The New ASP.NET Framework
ScottGu gave a demo of the new MVC framework for ASP.NET at the ALT.NET Conference. Here are some notes and thoughts I had after watching ScottHanselman's recording.
The framework should go live in the spring of 2008. The framework is not a replacement for ASP.NET WebForms, but provides an alternative paradigm for building web applications. The new framework still works inside of the ASP.NET runtime - meaning all of the wonderful infrastructure pieces like the configuration system, provider model, SQL cache invalidation, health monitoring, and master pages continue to exist. Like the ASP.NET AJAX extensions – it sounds like we'll only need a new assembly to start the party.
Being an "MVC framework", the software features the Model View Controller pattern. MVC and its many permutations have been (and continue to be) principal patterns in many application frameworks and development environments. There were several mentions of Rails (both the Mono and Ruby types), and at least one reference to Django (the Django book is a good read to get into the framework's mindset).
The framework will provide:
- Mechanisms to enforce a clean separation of concerns
- An API designed for testability
- A pluggable and extensible technology stack
Separation of Concerns
ASP.NET WebForms map an incoming URL to a single .aspx file. Although one can use an HttpModule or VirtualPathProvider to change this behavior, the majority of ASP.NET web applications use this default behavior. In practice, this approach tends to produce code-behind files with intermingled presentation, data access, and business logic. This approach also tightly couples URLs to the physical arrangement of .aspx files in the file system.
The new MVC framework offers a loose coupling between incoming URLs and the view that will ultimately render HTML. ScottGu describes a flexible and pluggable URL dispatching engine that can handle clean and procedural URLs like:
http://OdeToCode.com/articles/show/450
or
http://www.pluralsight.com/classes/register/appliedsilverlight
The URL dispatching engine examines incoming URLs, routes each request to an instance of a controller class, and invokes a method on the controller (the action).
Controllers
Controllers in the new framework support test first and controller first development styles. In other words, you can implement a controller sans any views, and fully test the controller's ability to utilize application logic and services to respond to a request.
The framework provides a low-level interface definition you can implement to claim absolute power over controller policy, but also provides a hierarchy of concrete controller classes to build upon.
When the controller is ready, it can call RenderView(string viewName, object viewData) to generate the appropriate user interface response. Thanks to generics, this boundary can also be strongly typed.
Views
Views render HTML, but views are not web forms - there is no page lifecycle, postbacks, or viewstate in this framework.
In general, views are simple templates. Templates are concerned only with presentation. To enforce a separation of concerns, many template engines do not allow a template to change the value of a variable or call into application logic, but the ASP.NET framework will allow code blocks and data-binding. The view never references a controller, and the controller never references a view - so testability and a separation of concerns prevail.
Designed For Testability
One of the current difficulties in writing unit tests for code running inside an ASP.NET environment is the pervasiveness of sealed classes like HttpContext.The MVC framework features an interface based API with IHttpContext, IResponse, IRequest, etc.
There is a mock view engine and, I believe, mock implementations of IHttpContext and the like to make testing easier.
At the beginning of the discussion Scott mentioned that the framework will include inversion of control containers, although I don't recall this feature appearing in the presentation.
A Pluggable Architecture
It sounds as if every major service in the MVC framework is pluggable – the view engine (throw in Brail), the dependency injection framework (throw in Structure Map), the URL dispatcher, the controllers, and more.
Look For the CTP Soon
The new framework appears to marry mature paradigms from outside the world of ASP.NET with the high performance and robust infrastructure of the ASP.NET runtime. Look for a CTP by the end of the year.