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Preview rendering for blocks

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 the block's appearance when added to content areas with different widths.

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 blocks in the On-Page Editing view, you can create a preview page 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.

Create a block preview template

The following example creates these components to build a preview that you can use for 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.



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 {

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. An 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 {
    Inherited = true,
    TemplateTypeCategory = TemplateTypeCategories.MvcController, //Required as controllers for blocks are registered as MvcPartialController by default
    Tags = new [] {
      RenderingTags.Preview, RenderingTags.Edit
    AvailableWithoutTag = false)]
  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 class="row">
  <div class="span8">
    @Html.PropertyFor(m => m.PreviewContentArea)
<div class="row">
  <div class="span4">
    @Html.PropertyFor(m => m.PreviewContentArea)

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