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Preview rendering for blocks

This topic describes how to create a view and controller for previewing blocks in Optimizely.

The preview adds on-page editing functionality, and a realistic view of what the block will look like when added to content areas with different widths.

How it works

Shared blocks are rendered in the context of a page, such as inside a content area. Like pages, you can edit blocks in the All Properties view, but to preview and edit block in the On-Page Editing view, you can create a preview page used to render blocks in edit view. A block template is typically a partial template like a view component, or a partial view. The rendering is using the built-in Preview tag in the EPiServer.Framework.Web namespace.

Creating a block preview template

The following example creates these components to build a preview that you can use for all blocks:

  • A block preview model
  • A preview controller
  • A preview view

See Content templates and Content types for information on how to create page types, controllers and views.

Block preview model

Example: The block preview model with a content area.

📘

Note

The PageViewModel is a pattern from the Alloy sample site and is not required if the site is not based on Alloy.

namespace AlloyTemplates.Models.ViewModels
    {
      public class PreviewModel : PageViewModel<SitePageData>
      {
        public PreviewModel(SitePageData currentPage, IContent previewContent)
        : base(currentPage)
        {
          PreviewContentArea = new ContentArea();
          PreviewContentArea.Items.Add(new ContentAreaItem
          {
            ContentLink = previewContent.ContentLink
          });
        }
    
        public ContentArea PreviewContentArea { get; set; }
      }
    }

Preview controller

PreviewController inherits from the ActionControllerBase and implements IRenderTemplate<BlockData>, letting the controller render block types. The Index method is overridden and gets the start page as rendering context. A new instance of the PreviewModel is created, and the block is programmatically added to the content area. The controller has a TemplateDescriptor "Preview" tag, ensuring that it is only used for on-page editing.

Example: The preview controller.

namespace AlloyTemplates.Controllers
    {
      [TemplateDescriptor(
        Inherited = true,
        TemplateTypeCategory = TemplateTypeCategories.MvcController, //Required as controllers for blocks are registered as MvcPartialController by default
        Tags = new[] { RenderingTags.Preview, RenderingTags.Edit },
        AvailableWithoutTag = false)]
      [VisitorGroupImpersonation]
      [RequireClientResources]
      public class PreviewController : ActionControllerBase, IRenderTemplate<BlockData>, IModifyLayout
      {
        private readonly IContentLoader _contentLoader;
    
        public PreviewController(IContentLoader contentLoader)
        {
          _contentLoader = contentLoader;
        }
    
        public IActionResult Index(IContent currentContent)
        {
          //As the layout requires a page for title etc we "borrow" the start page
          var startPage = _contentLoader.Get<StartPage>(SiteDefinition.Current.StartPage);
          var model = new PreviewModel(startPage, currentContent);
    
          return View(model);
        }
    
        public void ModifyLayout(LayoutModel layoutModel)
        {
          layoutModel.HideHeader = true;
          layoutModel.HideFooter = true;
        }
      }
    }

Preview view

Example: View for rendering the block in different widths depending on context.

@model PreviewModel
    
    <div class="row">
      <div class="span12">
        @Html.PropertyFor(m => m.PreviewContentArea)
      </div>
    </div>
    
    <div class="row">
      <div class="span8">
        @Html.PropertyFor(m => m.PreviewContentArea)
      </div>
    </div>
    
    <div class="row">
      <div class="span4">
        @Html.PropertyFor(m => m.PreviewContentArea)
      </div>
    </div>

The resulting outcome when editing and previewing a block in edit view.

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