MSDN Magazine - March 2008 - (Page 43)

several best practices that I applied when worka separate object, the Presenter. The Presenter ing on my desktop apps. Two of them were: object then performs any logic necessary to • Separation of concerns: don’t mix UI logic respond to the activity on the view, typically with underlying behavior. by using other objects (the Model) to access • Automated unit testing: write automated databases, perform business logic, and so on. tests that verify whether your code does Once those steps are complete, the Presenter what you think it does. updates the view. This approach gives you testThe underlying principles here apply reability because the presenter is isolated from gardless of technology. Separation of concerns the ASP.NET pipeline; it communicates with is a fundamental principle that exists to help the view through an interface and can be tested you deal with complexity. Mixing Different in isolation from the page. responsibilities within the same object—like MVP works, but the implementation can calculating remaining work hours, formatting be a bit awkward; you need a separate view data, and drawing a graph—is just asking for interface, and you have to write lots of event maintenance problems. And automated testforwarding functions in your codebehind ing is crucial to getting production-quality files. But if you want a testable UI in your Web Figure 1 MVC Pattern Request Flow code while still maintaining your sanity, parForms applications, it’s about the best you’re ticularly when you’re updating an existing project. going to get. Any improvements would require a change in the ASP.NET Web Forms made it very easy to get started, but, in underlying platform. other ways, trying to apply my design principles to Web apps was a struggle. Web Forms are relentlessly UI focused; the fundamen- Model View Controller Pattern tal atom is the page. You start by designing your UI and dragging Luckily, the ASP.NET team has been listening to developers like controls. It’s very seductive to just start slapping your application me and has started development of a new Web application framelogic into the page’s event handlers (much like Visual Basic® en- work that sits side-by-side with the Web Forms you know and love abled for Windows® apps). but has a distinctly different set of design goals: On top of that, unit testing of pages is often difficult. You can’t • Embrace HTTP and HTML—don’t hide it. run a Page object through its lifecycle without spinning up all of • Testability is built-in from the ground up. ASP.NET. While it is possible to test Web apps by sending HTTP • Extensible at almost every point. requests to a server or automating a browser, that kind of testing • Total control over your output. is fragile (change one control ID and the test breaks), hard to set This new framework is based around the Model View Controlup (you have to set up the server on every developer’s machine ex- ler (MVC) pattern, thus the name, ASP.NET MVC. The MVC patactly the same way), and slow to run. tern was originally invented As I started building more sophisticated Web apps, the abstrac- back in the ’70s as part of The MVC pattern divides tions that Web Forms provides, like controls, view state, and the Smalltalk. As I’ll show in your UI into three distinct page lifecycle, started to chafe rather than help. I was spending this article, it actually fits more and more time configuring data binding (and writing tons into the nature of the Web objects: the controller, the of event handlers to get it configured correctly). I had to figure out quite well. MVC divides model, and the view. how to reduce the view state size to get my pages to load faster. Web your UI into three disForms require that a physical file exist at every URL, something tinct objects: the controlthat dynamic sites (like a wiki, for example) make difficult. And ler, which receives and handles input; the model, which contains successfully writing a custom WebControl is a remarkably com- your domain logic; and the view, which generates your output. In plex process that requires a comprehensive understanding of both the context of the Web, the input is an HTTP request, and the repage lifecycle and the Visual Studio® designer. quest flow looks like Figure 1. Since coming to work at Microsoft, I’ve had the opportunity to This is actually quite different from the process in Web Forms. share my learning about various .NET pain points and to hopeful- In the Web Forms model, the input goes into the page (the View), ly alleviate some of that pain. Most recently, such an opportunity and the view is responsible for both handling the input and genarose through my participation as a developer on the patterns & erating the output. When it comes to MVC, on the other hand, the practices Web Client Software Factory project (codeplex.com/websf). responsibilities are separated. In particular, one of the things that patterns & practices builds into So, right now there’s probably one of two things running through its deliverables is automated unit testing. In the Web Client Soft- your head. Either, “Hey, this is great. How do I use it?” or “Why ware Factory, we proposed the use of the Model View Presenter would I write three objects when I only had to write one before?” (MVP) pattern for building testable Web Forms. Both are excellent questions and best explained by looking at an In a nutshell, instead of putting your logic in the page, MVP has example. So I’m going to write a small Web app using the MVC you build your pages so that the page (View) simply makes calls into Framework to demonstrate its advantages. march2008 43 http://codeplex.com/websf

Table of Contents Feed for the Digital Edition of MSDN Magazine - March 2008

MSDN Magazine - March 2008 Contents Toolbox CLR Inside Out Data Points Advanced Basics Office Space Introducing ASP.NET MVC Loosen Up CI Server Performance Office Development Test Run Security Briefs Extreme ASP.NET Foundations .NET Matters {End Bracket}

MSDN Magazine - March 2008

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