Wednesday, January 26, 2011

ASP.NET MVC3 - Creating razor view engine code behind files

While code behind files are generally discouraged for MVC views, there are still times when it's helpful to have strongly typed and pre-compiled code to support a view when you have something more than rudimentary logic involved with view processing.

In order for a single Razor view to have a code-behind file, it must be changed to inherit from another class instead of the default view page class, which is defined in the ~/Views/web.config as
System.Web.Mvc.WebViewPage

The view base class is modified with this addition to the view's markup file:
@inherits <class name>

For example, a code-behind class for ~/Views/Home/Index.cshtml would be
@inherits MySite.Views.Home.Index

If you have a model specified for the view using the @model nugget you must remove it from the view code and apply it to the new base class.

Next, create a new class file for the code-behind class. Following convention, it's probably best to put the file in the same directory as the view file itself and name it similarly. I just grab the view's file name and drop the "html" from the extension. Thus, following our example, we end up with:
~/Views/Home/Index.cs
~/Views/Home/Index.cshtml

The generated class file needs to be modified in these ways:

  • Set the base class to WebViewPage, or WebViewPage<model type> if you had a model type specified in the view code.

  • Add "abstract" to the class definition (a concrete implementation of a WebViewPage derived class must implement the "Execute" method)

Continuing with our example we have a code-behind file for the Home/Index view that looks like this:
namespace MySite.Views.Home
public abstract class Index : WebViewPage
{
// ... my super-duper code goes here
}
}

Now code away! Be sure to expose any methods you want to call from the view code as "protected" or "public" so they are visible to the view's derived class.

Just remember that a view code-behind file is not a substitute for proper separation of concerns. Remember to keep the code you place in a view code-behind class limited to only logic required to make the view do what it needs, no more. Any code that starts to smell of business/application logic should be moved to the appropriate place, either a business library or a controller.

1 comment:

Alfredo Cerritos said...

This works great , Thanks !