GadgetApiController.cs

public class GadgetApiController : ApiController
{
	private readonly ITemplateResolver _templateResolver;
	private readonly IContentRenderer _contentRenderer;
	private readonly IContentRepository _contentRepository;

	public GadgetApiController(ITemplateResolver templateResolver, IContentRenderer contentRenderer, IContentRepository contentRepository)
	{
		this._templateResolver = templateResolver;
		this._contentRenderer = contentRenderer;
		this._contentRepository = contentRepository;
	}

	[System.Web.Http.HttpGet]
	public async Task<IHttpActionResult> Show(string contentReference)
	{
		//Find the content in question
		IContent matchedContent = this._contentRepository.Get<IContent>(new ContentReference(contentReference));

		if (matchedContent == null)
			throw new ContentNotFoundException("Content was not found");

		//Resolve the right Template based on Episervers own templating engine
		TemplateModel model = this._templateResolver.Resolve(HttpContext.Current, matchedContent.GetOriginalType(), TemplateTypeCategories.MvcPartial | TemplateTypeCategories.MvcPartialController, new string[0]);

		//Resolve the controller
		ControllerBase contentController = ServiceLocator.Current.GetInstance(model.TemplateType) as ControllerBase;

		//Derive the name
		string controllerName = model.Name.Replace("Controller", "");

		//Mimic the routing of our rendition 
		RouteData routeData = new RouteData();
		routeData.Values.Add("currentContent", matchedContent);
		routeData.Values.Add("controllerType", model.TemplateType);
		routeData.Values.Add("language", ContentLanguage.PreferredCulture.Name);
		routeData.Values.Add("controller", controllerName);
		routeData.Values.Add("action", "Index");
		routeData.Values.Add("node", matchedContent.ContentLink.ID);

		//Create a fake context, that can be executed based on the route
		ViewContext viewContext = new ViewContext(new ControllerContext(new HttpContextWrapper(HttpContext.Current), routeData, contentController), new FakeView(), new ViewDataDictionary(), new TempDataDictionary(), new StringWriter());

		HtmlHelper helper = new HtmlHelper(viewContext, new ViewPage());

		//Render in our fake context
		this._contentRenderer.Render(helper, new PartialRequest(), matchedContent, model);

		//Derive the output based on our template and view engine
		string html = viewContext.Writer.ToString();

		return Json(new { Html = html });
	}
  }