iTextSharp Storing barcodes as Elements - Null reference exception - asp.net-mvc

Question

Im working on a class that will render PDF documents on an intranet web server. The problem that I am having is that iTextSharp uses the PDFWriter to render the barcode images and I am trying to build a collection of IElements before I render the document. Is there a way to create a collection that incorporates barcode images or is there a better way to code this class?
Hopefully my code can explain it better. Thanks.
public class PDFDoc
{
public float Width { get; set; }
public float Height { get; set; }
private List<IElement> Elements { get; set;}
...
private MemoryStream ms = new MemoryStream();
private Document doc = new Document();
private PdfWriter writer;
private void initializeDocument()
{
doc = new Document(new Rectangle(Width, Height), marginLeft, marginRight, marginTop, marginBottom);
writer = PdfWriter.GetInstance(doc, ms);
Elements = new List<IElement>();
}
private FileStreamResult GenerateLabel(IEnumerable<IElement> elements)
{
doc.Open();
foreach (var e in elements)
{
doc.Add(e);
}
//doc.Add(GenerateBarcodeImage("123456")); //GenBC works here but not below
writer.CloseStream = false;
doc.Close();
byte[] byteinfo = ms.ToArray();
ms.Write(byteinfo, 0, byteinfo.Length);
ms.Position = 0;
ms.Seek(0, SeekOrigin.Begin);
return new FileStreamResult(ms, "application/pdf");
}
private Image GenerateBarcodeImage(string code)
{
Barcode128 code128 = new Barcode128();
code128.Code = code;
code128.X = 1f;
return code128.CreateImageWithBarcode(new PdfContentByte(writer), null, null);
}
//Program
public FileStreamResult RenderLabel()
{
Elements.Add(new Paragraph("This is a test"));
Elements.Add(GenerateBarcodeImage("123456")); //This gives a null ref exception.
return GenerateLabel(Elements);
}

Answer 1

The problem with the code snippet is that you're trying to access the MemoryStream after calling Document.Close(). You can move the Close() call below you call ms.ToArray(), or do away with the MemoryStream entirely.
When you instantiate a PdfWriter, you can use any available Stream, so why not use Response.OutputStream:
List<IElement> Elements = new List<IElement>();
using (Document document = new Document()) {
PdfWriter writer = PdfWriter.GetInstance(
document, Response.OutputStream
);
document.Open();
PdfContentByte cb = writer.DirectContent;
for (int i = 0; i < 9; ++i) {
Barcode128 code128 = new Barcode128();
code128.Code = "code " + i.ToString();
Elements.Add(code128.CreateImageWithBarcode(cb, null, null));
}
for (int i = 0; i < Elements.Count; ++i) {
document.Add(new Paragraph("Barcode: " + i.ToString()));
document.Add(Elements[i]);
}
}