Question

MVC 3. VB.NET I have the following controller action in my application to send generated PDF files to the User by download. The function works fine when the controller itself has been invoked. But when I call to the function from outside the controller it returns a ” Object reference not set to an instance of an object ” error as soon as it hits the response.contenttype line. I have verified that all of the variables are in fact making it to the below action… But no dice if I try to call this in another controller:

   Dim _print as new PrintController
   _print.showUserPDF(firstName,lastName)
   return RedirectToAction("Registrants")

the function in the PrintController that is throwing the error is:

   Function showUserPDF(ByVal pdfName As String, ByVal fileName As String, ByVal _directory As String) As ActionResult
        If Not String.IsNullOrEmpty(pdfName) Then
            Response.ContentType = "application/pdf"
            Response.AppendHeader("Content-Disposition", "attachment; filename=" + fileName)
            Response.TransmitFile(pdfName)
            Response.[End]()

            Dim FileToDelete As String

            FileToDelete = pdfName

            If System.IO.File.Exists(FileToDelete) = True Then
                System.IO.File.Delete(FileToDelete)
            End If

            Directory.Delete(_directory)
            Return Nothing
        End If
        Return Nothing

    End Function

any ideas why this is only working when called explicitly from inside its containing controller???

Answer 1

Clearly there is no Response object set on the method when called from another controller, nor should there be if (a) it’s not being created by the MVC framework or (b) you aren’t explicitly populating the HttpContext property via the ControllerContext. This is really the wrong way to go about both downloading content and sharing code between two controllers.

First, you should be using a FileResult, using the signature that takes a byte array since you might delete the file, to deliver a file as a download from a controller. The FileResult is explicitly designed to do this. You should not be writing directly to the Response from your controller as that violates the separation of concerns fundamental to MVC.

Second, to share the code you should abstract the code to a shared base controller from which both derive or a helper class, preferably the former. That way you will have the method available directly in the controller created by the framework and won’t need to instantiate another controller just to invoke the method.

Last, you can’t both deliver a file to download AND redirect in the same response. You might want to handle this client-side via javascript if this is required. Note the file download should leave you on the same page.

_{I apologize in advance for any syntax or other errors. I read VB better than I write it}

Public Class ExtendedControllerBase
    Inherits Controller

    Function showUserPDF(ByVal pdfName As String, ByVal fileName As String, ByVal _directory As String) As ActionResult
            If Not String.IsNullOrEmpty(pdfName) Then

                Dim input As New FileStream(pdfName, FileMode.Open)
                Dim bytes(CInt(input.Length - 1)) As Byte
                input.Read(bytes, 0, CInt(input.Length))

                Dim FileToDelete As String

                FileToDelete = pdfName

                If System.IO.File.Exists(FileToDelete) = True Then
                    System.IO.File.Delete(FileToDelete)
                End If

                Directory.Delete(_directory)
                Return File( bytes, "application/pdf", fileName )
            End If
            Return Content("") 'You might want to throw an exception here?

        End Function
End Class

Public Class PrintController
    Inherits ExtendedBaseController

    ...

End Class