Document.NewPage使对象引用未设置为对象的实例

Question

我是创建pdfs的新手，并成功地使用了一个但没有页脚，所以我一直在寻找并基于this

这是我的代码：

string nome = "MapaAnual" + DateTime.Now.Year.ToString() + "_" + DateTime.Now.Month.ToString() + "" + DateTime.Now.Day.ToString() + ".pdf";
string outputFile = "C:\\Users\\sies4578\\Documents\\Visual Studio 2012\\Projects\\ULSM_Equipamentos\\REL\\" + nome.ToString();
try
{
    //Create a standard .Net FileStream for the file, setting various flags
    //FileStream fs = new FileStream(outputFile, FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.ReadWrite);
    System.IO.FileStream fs = new System.IO.FileStream(outputFile + DateTime.Now.ToString("ddMMyyHHmmss") + ".pdf", System.IO.FileMode.OpenOrCreate);

    //Create a new PDF document setting the size to A4
    Document doc = new Document(PageSize.A4.Rotate());

    //Bind the PDF document to the FileStream using an iTextSharp PdfWriter
    PdfWriter w = PdfWriter.GetInstance(doc, fs);

    w.PageEvent = new MyPageEventHandler();
    //Open the document for writing
    doc.Open();
    for (int i = 0; i < listaServicos.Count; i++)
    {
        doc.NewPage(); //where it goes to the catch giving that error

        #region Calibracoes

        //Code that doesn't matter
        #endregion
    }
    doc.Close();
    Process.Start(outputFile);
    return "PDF criado com sucesso";
}
catch (Exception ex)
{
    Console.WriteLine("An error ocurred, the PDF-document could not be created.");
    return ex.Message;
}

我怀疑它是否相关，但这里要问的是MyPageEventHandler的代码：

    public class MyPageEventHandler : iTextSharp.text.pdf.PdfPageEventHelper
    {
        // This is the contentbyte object of the writer
        PdfContentByte cb;

        // we will put the final number of pages in a template
        PdfTemplate template;

        // this is the BaseFont we are going to use for the header / footer
        BaseFont bf = null;

        // This keeps track of the creation time
        DateTime PrintTime = DateTime.Now;
        protected iTextSharp.text.Font footer
        {
            get
            {
                // create a basecolor to use for the footer iTextSharp.text.Font, if needed.
                BaseColor grey = new BaseColor(128, 128, 128);
                iTextSharp.text.Font font = iTextSharp.text.FontFactory.GetFont("Arial", 9, iTextSharp.text.Font.NORMAL, grey);
                return font;
            }
        }

        public override void OnStartPage(PdfWriter writer, Document doc)
        {
            //Inicio Cabeçalho Logo
            //Inicio Cabeçalho Logo
            PdfPTable cabecalho = new PdfPTable(3);
            cabecalho.DefaultCell.Border = 0;
            cabecalho.DefaultCell.HorizontalAlignment = Element.ALIGN_CENTER;
            cabecalho.TotalWidth = 700;
            float[] width1 = { 150.0F, 550.0F, 550.0F };
            cabecalho.SetWidths(width1);
            cabecalho.LockedWidth = true;
            iTextSharp.text.Image im = iTextSharp.text.Image.GetInstance("C:\\ULSMatosinhos\\Software\\ULS-Matosinhos\\Images\\logopro.png");
            cabecalho.AddCell(im);
            iTextSharp.text.Font cabeca = new iTextSharp.text.Font(iTextSharp.text.FontFactory.GetFont("arial", 14, iTextSharp.text.Font.BOLDITALIC, new BaseColor(23, 181, 150)));
            PdfPCell linha = new PdfPCell(new Phrase("PLANO DE CALIBRAÇÕES - " + anoCalibracao.ToString(), cabeca));
            linha.Border = 0;
            linha.HorizontalAlignment = 1;
            linha.VerticalAlignment = Element.ALIGN_MIDDLE;
            cabecalho.AddCell(linha);

            iTextSharp.text.Font cd = new iTextSharp.text.Font(iTextSharp.text.FontFactory.GetFont("arial", 8, iTextSharp.text.Font.NORMAL, BaseColor.BLACK));
            PdfPCell codigoDoc = new PdfPCell(new Phrase(" 591_00_SIE_1191", cd));
            codigoDoc.Border = 0;
            codigoDoc.HorizontalAlignment = 1;
            codigoDoc.VerticalAlignment = Element.ALIGN_MIDDLE;
            cabecalho.AddCell(codigoDoc);
            doc.Add(cabecalho);
        }
        public override void OnEndPage(PdfWriter writer, Document document)
        {
            base.OnEndPage(writer, document);

            int pageN = writer.PageNumber;
            String text = "Page " + pageN + " of ";
            float len = bf.GetWidthPoint(text, 8);

            iTextSharp.text.Rectangle pageSize = document.PageSize;

            cb.SetRGBColorFill(100, 100, 100);

            cb.BeginText();
            cb.SetFontAndSize(bf, 8);
            cb.SetTextMatrix(pageSize.GetLeft(40), pageSize.GetBottom(30));
            cb.ShowText(text);
            cb.EndText();

            cb.AddTemplate(template, pageSize.GetLeft(40) + len, pageSize.GetBottom(30));

            cb.BeginText();
            cb.SetFontAndSize(bf, 8);
            cb.ShowTextAligned(PdfContentByte.ALIGN_RIGHT,
                "Printed On " + PrintTime.ToString(),
                pageSize.GetRight(40),
                pageSize.GetBottom(30), 0);
            cb.EndText();
        }

        public override void OnCloseDocument(PdfWriter writer, Document document)
        {
            base.OnCloseDocument(writer, document);

            template.BeginText();
            template.SetFontAndSize(bf, 8);
            template.SetTextMatrix(0, 0);
            template.ShowText("" + (writer.PageNumber - 1));
            template.EndText();
        }
    }