Introducing the Alloy templates
Episerver CMS comes with a set of ASP.NET MVC demo templates, called Alloy. The Alloy templates contain a site for a fictional company "Alloy Technologies", and the aim is in part to demo the most important features of Episerver and in part to give you a site ready to explore or to start with.
In this topic
- Design philosophy
The Alloy templates are built on the latest Episerver platform. If you are new to Episerver, we recommend that you start by installing an Alloy site and explore it in detail. It will give you a great introduction to the user interface, as well as project structure and programming patterns.
- Based on the latest Episerver CMS
- Built on ASP.NET MVC 5
- Based on the responsive Bootstrap by Twitter HTML framework
The templates are distributed as a Visual Studio extension package. See Installing a sample site.
Since Episerver CMS 7, template development with ASP.NET MVC is supported. The Alloy templates are created as an example of how to build an Episerver site with good characteristics, both in terms of maintainability and performance. They also show an example of how conventions in ASP.NET MVC can be tuned to suit a website like Alloy.
The Alloy templates were initially built after discussions with developers working with ongoing Episerver and MVC development projects. These discussions, prototyping, and the unique characteristics of the Alloy site were distilled into a number of design decisions geared towards making it easy to extend the Alloy site with new content types and functionality. Since then, the templates have been continually updated and extended.
All non-partial views and layouts in the MVC templates use a model of type IPageViewModel<T> where T must be a descendent of PageData. The IPageViewModel interface defines a CurrentPage property as well as a couple of properties geared towards layouts and framework components. This way, all views, including layout files, can rely on some common characteristics of the view model.
To free controllers from having to populate these common properties on the view model, an action filter named PageContextActionFilter is registered globally at startup. This filter inspects the view model which is about to be passed to the view and, given that it is of type IPageViewModel, sets the common properties required by the site’s framework.
Should a specific controller or action want to influence the common properties of the view model, it can do so by populating them on the view model as the filter then will not modify them. Alternatively, a controller can implement an interface named IModifyLayout that tells the filter to pass the Layout property of the view model to the controller after having populated it with default values.
An example of a controller which implements IModifyLayout is the controller for the preview page, PreviewController. It modifies the view model in order to instruct the view to hide the site’s header and footer.
The Alloy templates have a controller named DefaultPageController, which can handle all page types and simply returns a view result with a view location set to /Views/<page_type_name>/Index.cshtml.
This allows us to easily add views for page types by following the above convention for view locations. For page types that require a controller, all we need to do is to create one which is more specific in terms of what page type it handles.
There are different ways to create partial renderers, templates for pages and blocks in content areas and such when using ASP.NET MVC. The three main ways are:
- create a controller,
- create a partial view in the /Views/Shared folder whose name matches the type name of the content type or,
- create a partial view which is registered at startup using a class that implements the IViewTemplateModelRegistrator interface (see the TemplateCoordinator class)
The Alloy templates use the two latter approaches extensively. Partly because the first approach, using a controller, is quite costly in terms of performance, and partly because a controller is not really needed for many of the blocks in Alloy. As a result, the /Views/Shared folder contains a lot of views, which makes it difficult to find a specific one. Therefore, the templates feature a custom view engine, SiteViewEngine, which adds two additional folders in which the partial views for CMS content can be stored – /Views/Shared/PagePartials and /Views/Shared/Blocks.
The Alloy templates feature a customized rendering of content areas.
To support the design requirements for the Alloy website, we implemented a class called AlloyContentAreaRenderer for custom rendering of content areas. See the DependencyResolverInitialization class to see how we make Episerver use our custom renderer for all content areas.
The Alloy templates contain a bonus feature in the form of the ErrorHandlingContentRenderer class. This class is registered as the default type for the IContentRenderer interface during the site’s initialization. It wraps the Episerver CMS default implementation and extends it to provide error handling while rendering partial content.
This has the effect that an exception, of a number of non-critical types, thrown while rendering a block or page in a content area will not crash the entire page. Instead, it will simply hide the failing partial content. If the HTTP request is made by an editor, it will render an error message which can be reported to a developer.
Note that the error handling is only in place if the site is in release mode (debug=”false” in web.config). In debug mode, the request is probably made by a developer and then the standard error handling is used instead, allowing developers to more easily see the error message and stack trace.
Beyond making the site more robust, this functionality also illustrates the flexibility of Episerver CMS API.
The Alloy templates feature a single extension method for the HtmlHelper class named MenuList which is used to build all three navigations components on the Alloy site – the top menu, the sub navigation and the breadcrumbs.
While there are many possible ways to build each of those navigation elements for an MVC site, the MenuList method is especially designed for flexibility through the use of Razor helpers.
The method requires a root page and a Razor helper as argument. It fetches the children of the root page and filter them based on whether they should be visible to the current visitor and whether they should be displayed in navigation or not. Finally, it invokes the Razor helper once for each page.
As Razor helpers are essentially C# code it can be used for many different things, especially since the Razor helpers can recursively invoke themselves.
ASP.NET MVC is designed for testability and flexibility, and Episerver CMS features the abstractions necessary to utilize that. Therefore, almost all communication with the API is kept out of the views and placed in separate classes and, to a lesser extent, in the controllers.
To enable us to switch out components without modifying controllers and to make the code practical to write unit tests for, all dependencies in controllers are injected through their constructors. In ASP.NET MVC, dependencies for controllers and other components are resolved using a DependencyResolver. The templates feature such a class, ServiceLocatorDependencyResolver, which is set as the default dependency resolver through the DependencyResolverInitialization initialization module.
The dependency resolver wraps the IoC container used by the CMS itself, meaning that we do not have to register implementations for the CMS API. Custom classes in the templates generally do not have corresponding interfaces but instead have virtual methods. This means that we do not have to register them while maintaining the ability to write unit tests for code that relies on such types.
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Last updated: Feb 23, 2018