Rectangle 27 29

This is a solution that is working with ASP.Net MVC 1.0 (many that claim to work with beta 3 don't work with 1.0), doesn't suffer of the 'Server cannot set content type after HTTP headers have been sent' problem and can be called from within a controller (not only a view):

/// <summary>
/// Render a view into a string. It's a hack, it may fail badly.
/// </summary>
/// <param name="name">Name of the view, that is, its path.</param>
/// <param name="data">Data to pass to the view, a model or something like that.</param>
/// <returns>A string with the (HTML of) view.</returns>
public static string RenderPartialToString(string controlName, object viewData) {
    ViewPage viewPage = new ViewPage() { ViewContext = new ViewContext() };
    viewPage.Url = GetBogusUrlHelper();

    viewPage.ViewData = new ViewDataDictionary(viewData);
    viewPage.Controls.Add(viewPage.LoadControl(controlName));

    StringBuilder sb = new StringBuilder();
    using (StringWriter sw = new StringWriter(sb)) {
        using (HtmlTextWriter tw = new HtmlTextWriter(sw)) {
            viewPage.RenderControl(tw);
        }
    }

    return sb.ToString();
}

public static UrlHelper GetBogusUrlHelper() {
  var httpContext = HttpContext.Current;

  if (httpContext == null) {
    var request = new HttpRequest("/", Config.Url.ToString(), "");
    var response = new HttpResponse(new StringWriter());
    httpContext = new HttpContext(request, response);
  }

  var httpContextBase = new HttpContextWrapper(httpContext);
  var routeData = new RouteData();
  var requestContext = new RequestContext(httpContextBase, routeData);

  return new UrlHelper(requestContext);
}

It's a static method you can drop somewhere you find it convenient. You can call it this way:

string view = RenderPartialToString("~/Views/Controller/AView.ascx", someModelObject);

This is still something which is frequently needed on any major MVC project. So thanks for the method

This doesn't seem to work for me because my partials make use of the UrlHelper class stuffed into the Url property of the ViewUserControl, and this method seems to leave that property null, resulting in Exceptions on my helper calls. Any advice?

Michael, maybe some info in stackoverflow.com/questions/2031995/ can help you. I don't remember having trouble with Url though and I think I was using it.

asp.net mvc - Getting a Partial View's HTML from inside of the control...

asp.net-mvc viewusercontrol render-html
Rectangle 27 27

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);

//...

There is no RenderPartial method on the HtmlHelper object. This is not possible - html.RenderPartial(viewName, viewData);

In ASP.NET MVC release 1.0 there are a couple of RenderPartial extension methods. The one I'm using in particular is System.Web.Mvc.Html.RenderPartialExtensions.RenderPartial(this HtmlHelper, string, object). I'm unaware whether the method has been added in the latest revisions of MVC and wasn't present in earlier ones.

Thanks. Just needed to add the System.Web.Mvc.Html namespace to the using declaration (else html.RenderPartial(..) of course wont be accessible :))

Does anyone have this working with the RC of MVC2? They added an additional Textwriter parameter to ViewContext. I tried just adding a new StringWriter(), but it did not work.

@beckelmw: I updated the response. You must pass in the original StringWriter you are using to write to the StringBuilder, not a new instance or the output of the view will be lost.

asp.net mvc - Render a view as a string - Stack Overflow

asp.net-mvc rendering
Rectangle 27 27

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);

//...

There is no RenderPartial method on the HtmlHelper object. This is not possible - html.RenderPartial(viewName, viewData);

In ASP.NET MVC release 1.0 there are a couple of RenderPartial extension methods. The one I'm using in particular is System.Web.Mvc.Html.RenderPartialExtensions.RenderPartial(this HtmlHelper, string, object). I'm unaware whether the method has been added in the latest revisions of MVC and wasn't present in earlier ones.

Thanks. Just needed to add the System.Web.Mvc.Html namespace to the using declaration (else html.RenderPartial(..) of course wont be accessible :))

Does anyone have this working with the RC of MVC2? They added an additional Textwriter parameter to ViewContext. I tried just adding a new StringWriter(), but it did not work.

@beckelmw: I updated the response. You must pass in the original StringWriter you are using to write to the StringBuilder, not a new instance or the output of the view will be lost.

asp.net mvc - Render a view as a string - Stack Overflow

asp.net-mvc rendering
Rectangle 27 27

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);

//...

There is no RenderPartial method on the HtmlHelper object. This is not possible - html.RenderPartial(viewName, viewData);

In ASP.NET MVC release 1.0 there are a couple of RenderPartial extension methods. The one I'm using in particular is System.Web.Mvc.Html.RenderPartialExtensions.RenderPartial(this HtmlHelper, string, object). I'm unaware whether the method has been added in the latest revisions of MVC and wasn't present in earlier ones.

Thanks. Just needed to add the System.Web.Mvc.Html namespace to the using declaration (else html.RenderPartial(..) of course wont be accessible :))

Does anyone have this working with the RC of MVC2? They added an additional Textwriter parameter to ViewContext. I tried just adding a new StringWriter(), but it did not work.

@beckelmw: I updated the response. You must pass in the original StringWriter you are using to write to the StringBuilder, not a new instance or the output of the view will be lost.

asp.net mvc - Render a view as a string - Stack Overflow

asp.net-mvc rendering
Rectangle 27 27

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);

//...

There is no RenderPartial method on the HtmlHelper object. This is not possible - html.RenderPartial(viewName, viewData);

In ASP.NET MVC release 1.0 there are a couple of RenderPartial extension methods. The one I'm using in particular is System.Web.Mvc.Html.RenderPartialExtensions.RenderPartial(this HtmlHelper, string, object). I'm unaware whether the method has been added in the latest revisions of MVC and wasn't present in earlier ones.

Thanks. Just needed to add the System.Web.Mvc.Html namespace to the using declaration (else html.RenderPartial(..) of course wont be accessible :))

Does anyone have this working with the RC of MVC2? They added an additional Textwriter parameter to ViewContext. I tried just adding a new StringWriter(), but it did not work.

@beckelmw: I updated the response. You must pass in the original StringWriter you are using to write to the StringBuilder, not a new instance or the output of the view will be lost.

asp.net mvc - Render a view as a string - Stack Overflow

asp.net-mvc rendering
Rectangle 27 27

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);

//...

There is no RenderPartial method on the HtmlHelper object. This is not possible - html.RenderPartial(viewName, viewData);

In ASP.NET MVC release 1.0 there are a couple of RenderPartial extension methods. The one I'm using in particular is System.Web.Mvc.Html.RenderPartialExtensions.RenderPartial(this HtmlHelper, string, object). I'm unaware whether the method has been added in the latest revisions of MVC and wasn't present in earlier ones.

Thanks. Just needed to add the System.Web.Mvc.Html namespace to the using declaration (else html.RenderPartial(..) of course wont be accessible :))

Does anyone have this working with the RC of MVC2? They added an additional Textwriter parameter to ViewContext. I tried just adding a new StringWriter(), but it did not work.

@beckelmw: I updated the response. You must pass in the original StringWriter you are using to write to the StringBuilder, not a new instance or the output of the view will be lost.

asp.net mvc - Render a view as a string - Stack Overflow

asp.net-mvc rendering
Rectangle 27 27

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);

//...

There is no RenderPartial method on the HtmlHelper object. This is not possible - html.RenderPartial(viewName, viewData);

In ASP.NET MVC release 1.0 there are a couple of RenderPartial extension methods. The one I'm using in particular is System.Web.Mvc.Html.RenderPartialExtensions.RenderPartial(this HtmlHelper, string, object). I'm unaware whether the method has been added in the latest revisions of MVC and wasn't present in earlier ones.

Thanks. Just needed to add the System.Web.Mvc.Html namespace to the using declaration (else html.RenderPartial(..) of course wont be accessible :))

Does anyone have this working with the RC of MVC2? They added an additional Textwriter parameter to ViewContext. I tried just adding a new StringWriter(), but it did not work.

@beckelmw: I updated the response. You must pass in the original StringWriter you are using to write to the StringBuilder, not a new instance or the output of the view will be lost.

asp.net mvc - Render a view as a string - Stack Overflow

asp.net-mvc rendering
Rectangle 27 26

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);

//...

There is no RenderPartial method on the HtmlHelper object. This is not possible - html.RenderPartial(viewName, viewData);

In ASP.NET MVC release 1.0 there are a couple of RenderPartial extension methods. The one I'm using in particular is System.Web.Mvc.Html.RenderPartialExtensions.RenderPartial(this HtmlHelper, string, object). I'm unaware whether the method has been added in the latest revisions of MVC and wasn't present in earlier ones.

Thanks. Just needed to add the System.Web.Mvc.Html namespace to the using declaration (else html.RenderPartial(..) of course wont be accessible :))

Does anyone have this working with the RC of MVC2? They added an additional Textwriter parameter to ViewContext. I tried just adding a new StringWriter(), but it did not work.

@beckelmw: I updated the response. You must pass in the original StringWriter you are using to write to the StringBuilder, not a new instance or the output of the view will be lost.

asp.net mvc - Render a view as a string - Stack Overflow

asp.net-mvc rendering
Rectangle 27 8

System.Web.HttpException (0x80004005): Server cannot set status after HTTP headers have been sent.

I think the exception is because Response.End and Response.Redirect do not cause a thread abort in MVC applications (Response.Redirect is not really a part of the MVC pipeline).

return new RedirectResult("https://secure.mysite.com/account/signup", true);

asp.net mvc 4 - MVC4 - Server cannot set status after HTTP headers hav...

asp.net-mvc-4 redirect
Rectangle 27 1

The UpdatePanel is probably the problem here.

I get that. And I already have my imagebutton set to do a full postback. And it always works if there is no error encountered. The question is, why is the error messing things up for the next request and how do I resolve it while still keeping the update panel?

asp.net - Server cannot set content type after HTTP headers have been ...

asp.net http-headers updatepanel
Rectangle 27 1

You can use the following code in order to set a proper response. I believe you get your error because you are modifying the HttpContext response (however, do not quote me on that).

[HttpGet]
[Route("GenerateReport")]
public HttpResponseMessage GenerateReport()
{
    byte[] bytes = Generate();

    HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK);
    var stream = new MemoryStream(bytes);
    result.Content = new StreamContent(stream);
    result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");
    result.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
    {
        FileName = "test.pdf"
    };

    return result;
}

c# - Server cannot set content type after HTTP headers have been sent ...

c# asp.net-mvc-4
Rectangle 27 56

I'll broadly agree with Vagrant on the cause:

  • the stream was unbuffered forcing the response headers to get written before the markup writing could begin.
  • Your view encountered a runtime error
  • Fails because the headers have already been sent.

Where I disagree with Vagrant is the "cause no errors in binding" remedy - you could still encounter runtime errors in View binding e.g. null reference exceptions.

A better solution for this is to ensure that Response.BufferOutput = true; before any bytes are sent to the Response stream. e.g. in your controller action or On_Begin_Request in application. This enables server transfers, cookies/headers to be set etc. right the way up to naturally ending response, or calling end/flush.

Of course also check that buffer isn't being flushed/set to false further down in the stack too.

I get the same error but in my case it happens when I try to call a child action. I tried setting Response.BufferOutput = true at the beginning of the parent action but this didn't help. Any ideas?

Samo, somewhere earlier in your code something is writing bytes to the response stream, set buffering mu at the beginning of request processing e.g. before you let your Action begin in your controller.

asp.net mvc - Server cannot set status after HTTP headers have been se...

asp.net-mvc http iis-7
Rectangle 27 56

I'll broadly agree with Vagrant on the cause:

  • the stream was unbuffered forcing the response headers to get written before the markup writing could begin.
  • Your view encountered a runtime error
  • Fails because the headers have already been sent.

Where I disagree with Vagrant is the "cause no errors in binding" remedy - you could still encounter runtime errors in View binding e.g. null reference exceptions.

A better solution for this is to ensure that Response.BufferOutput = true; before any bytes are sent to the Response stream. e.g. in your controller action or On_Begin_Request in application. This enables server transfers, cookies/headers to be set etc. right the way up to naturally ending response, or calling end/flush.

Of course also check that buffer isn't being flushed/set to false further down in the stack too.

I get the same error but in my case it happens when I try to call a child action. I tried setting Response.BufferOutput = true at the beginning of the parent action but this didn't help. Any ideas?

Samo, somewhere earlier in your code something is writing bytes to the response stream, set buffering mu at the beginning of request processing e.g. before you let your Action begin in your controller.

asp.net mvc - Server cannot set status after HTTP headers have been se...

asp.net-mvc http iis-7
Rectangle 27 44

Just to add to the responses above. I had this same issue when i first started using ASP.Net MVC and i was doing a Response.Redirect during a controller action:

Response.Redirect("/blah", true);

Instead of returning a Response.Redirect action i should have been returning a RedirectAction:

return Redirect("/blah");

This is exactly what I was doing as well. Thanks for the fix.

Thanks, i was doing the same in my filter. Changed it and this got fixed... //Url helper to generate redirect url. UrlHelper urlHelper = new UrlHelper(filterContext.RequestContext); filterContext.Result = new RedirectResult(urlHelper.Action(ActionNames.Index, ControllerNames.CustomerSearch, new{Area = ""})); //at the end base.OnActionExecuting(filterContext);

I had a similar issue involving the .NET CAS Client and this answer clued me into my problem. I was essentially returning a response 'twice', calling CasAuthentication.SingleSignOut(); followed by a RedirectToAction(). Obviously this doesn't make sense -- how can you redirect twice, right? But I didn't realize it at the time. I changed my LogOut action return type from ActionResult to void, got rid of the Redirect, and the problem was solved. Thanks!

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Just to add to the responses above. I had this same issue when i first started using ASP.Net MVC and i was doing a Response.Redirect during a controller action:

Response.Redirect("/blah", true);

Instead of returning a Response.Redirect action i should have been returning a RedirectAction:

return Redirect("/blah");

This is exactly what I was doing as well. Thanks for the fix.

Thanks, i was doing the same in my filter. Changed it and this got fixed... //Url helper to generate redirect url. UrlHelper urlHelper = new UrlHelper(filterContext.RequestContext); filterContext.Result = new RedirectResult(urlHelper.Action(ActionNames.Index, ControllerNames.CustomerSearch, new{Area = ""})); //at the end base.OnActionExecuting(filterContext);

I had a similar issue involving the .NET CAS Client and this answer clued me into my problem. I was essentially returning a response 'twice', calling CasAuthentication.SingleSignOut(); followed by a RedirectToAction(). Obviously this doesn't make sense -- how can you redirect twice, right? But I didn't realize it at the time. I changed my LogOut action return type from ActionResult to void, got rid of the Redirect, and the problem was solved. Thanks!

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The HTTP server doesn't send the response header back to the client until you either specify an error or else you start sending data. If you start sending data back to the client, then the server has to send the response head (which contains the status code) first. Once the header has been sent, you can no longer put a status code in the header, obviously.

Here's the usual problem. You start up the page, and send some initial tags (i.e. <head>). The server then sends those tags to the client, after first sending the HTTP response header with an assumed SUCCESS status. Now you start working on the meat of the page and discover a problem. You can not send an error at this point because the response header, which would contain the error status, has already been sent.

The solution is this: Before you generate any content at all, check if there are going to be any errors. Only then, when you have assured that there will be no problems, can you then start sending content, like the tag.

In your case, it seems like you have a login page that processes a POST request from a form. You probably throw out some initial HTML, then check if the username and password are valid. Instead, you should authenticate the user/password first, before you generate any HTML at all.

asp.net mvc - Server cannot set status after HTTP headers have been se...

asp.net-mvc http iis-7
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The HTTP server doesn't send the response header back to the client until you either specify an error or else you start sending data. If you start sending data back to the client, then the server has to send the response head (which contains the status code) first. Once the header has been sent, you can no longer put a status code in the header, obviously.

Here's the usual problem. You start up the page, and send some initial tags (i.e. <head>). The server then sends those tags to the client, after first sending the HTTP response header with an assumed SUCCESS status. Now you start working on the meat of the page and discover a problem. You can not send an error at this point because the response header, which would contain the error status, has already been sent.

The solution is this: Before you generate any content at all, check if there are going to be any errors. Only then, when you have assured that there will be no problems, can you then start sending content, like the tag.

In your case, it seems like you have a login page that processes a POST request from a form. You probably throw out some initial HTML, then check if the username and password are valid. Instead, you should authenticate the user/password first, before you generate any HTML at all.

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Your OnActionExecution method sends the necessary redirection http headers, but It does not stop the controller code from executing.

I think you should use the following to redirect the user instead of Response.Redirect:

FilterContext.Result = new RedirectResult(url);

Thanks for your help, but i dnt solve the issue still the same error anyways i am marking the answer as helpful,...

I still think that the problems occurs because the CustomErrorHandleAttribute.cs is trying to send an http error after the redirection header has already been sent to the browser. You should probably debug what code runs after the redirection and what is the exact exception that is stored in the ExceptionContext.Exception

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Your OnActionExecution method sends the necessary redirection http headers, but It does not stop the controller code from executing.

I think you should use the following to redirect the user instead of Response.Redirect:

FilterContext.Result = new RedirectResult(url);

Thanks for your help, but i dnt solve the issue still the same error anyways i am marking the answer as helpful,...

I still think that the problems occurs because the CustomErrorHandleAttribute.cs is trying to send an http error after the redirection header has already been sent to the browser. You should probably debug what code runs after the redirection and what is the exact exception that is stored in the ExceptionContext.Exception

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StatusCode
Response.End
HandleUnauthorizedRequest
AuthorizeAttribute
var ctx = filterContext.HttpContext;
ctx.Response.StatusCode = (int)HttpStatusCode.Forbidden;
ctx.Response.End();

If you are using .NET 4.5+, add this line before Response.StatusCode

filterContext.HttpContext.Response.SuppressFormsAuthenticationRedirect = true;

asp.net mvc - Server cannot set status after HTTP headers have been se...

asp.net-mvc http iis-7