iText7 convert HTML to PDF "System.NullReferenceException."

Question

iText7 convert HTML to PDF "System.NullReferenceException."

OLD TITLE: iTextSharp convert HTML to PDF "The document has no pages."

I am using iTextSharp and xmlworker to convert html from a view to PDF in ASP.NET Core 2.1

I tried many code snippets I found online but all generate an exception: "The document has no pages."

Here is my current code:

 public static byte[] ToPdf(string html)
 {

        byte[] output;
        using (var document = new Document())
        {
            using (var workStream = new MemoryStream())
            {
                PdfWriter writer = PdfWriter.GetInstance(document, workStream);
                writer.CloseStream = false;
                document.Open();
                using (var reader = new StringReader(html))
                {
                    XMLWorkerHelper.GetInstance().ParseXHtml(writer, document, reader);
                    document.Close();
                    output = workStream.ToArray();
                }
            }
        }
        return output;
 }

UPDATE 1

thanks to @Bruno Lowagie advice I upgraded to iText7 and pdfHTML , but I can't find much tutorials about it.

I tried this code:

 public static byte[] ToPdf(string html)
        {
             html = "<html><head><title>Extremely Basic Title</title></head><body>Extremely Basic Content</body></html>";


            byte[] output;

            using (var workStream = new MemoryStream())
            using (var pdfWriter = new PdfWriter(workStream))
            {
                using (var document = HtmlConverter.ConvertToDocument(html, pdfWriter))
                {
                    //Passes the document to a delegated function to perform some content, margin or page size manipulation
                    //pdfModifier(document);
                }

                //Returns the written-to MemoryStream containing the PDF.   
                return workStream.ToArray();
            }
        }

but I get System.NullReferenceException: when I call HtmlConverter.ConvertToDocument(html, pdfWriter)

Am I missing something?

UPDATE 2

I tried to debug using source code.

This is the stack trace

System.NullReferenceException
  HResult=0x80004003
  Message=Object reference not set to an instance of an object.
  Source=itext.io
  StackTrace:
   at iText.IO.Font.FontCache..cctor() in S:\Progetti\*****\itext7-dotnet-develop\itext\itext.io\itext\io\font\FontCache.cs:line 76

This is the code that generates the exception:

static FontCache() {
            try {
                LoadRegistry();
                foreach (String font in registryNames.Get(FONTS_PROP)) {
                    allCidFonts.Put(font, ReadFontProperties(font));
                }
            }
            catch (Exception) {
            }

registryNames count = 0 and .Get(FONTS_PROP) throws the exception

UPDATE 3

The problem was related due some sort of cache. I can't really understand what, but as you can see in the code the exceptions was generate when he tried to load fonts from cache. I realized that after having tried the same code to a new project and it worked.

so I cleaned the solution, deleted bin, obj, .vs, killed IIS Express, removed and reinstalled all nuget packages then run again, magically it worked.

then I had to made only a fix to the code: instead of HtmlConverter.ConvertToDocument that generates only 15 bytes document i used HtmlConverter.ConvertToPdf to generate a full pdf.

Here is the complete code:

public static byte[] ToPdf(string html)
{
    using (var workStream = new MemoryStream())
    {
        using (var pdfWriter = new PdfWriter(workStream))
        {                    
            HtmlConverter.ConvertToPdf(html, pdfWriter);
            return workStream.ToArray();
        }
    }
}

pdf

.net-core

itext

itext7

xmlworker

asked on Stack Overflow Jul 24, 2018 by

Stefano Balzarotti • edited Jul 25, 2018 by

Stefano Balzarotti

1 Answer

I had this EXACT same problem, and after digging down all the way to iText7's FontCache object and getting an error when trying to create my OWN FontProgram to use from a raw TTF file (which also failed with the same null reference error), I finally "solved" my problem.

Apparently iText has some internal errors/exceptions that they are just sort of "skipping" and "pushing past", because I realized by accident that I had "Enable Just My Code" in Visual Studios disabled, and so my system was trying to debug iText7's code as well as mine. The moment that I re-enabled it in my Visual Studio settings (Tools > Options > Debugging > General > Enable Just My Code checkbox), the problem magically went away.

So I spent four hours trying to troubleshoot a problem that was in THEIR code, but that they apparently found some way to work around and push through the method anyways even on a null reference failure.

My convert to PDF function is now working just fine.

answered on Stack Overflow May 26, 2021 by

Westley Bennett

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