Select templates

7 min

The resulting rendering template for a requested content instance is selected based on page or partial renderers, tags, and active display channels.

📘 Note The examples are based on MVC.

A page or a block can have multiple associated templates; for example, one for a web channel and one for a mobile device. Pages can also have a partial template used when you display the page inside the content area of another page. See Render contentRender content and TemplateDescriptor and tags.

If you register multiple templates, the TemplateResolver service selects the resulting rendering template using an algorithm based on content model, template types, rendering mode (page or partial rendering), tags, and inheritance. If needed, you can use events to override the TemplateResolver selection.

selectingtemplates.png

A default TemplateResolver implementation selects templates based on the procedure below.

The EPiServer.Web.TemplateResolver.TemplateResolving event is raised. If an event handler selects a template, it uses it without further handling.

It filters templates matching the desired content type according to the rendering mode: If it is a page, it selects a suitable controller; if it is partial rendering, it selects a suitable partial controller or partial view. For partial templates, it filters the list according to the main template.

If it requests the template with a specific tag, it filters the list on that tag. If no template matching the tag exists, it considers templates from Step 2.

If any display channel is active, and template tags match that channel, it filters templates for DisplayChannel.

From remaining templates, the shortest inheritance chain to the TemplateModel marked as Default and not inherited, is selected.

If there is no match from Step 5, the shortest inheritance chain to TemplateModel that is marked as Default, is selected.

If there is no match from Step 6, the shortest inheritance chain to TemplateModel, is selected.

The EPiServer.Web.TemplateResolver.TemplateResolved event is raised, providing a chance to replace the selected template.

📘 Note The shortest inheritance chain means that a template that is registered directly for the content model type is preferred before a template registered for a base class or interface. For interfaces, the length of the inheritance chain is defined by following the inheritance chain upwards to see where the interface is implemented.

Examples

The following examples assume you have a content model and use multiple rendering templates for different display channels. See ContentContent, Render contentRender content, and Display channelsDisplay channels for information.

Select page rendering

The template selected to render a content instance depends on the context, such as channel and tagging. To automatically register a template for rendering, it must implement EPiServer.Web.IRenderTemplate<T> (where T states which model it can render). If you use a base class like PageController<T> or BlockComponent<T>you do not need to implement the interface explicitly for your templates. In addition, you can use the TemplateDescriptorAttribute to specify more details about the template, such as tags and inheritance. See TemplateDescriptor and tags.

Example: A content type model.

[ContentType]
public class MyPage: PageData {
  public virtual string Heading {
    get;
    set;
  }
  public virtual string MainIntro {
    get;
    set;
  }
  public virtual XhtmlString MainBody {
    get;
    set;
  }
}

Given that there are templates defined as follows:

public partial class MyPageTemplate : TemplatePage<MyPage> { }

[TemplateDescriptor(Tags = new string[] { RenderingTags.Mobile })]
public partial class MyPageMobileTemplate : TemplatePage<MyPage> { }

[TemplateDescriptor(Inherited = true)]
public partial class MyFallbackTemplate : TemplatePage<PageData> { }

public partial class MyPageTeaser : ContentControllerBase<MyPage> { }

[TemplateDescriptor(Inherited = true)]
public partial class PageTeaser : ContentControllerBase<PageData> { }

You register the above templates as templates for MyPage. You can register a template for a base type and an interface (MyFallbackController and PageTeaser in the code sample), which you register for PageData, not the specific type). If you want the template to be available for all subtypes, for example, if you want to have a fallback template for content types without a specific template, set Inherited=true for the TemplateDescriptor attribute.

For the example above, a browser request for a page of the type MyPage will result in the following:

If no DisplayChannel is active, the MyPageTemplate template is selected because no tag is active (disqualifies MyPageMobileTemplate), and MyPageTemplate has shorter inheritance chain than MyFallbackTemplate. MyPageTeaser and PageTeaser are partial renderers and are filtered away.

If a DisplayChannel named Mobile is active, it selects the MyPageMobileTemplate template, because it prefers templates with a tag matching active channels.

Select block rendering

Blocks can be either a property on a page or a shared block instance in a content area. The selection of a template for a block is similar to the selection of a page template, except that you can only render blocks in the context of a page template. Render blocks using partial views or view components. When rendering a block in a page template, you can use tags to define how you should render the block.

Example: Templates defined for a MyBlock block type.

[ContentType]
public class MyBlock : BlockData {}

[TemplateDescriptor(Default = true)]
public partial class MyBlockTemplate : BlockContoller<MyBlock> {}

[TemplateDescriptor(Tags = new string[] {"Mobile"})]
public partial class MyBlockMobileTemplate : BlockContoller<MyBlock> {}

You can also use a tag to define rendering in a specific area, such as a Sidebar in a page template:

@Html.PropertyFor(x=>x.MyBlock, new {tag = "SideBar"})

See TemplateDescriptor and tags for information on how to apply tags.

Block layout in a content area

If you specify a tag for a content area, then content added to that area will use a template matching that tag. You can use display options to let editors define the layout of a block in a content area from edit view. See Display optionsDisplay options.