Render a view as a string

Question

Hi all!

I'm wanting to output two different views (one as a string that will be sent as an email), and the other the page displayed to a user.

Is this possible in ASP.NET MVC beta?

I've tried multiple examples:

RenderPartial to String in ASP.NET MVC Beta
If I use this example, I receive the "Cannot redirect after HTTP headers have been sent.".

MVC Framework: Capturing the output of a view
If I use this, I seem to be unable to do a redirectToAction, as it tries to render a view that may not exist. If I do return the view, it is completely messed up and doesn't look right at all.

Does anyone have any ideas/solutions to these issues i have, or have any suggestions for better ones?

Many thanks!

Below is an example. What I'm trying to do is create the GetViewForEmail method:

public ActionResult OrderResult(string ref)
{
  //Get the order
  Order order = OrderService.GetOrder(ref);

  //The email helper would do the meat and veg by getting the view as a string
  //Pass the control name (OrderResultEmail) and the model (order)
  string emailView = GetViewForEmail("OrderResultEmail", order);

  //Email the order out
  EmailHelper(order, emailView);
  return View("OrderResult", order);
}

Accepted answer from Tim Scott (changed and formatted a little by me):

public virtual string RenderViewToString(
  ControllerContext controllerContext,
  string viewPath,
  string masterPath,
  ViewDataDictionary viewData,
  TempDataDictionary tempData)
{
  Stream filter = null;
  ViewPage viewPage = new ViewPage();

  //Right, create our view
  viewPage.ViewContext = new ViewContext(controllerContext, new WebFormView(viewPath, masterPath), viewData, tempData);

  //Get the response context, flush it and get the response filter.
  var response = viewPage.ViewContext.HttpContext.Response;
  response.Flush();
  var oldFilter = response.Filter;

  try
  {
      //Put a new filter into the response
      filter = new MemoryStream();
      response.Filter = filter;

      //Now render the view into the memorystream and flush the response
      viewPage.ViewContext.View.Render(viewPage.ViewContext, viewPage.ViewContext.HttpContext.Response.Output);
      response.Flush();

      //Now read the rendered view.
      filter.Position = 0;
      var reader = new StreamReader(filter, response.ContentEncoding);
      return reader.ReadToEnd();
  }
  finally
  {
      //Clean up.
      if (filter != null)
      {
        filter.Dispose();
      }

      //Now replace the response filter
      response.Filter = oldFilter;
  }
}

Example usage

Assuming a call from the controller to get the order confirmation email, passing the Site.Master location.

string myString = RenderViewToString(this.ControllerContext, "~/Views/Order/OrderResultEmail.aspx", "~/Views/Shared/Site.Master", this.ViewData, this.TempData);

Answer 1

Do i understand correct if you want to do something like this: When the user does something he should get an email and a text on the screen?

Then why don't the model send the email? Why would you need the email to be sent to a view?

Answer 2

I would create a new View class deriving from the original view and overriding the ouput method.

Answer 3

This works for me:

public virtual string RenderView(ViewContext viewContext)
{
    var response = viewContext.HttpContext.Response;
    response.Flush();
    var oldFilter = response.Filter;
    Stream filter = null;
    try
    {
        filter = new MemoryStream();
        response.Filter = filter;
        viewContext.View.Render(viewContext, viewContext.HttpContext.Response.Output);
        response.Flush();
        filter.Position = 0;
        var reader = new StreamReader(filter, response.ContentEncoding);
        return reader.ReadToEnd();
    }
    finally
    {
        if (filter != null)
        {
            filter.Dispose();
        }
        response.Filter = oldFilter;
    }
}

Answer 4

Thanks for the blog, got me a bit further, though I'm not sure if I missed something or if the rc 2 of ASP.NET MVC just handle things differently. I couldn't get your sample to work and I was stuck last night at 5 in the morning with a lot of email handling code that depended on this to work. I got the 'can't redirect after headers have been sent' error over and over again no matter what i tried. I didn't feel like rewriting too much code, so I thought a hack might be better than nothing.

Here's my code if anyone can make use of it. It's not very pretty, but at least it works until the MVC team realeases a new version with an EmailResult or whatever they come up with.

If you experience encoding problems with the output, try saving your view .aspx files as 'Unicode UTF-8 with signature'. Worked for me.

I still can't figure out how to avoid using the Current HttpContext, I've looked into Phil Haacked's unit testing code and 3-4 other promising ideas but with no luck. I get an empty string as the output if I don't reference the Current context.

Jacob Frost, Copenhagen

    public static void SendView(IEnumerable<User> recipients, string viewName, string masterName, object viewData)
    {
        string viewPath = viewName.IndexOfAny(new char[] { '~', '/' }) > -1 ? viewName : string.Format("~/Views/Mail/{0}.aspx", viewName);
        string masterPath = null;
        if (masterName != null)
        {
            masterPath = masterName.IndexOfAny(new char[] { '~', '/' }) > -1 ? masterName : string.Format("~/Views/Mail/{0}.Master", masterName);
        }

            var httpStream = new MemoryStream();
            var httpWriter = new StreamWriter(httpStream, Encoding.Unicode);

            var viewPage = new ViewPage();

            var response = HttpContext.Current.Response;
            response.ContentEncoding = Encoding.Unicode;

            viewPage.ViewContext = new ViewContext(
                new ControllerContext
                {
                    HttpContext = new HttpContextWrapper(
                        new HttpContext(HttpContext.Current.Request, response)
                    )
                },
                new WebFormView(viewPath, masterPath /* ignored if null */),
                new ViewDataDictionary(viewData /* ignored if null */),
                new TempDataDictionary()
            );


            // HACK: Inject custom TextWriter into the http response, then render, then put the response in it's original state and return
            var httpWriterField = response.GetType().GetField("_httpWriter", BindingFlags.NonPublic | BindingFlags.Instance);
            var privateHttpWriter = httpWriterField.GetValue(response);
            httpWriterField.SetValue(response, null);

            var writerField = response.GetType().GetField("_writer", BindingFlags.NonPublic | BindingFlags.Instance);
            writerField.SetValue(response, httpWriter);

            viewPage.ViewContext.View.Render(viewPage.ViewContext, null /* ignored by asp.net framework &@#*!@!# */);

            httpWriterField.SetValue(response, privateHttpWriter);
            writerField.SetValue(response, privateHttpWriter);


            string output = Encoding.Unicode.GetString(httpStream.ToArray());

            // Now you have the view output as a string, and headers have not been sent, so you can return a RedirectToAction in your calling code if you wish.


           // Send email as normally. Beware that you might get problems with sending asynchroneous as your controller or view needs an Async attribute for this. I wrote a custom threading solution, as I thought the attribute solution was too much to ask of the calling code.

Answer 5

I met the same problem with creating report. After trying all above solution, I met some exception related to the HTTP header. It does not allow me to redirect to action or return any ActionResult later.

However, I found another way to solve. Please go to this article on my blog: http://trandangkhoa.blogspot.com/2009/05/asp-net-mvc-print-excel-file-using-aspx.html

The idea is very simple: using HttpClient to get HTML content from the view:

Answer 6

Quick tip

For a strongly typed Model just add it to the ViewData.Model property before passing to RenderViewToString. e.g

this.ViewData.Model = new OrderResultEmailViewModel(order);
string myString = RenderViewToString(this.ControllerContext, "~/Views/Order/OrderResultEmail.aspx", "~/Views/Shared/Site.Master", this.ViewData, this.TempData);

Answer 7

I am using MVC 1.0 RTM and none of the above solutions worked for me. But this one did:

Public Function RenderView(ByVal viewContext As ViewContext) As String

    Dim html As String = ""

    Dim response As HttpResponse = HttpContext.Current.Response

    Using tempWriter As New System.IO.StringWriter()

        Dim privateMethod As MethodInfo = response.GetType().GetMethod("SwitchWriter", BindingFlags.NonPublic Or BindingFlags.Instance)

        Dim currentWriter As Object = privateMethod.Invoke(response, BindingFlags.NonPublic Or BindingFlags.Instance Or BindingFlags.InvokeMethod, Nothing, New Object() {tempWriter}, Nothing)

        Try
            viewContext.View.Render(viewContext, Nothing)
            html = tempWriter.ToString()
        Finally
            privateMethod.Invoke(response, BindingFlags.NonPublic Or BindingFlags.Instance Or BindingFlags.InvokeMethod, Nothing, New Object() {currentWriter}, Nothing)
        End Try

    End Using

    Return html

End Function

Answer 8

I found a new solution that renders a view to string without having to mess with the Response stream of the current HttpContext (which doesn't allow you to change the response's ContentType or other headers).

Basically, all you do is create a fake HttpContext for the view to render itself:

/// <summary>Renders a view to string.</summary>
public static string RenderViewToString(this Controller controller,
                                        string viewName, object viewData) {
    //Create memory writer
    var sb = new StringBuilder();
    var memWriter = new StringWriter(sb);

    //Create fake http context to render the view
    var fakeResponse = new HttpResponse(memWriter);
    var fakeContext = new HttpContext(HttpContext.Current.Request, fakeResponse);
    var fakeControllerContext = new ControllerContext(
        new HttpContextWrapper(fakeContext),
        controller.ControllerContext.RouteData,
        controller.ControllerContext.Controller);

    var oldContext = HttpContext.Current;
    HttpContext.Current = fakeContext;

    //Use HtmlHelper to render partial view to fake context
    var html = new HtmlHelper(new ViewContext(fakeControllerContext,
        new FakeView(), new ViewDataDictionary(), new TempDataDictionary()),
        new ViewPage());
    html.RenderPartial(viewName, viewData);

    //Restore context
    HttpContext.Current = oldContext;    

    //Flush memory and return output
    memWriter.Flush();
    return sb.ToString();
}

/// <summary>Fake IView implementation used to instantiate an HtmlHelper.</summary>
public class FakeView : IView {
    #region IView Members

    public void Render(ViewContext viewContext, System.IO.TextWriter writer) {
        throw new NotImplementedException();
    }

    #endregion
}

This works on ASP.NET MVC 1.0, together with ContentResult, JsonResult, etc. (changing Headers on the original HttpResponse doesn't throw the "Server cannot set content type after HTTP headers have been sent" exception).

Update: in ASP.NET MVC 2.0 RC, the code changes a bit because we have to pass in the StringWriter used to write the view into the ViewContext:

//...

//Use HtmlHelper to render partial view to fake context
var html = new HtmlHelper(
    new ViewContext(fakeControllerContext, new FakeView(),
        new ViewDataDictionary(), new TempDataDictionary(), memWriter),
    new ViewPage());
html.RenderPartial(viewName, viewData);

//...

Update 2: I have an expanded blog post about the solution and its differences with the other methods. Here's a second blog post about performance of the different solutions.

Answer 9

This solution worked nicely for me

http://msug.vn.ua/blogs/bobasoft/archive/2010/01/07/render-partialview-to-string-asp-net-mvc.aspx

Answer 10

To repeat from a more unknown question, take a look at MvcIntegrationTestFramework.

It makes saves you writing your own helpers to stream result and is proven to work well enough. I'd assume this would be in a test project and as a bonus you would have the other testing capabilities once you've got this setup. Main bother would probably be sorting out the dependency chain.

 private static readonly string mvcAppPath = 
     Path.GetFullPath(AppDomain.CurrentDomain.BaseDirectory 
     + "\\..\\..\\..\\MyMvcApplication");
 private readonly AppHost appHost = new AppHost(mvcAppPath);

    [Test]
    public void Root_Url_Renders_Index_View()
    {
        appHost.SimulateBrowsingSession(browsingSession => {
            RequestResult result = browsingSession.ProcessRequest("");
            Assert.IsTrue(result.ResponseText.Contains("<!DOCTYPE html"));
        });
}

Answer 11

Here's what I came up with, and it's working for me (MVC2)

    protected string RenderViewToString<T>(string viewPath, T model) {
        using (var writer = new StringWriter()) {
            var view = new WebFormView(viewPath);
            var vdd = new ViewDataDictionary<T>(model);
            var viewCxt = new ViewContext(ControllerContext, view, vdd, new TempDataDictionary(), writer);
            viewCxt.View.Render(viewCxt, writer);
            return writer.ToString();
        }
    }

Answer 12

Here is another solution to this problem. It is based on the MVC source, works with Html/Ajax/Url helpers, and is context-aware so it doesn't require the full path to the partial view file: http://craftycodeblog.com/2010/05/15/asp-net-mvc-render-partial-view-to-string/

Answer 13

After a little looking around I came across this blog post

http://craftycodeblog.com/2010/05/15/asp-net-mvc-render-partial-view-to-string

In here the author provides a solution by creating a subclass to the Controller.

This isn’t a bad solution except it pollutes your inheritance hierarchy. So I rewrote it as a C# extension method.

This allows you to use the rendering functions without polluting your object hierarchy.

View the code: http://learningdds.com/public/ControllerExtension.cs