in Figure 1.4.
The Solution Explorer window in Figure 1.4 contains two separate projects: the ASP.NET MVC project and the Test project. The Test project contains all the unit tests for your application.
ASP.NET MVC Folder Conventions
The ASP.NET MVC framework emphasizes convention over configuration. There are standard locations for each type of file in an ASP.NET MVC project. The ASP.NET MVC application project contains the following folders:
App_Data—Contains database files. For example, the App_Data folder might contain a local instance of a SQL Server Express database.
Content—Contains static content such as images and Cascading Style Sheet files.
Controllers—Contains ASP.NET MVC controller classes.
Models—Contains ASP.NET MVC model classes.
Views—Contains ASP.NET MVC views.
Running the Sample ASP.NET MVC Application
When you create a new ASP.NET MVC application, you get a simple sample application. You can run this sample application by selecting the menu option Debug, Start Debugging (or press the F5 key).
The first time that you run a new ASP.NET MVC application in Visual Studio, you receive a dialog asking if you want to enable debugging. Simply click the OK button.
When you run the application, your browser opens with the page in Figure 1.5.
You can use the tabs that appear at the top of the page to navigate to either the Home or the About page. You also can click the Login link to register or log in to the application. And, that is all you can do with the application.
This sample application is implemented with one ASP.NET MVC controller and two ASP.NET MVC views. The sample application does not contain any business or data access logic, so it does not contain any ASP.NET MVC model classes.
The controller is located in the Controllers folder:
If you open the HomeController in the Code Editor window, you see the file in Listing 1.1.
Listing 1.1 Controllers\HomeController.cs (C#)
Listing 1.1 Controllers\HomeController.vb (VB)
The file in Listing 1.1 contains a class with two methods named Index() and About(). Methods exposed by a controller are called actions. Both the Index() and About() actions return a view.
When you first run the sample application, the Index() action is invoked and this action returns the Index view. If you click the About tab, the About() action is invoked and this action returns the About view.
The two views can be found in the Views folder at the following location:
The content of the Index view is contained in Listing 1.2.
Listing 1.2 Views\Home\Index.aspx (C#)
Listing 1.2 Views\Home\Index.aspx (VB)
Notice that a view consists mostly of standard HTML content. For example, the view contains standard <h2> and <p> tags. A view generates a page that is sent to the browser.
The goal of this chapter was to provide you with an overview of the ASP.NET MVC framework. The first part of this chapter was devoted to a discussion of a definition of good software. You were provided with a brief introduction to software design principles and patterns and the importance of unit tests. You learned how software design principles and patterns and unit tests enable you to create software that is resilient to change.
Next, you were provided with an introduction to the Model View Controller software design pattern. You learned about the history and benefits of this pattern. You learned how the ASP.NET MVC framework implements the Model View Controller pattern and how ASP.NET MVC enables you to perform pattern-based software development.
Finally, we explored the sample ASP.NET MVC application that is created when you create a new ASP.NET MVC project. We took our first look at an ASP.NET MVC controller and an ASP.NET MVC view.
Excerpt from ASP.NET MVC Framework Unleashed.
|By Stephen Walther
Published by Sams
© Copyright Pearson Education. All rights reserved.
Original: August 4, 2009