将网格导出为pdf

我正在使用obout网格，并且尝试将网格导出为PDF，当我使用sqldatasource填充网格时，导出工作正常，但是当我使用存储过程和后面代码中的函数填充网格时，出现此错误

System.NullReferenceException：对象引用未设置为对象的实例

问题出在内部循环中

//How add the data from the Grid to pdf table
        for (int i = 0; i < Grid1.Rows.Count; i++)
        {
            Hashtable dataItem = Grid1.Rows[i].ToHashtable();

            foreach (Column col in Grid1.Columns)
            {

                    PdfPCell = new PdfPCell(new Phrase(new Chunk(dataItem[col.DataField].ToString(), font8)));
                    PdfPCell.RunDirection = PdfWriter.RUN_DIRECTION_LTR; //change the text direction for the arabic
                    PdfTable.AddCell(PdfPCell);

            }
        }

当我跟踪错误时，我注意到当到达最后一列时，它将继续读取不存在的另一列{Column}，这就是为什么我在此行中出现错误的原因

 PdfPCell = new PdfPCell(new Phrase(new Chunk(dataItem[col.DataField].ToString(), font8)));

哪个空

完整的代码

 private void ExportGridToPDF()
{       
    // Stream which will be used to render the data
    MemoryStream fileStream = new MemoryStream();

    Document doc = new Document(iTextSharp.text.PageSize.LETTER, 10, 10, 42, 35);
    try
    {            
        //Create Document class object and set its size to letter and give space left, right, Top, Bottom Margin
        PdfWriter wri = PdfWriter.GetInstance(doc, fileStream);

        doc.Open();//Open Document to write

        //Font font8 = FontFactory.GetFont("TAHOMA", 7);
        BaseFont bf = BaseFont.CreateFont("c:\\\\windows\\\\fonts\\\\tahoma.ttf", BaseFont.IDENTITY_H, true);
        iTextSharp.text.Font font8 = new iTextSharp.text.Font(bf, 8, iTextSharp.text.Font.NORMAL);

        //Write some content
        Paragraph paragraph = new Paragraph("ASP.NET Grid - Export to PDF");

        //Craete instance of the pdf table and set the number of column in that table
        PdfPTable PdfTable = new PdfPTable(Grid1.Columns.Count);
        PdfPCell PdfPCell = null;

        //Add headers of the pdf table
        foreach (Column col in Grid1.Columns)
        {                
            PdfPCell = new PdfPCell(new Phrase(new Chunk(col.HeaderText, font8)));
            PdfPCell.RunDirection = PdfWriter.RUN_DIRECTION_LTR; //change the text direction for the arabic               
            PdfTable.AddCell(PdfPCell);
        }

        //How add the data from the Grid to pdf table
        for (int i = 0; i < Grid1.Rows.Count; i++)
        {
            Hashtable dataItem = Grid1.Rows[i].ToHashtable();

            foreach (Column col in Grid1.Columns)
            {

                    PdfPCell = new PdfPCell(new Phrase(new Chunk(dataItem[col.DataField].ToString(), font8)));
                    PdfPCell.RunDirection = PdfWriter.RUN_DIRECTION_LTR; //change the text direction for the arabic
                    PdfTable.AddCell(PdfPCell);

            }
        }

        PdfTable.SpacingBefore = 15f;

        doc.Add(paragraph);
        doc.Add(PdfTable);
    }
    catch (DocumentException docEx)
    {
        //handle pdf document exception if any
        MessageBox.Show(docEx.ToString());
    }
    catch (IOException ioEx)
    {
        // handle IO exception
        MessageBox.Show(ioEx.ToString());
    }
    catch (Exception ex)
    {
        // ahndle other exception if occurs
        MessageBox.Show(ex.ToString());
    }
    finally
    {
        //Close document and writer
        doc.Close();
    }

    // Send the data and the appropriate headers to the browser
    Response.Clear();
    Response.AddHeader("content-disposition", "attachment;filename=oboutGrid.pdf");
    Response.ContentType = "application/pdf";
    Response.BinaryWrite(fileStream.ToArray());
    Response.End(); 
}

任何建议