Render View programmatically into a string

Question

I would like to get the html code a view would generate in a string, modify it in my controller, then add it to my JsonResult.

I found code that would do what i'm talking about from a partial. I would like to do it from an aspx View though.

-- Extra explanation:

Let's say I have a page Frame.aspx that /Controller/Frame will return

I would like to get my hand on the response before it out so I can to wrap it with jsonp. I do not wish to edit the return result in code every time, this is why I want to load the view programmatically.

/Controller/Frame currently returns Frame.aspx's content: <html><body>hello</body></html>

Let's say there's a function that renders a view in a string builder

StringBuilder sb = new StringBuilder();
RenderView(sb, "Frame");

now take sb and wrap it with jsonp:

public JsonResult Frame(string callback)
{
     StringBuilder sb = new StringBuilder();
     RenderView(sb, "Frame");

     return new JsonResult
     {
         Data = "(function() { " + callback + "(" +  clientResponse + "); })();"
         ,
         JsonRequestBehavior = JsonRequestBehavior.AllowGet
     };
}

Please edit this question with more detail, and maybe some example code. There's not enough detail here to attempt an answer. — Brandon Satrom
– Brandon Satrom, Commented Jul 13, 2010 at 3:55
Please don't include tags like "C#" in the title. It's just redundant. Leaving them in the tags is enough. — John Saunders
– John Saunders, Commented Jul 13, 2010 at 4:33
@Graphain thanks for the link. This is kind of what i'm looking for except that it doesn't work with mvc2. I modified it but now I'm running into another problem: when i'm returning a JsonResult, my code is attempting to modify the http headers that have already been set and is throwing an exception. I'll webclient the page for now until i find a better solution... — Abdo
– Abdo, Commented Jul 13, 2010 at 4:49
RenderView must be sending it to the client as well as the string builder then. stackoverflow.com/questions/2746333/… looks relevant. — Matt Mitchell
– Matt Mitchell, Commented Jul 13, 2010 at 4:51

John Landheer · Accepted Answer · 2010-08-13 17:30:46Z

This works like a charm (got it through SO).

I use it like this:

public class OfferController : Controller
{
    [HttpPost]
    public JsonResult EditForm(int Id)
    {
        var model = Mapper.Map<Offer, OfferEditModel>(_repo.GetOffer(Id));

        return Json(new { status = "ok", partial = this.RenderPartialViewToString("Edit", model) });
    }
}



public static partial class ControllerExtensions
{
    public static string RenderPartialViewToString(this ControllerBase controller, string partialPath, object model)
    {
        if (string.IsNullOrEmpty(partialPath))
            partialPath = controller.ControllerContext.RouteData.GetRequiredString("action");

        controller.ViewData.Model = model;

        using (StringWriter sw = new StringWriter())
        {
            ViewEngineResult viewResult = ViewEngines.Engines.FindPartialView(controller.ControllerContext, partialPath);
            ViewContext viewContext = new ViewContext(controller.ControllerContext, viewResult.View, controller.ViewData, controller.TempData, sw);
            // copy model state items to the html helper 
            foreach (var item in viewContext.Controller.ViewData.ModelState)
                if (!viewContext.ViewData.ModelState.Keys.Contains(item.Key))
                {
                    viewContext.ViewData.ModelState.Add(item);
                }


            viewResult.View.Render(viewContext, sw);

            return sw.GetStringBuilder().ToString();
        }
    }
}

a7drew · Accepted Answer · 2010-07-14 15:18:05Z

Mike Hadlow blogged about a function called CaptureActionHtml() that does this. I've used it to compose large reports out of smaller, more manageable reports and then pass them around.

http://mikehadlow.blogspot.com/2008/06/mvc-framework-capturing-output-of-view_05.html

using System;
using System.IO;
using System.Web;
using System.Web.Mvc;

namespace Suteki.Common.Extensions
{
    public static class ControllerExtensions
    {
        /// <summary>
        /// Captures the HTML output by a controller action that returns a ViewResult
        /// </summary>
        /// <typeparam name="TController">The type of controller to execute the action on</typeparam>
        /// <param name="controller">The controller</param>
        /// <param name="action">The action to execute</param>
        /// <returns>The HTML output from the view</returns>
        public static string CaptureActionHtml<TController>(
            this TController controller,
            Func<TController, ViewResult> action)
            where TController : Controller
        {
            return controller.CaptureActionHtml(controller, null, action);
        }

        /// <summary>
        /// Captures the HTML output by a controller action that returns a ViewResult
        /// </summary>
        /// <typeparam name="TController">The type of controller to execute the action on</typeparam>
        /// <param name="controller">The controller</param>
        /// <param name="masterPageName">The master page to use for the view</param>
        /// <param name="action">The action to execute</param>
        /// <returns>The HTML output from the view</returns>
        public static string CaptureActionHtml<TController>(
            this TController controller,
            string masterPageName,
            Func<TController, ViewResult> action)
            where TController : Controller
        {
            return controller.CaptureActionHtml(controller, masterPageName, action);
        }

        /// <summary>
        /// Captures the HTML output by a controller action that returns a ViewResult
        /// </summary>
        /// <typeparam name="TController">The type of controller to execute the action on</typeparam>
        /// <param name="controller">The current controller</param>
        /// <param name="targetController">The controller which has the action to execute</param>
        /// <param name="action">The action to execute</param>
        /// <returns>The HTML output from the view</returns>
        public static string CaptureActionHtml<TController>(
            this Controller controller,
            TController targetController, 
            Func<TController, ViewResult> action)
            where TController : Controller
        {
            return controller.CaptureActionHtml(targetController, null, action);
        }

        /// <summary>
        /// Captures the HTML output by a controller action that returns a ViewResult
        /// </summary>
        /// <typeparam name="TController">The type of controller to execute the action on</typeparam>
        /// <param name="controller">The current controller</param>
        /// <param name="targetController">The controller which has the action to execute</param>
        /// <param name="masterPageName">The name of the master page for the view</param>
        /// <param name="action">The action to execute</param>
        /// <returns>The HTML output from the view</returns>
        public static string CaptureActionHtml<TController>(
            this Controller controller,
            TController targetController, 
            string masterPageName,
            Func<TController, ViewResult> action)
            where TController : Controller
        {
            if (controller == null)
            {
                throw new ArgumentNullException("controller");
            }
            if (targetController == null)
            {
                throw new ArgumentNullException("targetController");
            }
            if (action == null)
            {
                throw new ArgumentNullException("action");
            }

            // pass the current controller context to orderController
            var controllerContext = controller.ControllerContext;
            targetController.ControllerContext = controllerContext;

            // replace the current context with a new context that writes to a string writer
            var existingContext = System.Web.HttpContext.Current;
            var writer = new StringWriter();
            var response = new HttpResponse(writer);
            var context = new HttpContext(existingContext.Request, response) {User = existingContext.User};
            System.Web.HttpContext.Current = context;

            // execute the action
            var viewResult = action(targetController);

            // change the master page name
            if (masterPageName != null)
            {
                viewResult.MasterName = masterPageName;
            }

            // we have to set the controller route value to the name of the controller we want to execute
            // because the ViewLocator class uses this to find the correct view
            var oldController = controllerContext.RouteData.Values["controller"];
            controllerContext.RouteData.Values["controller"] = typeof(TController).Name.Replace("Controller", "");

            // execute the result
            viewResult.ExecuteResult(controllerContext);

            // restore the old route data
            controllerContext.RouteData.Values["controller"] = oldController;

            // restore the old context
            System.Web.HttpContext.Current = existingContext;

            return writer.ToString();
        }
    }
}

This works fine for me with V3.5 and MVc1.0. but when I upgraded it to V4.0 and MVC 2.0 the context returns null.. any idea??

Gokul · Accepted Answer · 2011-04-05 18:26:41Z

Here is another workaround for capturing the view in MVC 2.0 and >net 4.0. I just added few lines of code to Andrews original content.

 public static class ControllerExtensions
    {

        /// <summary>
        /// Captures the HTML output by a controller action that returns a ViewResult
        /// </summary>
        /// <typeparam name="TController">The type of controller to execute the action on</typeparam>
        /// <param name="controller">The controller</param>
        /// <param name="action">The action to execute</param>
        /// <returns>The HTML output from the view</returns>
        public static string CaptureActionHtml<TController>(
            this TController controller,
            Func<TController, ViewResult> action)
            where TController : Controller
        {
            return controller.CaptureActionHtml(controller, null, action);
        }

        /// <summary>
        /// Captures the HTML output by a controller action that returns a ViewResult
        /// </summary>
        /// <typeparam name="TController">The type of controller to execute the action on</typeparam>
        /// <param name="controller">The controller</param>
        /// <param name="masterPageName">The master page to use for the view</param>
        /// <param name="action">The action to execute</param>
        /// <returns>The HTML output from the view</returns>
        public static string CaptureActionHtml<TController>(
            this TController controller,
            string masterPageName,
            Func<TController, ViewResult> action)
            where TController : Controller
        {
            return controller.CaptureActionHtml(controller, masterPageName, action);
        }

        /// <summary>
        /// Captures the HTML output by a controller action that returns a ViewResult
        /// </summary>
        /// <typeparam name="TController">The type of controller to execute the action on</typeparam>
        /// <param name="controller">The current controller</param>
        /// <param name="targetController">The controller which has the action to execute</param>
        /// <param name="action">The action to execute</param>
        /// <returns>The HTML output from the view</returns>
        public static string CaptureActionHtml<TController>(
            this Controller controller,
            TController targetController,
            Func<TController, ViewResult> action)
            where TController : Controller
        {
            return controller.CaptureActionHtml(targetController, null, action);
        }




        /// <summary>
        /// Captures the HTML output by a controller action that returns a ViewResult
        /// </summary>
        /// <typeparam name="TController">The type of controller to execute the action on</typeparam>
        /// <param name="controller">The current controller</param>
        /// <param name="targetController">The controller which has the action to execute</param>
        /// <param name="masterPageName">The name of the master page for the view</param>
        /// <param name="action">The action to execute</param>
        /// <returns>The HTML output from the view</returns>
        ///     
  public static string CaptureActionHtml<TController>(this Controller controller, TController targetController, string masterPageName, Func<TController, ViewResult>  action) where TController : Controller

       {
    if (controller == null)
    {
    throw new ArgumentNullException("controller");
    }
    if (targetController == null)
    {
    throw new ArgumentNullException("targetController");
    }
    if (action == null)
    {
    throw new ArgumentNullException("action");
    }
    // pass the current controller context to orderController
    var controllerContext = controller.ControllerContext;
    targetController.ControllerContext = controllerContext;

    // replace the current context with a new context that writes to a string writer
    var existingContext = HttpContext.Current;
    var writer = new StringWriter();
    var response = new HttpResponse(writer);
    var context = new HttpContext(existingContext.Request, response) { User = existingContext.User };
    HttpContext.Current = context;

    // execute the action
    var viewResult = action(targetController);

    // change the master page name
    if (masterPageName != null)
    {
    viewResult.MasterName = masterPageName;
    }

    // we have to set the controller route value to the name of the controller we want to execute
    // because the ViewLocator class uses this to find the correct view
    var oldController = controllerContext.RouteData.Values["controller"];
    controllerContext.RouteData.Values["controller"] = typeof(TController).Name.Replace("Controller", "");

    // execute the result
    viewResult.ExecuteResult(controllerContext);

    StringWriter sw = new StringWriter();
    var xx = targetController.TempData["pdf"];
    //var viewContext = new ViewContext(controllerContext, viewResult.View, new ViewDataDictionary(targetController.ViewData.Model), new TempDataDictionary(), sw);
    var viewContext = new ViewContext(controllerContext, viewResult.View, viewResult.ViewData, new TempDataDictionary(), sw);
    viewResult.View.Render(viewContext, HttpContext.Current.Response.Output);
    response.Flush();

    // restore the old route data
    controllerContext.RouteData.Values["controller"] = oldController;

    // restore the old context
    HttpContext.Current = existingContext;

    return sw.ToString();
    } 



    }
}

cheers!!

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