ASP.NET MVC and Razor Engine used to render ASP.NET MVC views are combined to create a great rendering engine for text and HTML templates. Together they make it easy to combine text, template data, and code to produce rich HTML output. Razor rendering in ASP.NET MVC is typically reserved solely for rendering views and generating HTML output as part of an MVC request. But as I describe in this article, it's also possible to render MVC Razor views directly in a chain to capture the output and render those views outside of the direct context of an MVC web request.
I find it common for the web apps I develop to require text merging capabilities that are outside the scope of ASP.NET MVC requirements. For example, I often need to create merge text strings for email order confirmations, new account and password recovery notifications, or capture some merge results and store them on disk or in a database. All of this requires the capture of textual content, which is often best handled through templates rather than static text embedded in the application's source code. Razor Views is ideal for this.
I also often need to render text output in ASP.NET application code that is out of the context of an ASP.NET MVC request. For example ASP.NETapplication errorThe event is outside of an ASP.NET MVC request loop, but can benefit greatly from a Razor View template to render the error page output. Likewise, ASP.NET Web API requests that for one reason or another need to display HTML output can also benefit greatly from Razor View rendering to generate HTML output. In summary, there are some places in typical ASP.NET applications that fall outside the scope of an ASP.NET MVC request and can still benefit greatly from the ASP.NET MVC Razor View Engine.
In this article, I show how you can render ASP.NET MVC Razor Views in unconventional ways, e.g. For example, by capturing the Razor View output in a string for use in mail merge or saving, and for outputting Razor Views outside of the context of an ASP. NET MVC request, either for rendering the output or for text capture purposes.
I will focus on using Razor Views in ASP.NET applications as this is a common scenario that allows you to take advantage of all the benefits found when implementing ASP.NET MVC Razor. In a future article, I'll explain how the Razor engine is hosted explicitly outside of ASP.NET, which is a bit more complex and doesn't allow access to the ASP.NET MVC Razor implementation.
It's not very well known, but with a little trick you can make ASP.NET MVC Razor Views render outside of MVC.
Understanding Razor in ASP.NET MVC
The Razor Engine is not directly part of ASP.NET MVC. Instead, Razor is a fully self-contained and self-contained HTML template rendering engine that runs entirely outside of MVC and ASP.NET frameworks. For example, Razor itself can be hosted in a desktop app, console app, or service. Microsoft offers two different custom implementations of the Razor Engine at:
- ASP.NET-MVC
- ASP.NET Web Pages
In addition, you can create your own plugin implementation of Razor to host in your own apps. The two implementations provided have slightly different behavior; are optimized for their respective environments. Razor allows you to create a custom Razor engine that can be used in any .NET environment. In this article, I'll focus specifically on the implementation of ASP.NET MVC Razor.
The ASP.NET MVC Razor implementation is closely related to ASP.NET and MVC, and the view model (WebViewPage class) contains some MVC-specific functionality as well as legacy references to the controller. In other words, MVC Razor was built with MVC in mind.
Unsurprisingly, it's easier to render MVC Razor views from within MVC apps. First, let's see how you can capture a view's output to a string in an MVC controller application.
Render an MVC Razor view to a string
When running in an MVC request, it's very easy to render an MVC view and capture its output. Essentially, you can simulate the process that MVC performs when rendering a view without theVista()method of onemethod🇧🇷 the codeListing 1shows a static helper method that can be used to generically render a display by route name in a string.
Listing 1: Rendering a Razor view to a controller string
static string RenderViewToString(ControllerContext context, string viewPath, object model = null, partial boolean = false) { // first find the ViewEngine for this view ViewEngineResult viewEngineResult = null; if (partial) viewEngineResult = ViewEngines.Engines.FindPartialView(context, viewPath); else viewEngineResult = ViewEngines.Engines.FindView(context, viewPath, null); if (viewEngineResult == null) throws a new FileNotFoundException("Cannot find view"); // get the view and attach the model to display the data var view = viewEngineResult.View; context.Controller.ViewData.Model = model; string result = null; using (var sw = new StringWriter()) { var ctx = new ViewContext (context, view, context.Controller.ViewData, context.Controller.TempData, sw); ver.Render(ctx, sw); Result = sw.ToString(); } returns result;}To call this method from a controller method, you can use code like the following:
Public ActionResult RenderViewToString(){ var model = new EmailConfirmationModel() { FirstName = "John", LastName = "Doe", InvoiceNo = "DoeBoy1" }; string html = RenderViewToString(ControllerContext, "~/views/samples/ConfirmationEmail.cshtml", model, true); // do something with the text e.g. B. send an email with the text // For the demo, just slide into a view and display ViewBag.RenderedHtml = html; returnview();}LosRenderViewToString()The method works by providing a controller context and a virtual view path (ie.~/views/item/page.cshtml) and optional model data passed to the view. You can also pass a flag to render a partial view, which is common for standalone template pages that are not supposed to render a _Layout page.
The routine works with theFindView()method notsee engineto get the ASP.NET Virtual Path Provider view. You pass a virtual route (i.e.~/rutavirtuell) to refer to the model to render.
After the view is created, the model is assigned to the passed ControllerContext, or if the controller already has a model assignedViewData.Modelproperty uses this template. Context is critical to many aspects of Razor view rendering, including model mapping and as the basis for creating the ViewContext. Context is the key that binds the Razor View and ASP.NET controller, model, and context together.
This is an important point for using ASP.NET MVC Razor Views. One way or another, a ControllerContext must be available. The context is needed to allocate the model and create the ViewContext instance that can render the view in aLyricsExample. In the code snippet above, I have a ControllerContext available because the request is being executed in the context of an MVC Controller action method.
This code is simple and easy to understand, and works very well within the confines of an MVC application in controller actions. If you need to send email confirmations or perform logging or data tasks as part of an MVC page request, this simple mechanism is all you need.
Unfortunately, ASP.NET MVC's implementation of Razor is closely related to ASP.NET, making Razor MVC difficult to use outside of ASP.NET.
Get a ControllerContext outside of MVC
What happens if no ControllerContext is available, e.g. B. in static code or in an HttpHandler or HttpModule or even in a web API call?
as you can see in itRenderViewToString()InsideListing 1, a ControllerContext is required to render a view. There really is no getting around this as the context provides the basic information for several key components exposed in the view such as: So it looks like the view is tightly coupled to the controller...
But surprisingly, the driver clutch is relatively loose; It is possible to create a ControllerContext generically from each controller instance and pass it to a completely independent view. You can use this generated context and pass it toRenderViewToString()🇧🇷 With this trick it's possible to render a view outside of the MVC framework as long as an HttpContext instance is available.
The method inlisting 2demonstrates how to create an arbitrary Controller instance with an attached ControllerContext, which can then be used to invoke itrenderview().
Listing 2: Creating a generic controller instance and context
public static T CreateController<T>(RouteData routeData = null) where T : Controller, new(){ // create a separate controller instance T controller = new T(); // Get the context container of HttpContext if the HttpContextBase container is available; if (System.Web.HttpContext.Current != null) wrapper = new HttpContextWrapper(System.Web.HttpContext.Current); else throw new InvalidOperationException("Cannot create controller context when no active HttpContext instance is available"); if (routeData == null) routeData = new RouteData(); // Add controller routing if not present if (!routeData.Values.ContainsKey("controller") && !routeData.Values.ContainsKey("Controller")) routeData.Values.Add("controller", controller.GetType ( ) .Name.ToLower().Replace("Controller", "")); controller.ControllerContext = new ControllerContext(wrapper, route data, controller); return handler;}You can now call this method to generically create a controller anywhere in an ASP.NET application as long as an HttpContext is available.listing 3shows an example of using an MVC view to render error information from an HttpModule that is outside of the MVC runtime.
Listing 3: Rendering MVC from an Http module outside of MVC
Public class ErrorModule: ApplicationErrorModule{ protected override void OnDisplayError(WebErrorHandler errorHandler, model ErrorViewModel) { var response = HttpContext.Current.Response; // Create any controller instance var controller = ViewRenderer.CreateController<GenericController>(); string html = ViewRenderer.RenderPartialView("~/views/shared/Error.cshtml", model, controller.ControllerContext); HttpContext.Current.Server.ClearError(); Response.TrySkipIisCustomErrors = true; Response.ClearContent(); Response.StatusCode = 500; answer.Write(html); }}// *any* controller class works for templatepublic class GenericController : Controller{ }The code in this example runs in an HttpModule outside of the MVC scope, but is still able to render an MVC view. It is an error handling module that catches all unhandled ASP.NET errors (thinkapplication error) and forwards it to theOnDisplayError()Method of handling display error info I use the forRenderViewToString()to render the error response page.
The rendering code uses theCreateControlador()method to instantiate a controller, passing in its ControllerContextRenderViewToString()🇧🇷 Note that every instance of the controller works as you can see from the gapgeneric controllerClass I created as part of the sampler. In my own MVC helper libraries, theRendererClass creates simple knowledgeEmpty controllerentity that lives in theAssistantassemble and use if notControllerContextThe instance is passed explicitly.
As long as you're inside ASP.NET, even things likeinquiryObject or UrlHelpers work because they can be accessed by the controller context outside ofHttpContextoused in conjunction with the controller context when created.
A ViewRenderer class
The ViewRenderer class used inlisting 2jlisting 3is an extension of the methods shown above. The class offersRenderViewToString()jRenderPartialViewToString()methods thatCreateControlador()method shown inlisting 2and static and instance methods to easily handle display rendering. The source code for the ViewRenderer class can be found in the example accompanying this article or in the West Wind Toolkit GitHub repository (http://tinyurl.com/lpz877z🇧🇷 You can also find the ViewRenderer class as part of Westwind.Web.Mvc NuGet (http://tinyurl.com/morbw6e).
It's possible to use Razor outside of ASP.NET, but it's not the same MVC Razor implementation and it takes a lot more work to set it up.
(Video) ASP.NET Core - Partials View in Razor MVC Rendern
Another use case: Web API
Another use case for Razor rendered HTML is the ASP.NET Web API. Although the APIs return data, when building hypermedia systems or mixed mode APIs, it is not uncommon for the APIs to also generate HTML output for some requests. Since the web API can run on and has access to ASP.NETHttpContext.Real, you can use the ViewRenderer from an API controller method or even from a custom MediaFormatter.
to prove itlisting 4shows a simple API controller method that looks up HTML clients and returns an HTML response or raw data when JSON or XML is requested.
Listing 4 A Web API Controller that renders a Razor View
public class CustomerController: ApiController{ [HttpGet] public HttpResponseMessage Customer(int id = 0) { var customer = new Customer() { Id = id, Name = "Jimmy Roe", Address = "123 Nowhere Lane\r\nJede Stadt, EUA ", E-Mail ="jroe@doeboy.com" }; string accept = Request.Headers.GetValues("Accept").FirstOrDefault(); if (!string.IsNullOrEmpty(accept) && accept.ToLower().Contains("text/html")) { var html = ViewRenderer.RenderView("~/views/samples/customerapi.cshtml", cliente); var message=new HttpResponseMessage(HttpStatusCode.OK); message.Content = new StringContent(html, Encoding.UTF8, "text/html"); Rückgabenachricht;} return Request.CreateResponse<Client>(HttpStatusCode.OK, cliente);}}The example is of course simple: any switching logic must be delegated to a custom media type formatter or other kernel that can automatically determine which view to render. Other requests may also always return an HTML response, such as those returning mixed text data such as acknowledgments or other dynamic documents. In this scenario, there are some interesting ways to allow building complete systems that include data and text or HTML content via a single API implementation.
Cut and dice with a knife
Razor is a powerful template implementation that is very useful for generating text and HTML output for all sorts of purposes. As you saw in this article, you can easily use ASP.NET MVC Razor Views from almost anywhere in your ASP.NET applications with the helper class provided here.
Whether it's generating text for confirmation emails, generating output for non-MVC requirements like custom controllers or modules, or occasionally needing an HTML response in a web API application , as long as the ASP.NET runtime andHttpContext.Realis available, you can use MVC Razor views in your ASP.NET web applications using the techniques described in this article.
For me, this was an important feature that I use in almost every web application I develop these days because it helps me avoid hard-coded text in applications. Razor makes it easy to manage document templates with the tools I already use in my app, and that's the way it should be.