iTextSharp GetInstance - NullReferenceException 错误

Question

希望有人能发现问题。 我正在将 DataGridView 保存为 PDF，并在下面的 GetInstance 代码行中出现错误。 我已经验证 sfd.FileName 具有有效值并且流不为空。

System.NullReferenceException: '未将对象引用设置为对象的实例。'

using (FileStream stream = new FileStream (sfd.FileName, FileMode.Create)) {

   iTextSharp.text.Document pdfDoc =  new iTextSharp.text.Document (PageSize.A4, 10f, 20f, 20f, 10f);

   PdfWriter.GetInstance (pdfDoc, stream);   // NullReferenceException on this line.
   pdfDoc.Open();
   pdfDoc.Add (pdfTable);
   pdfDoc.Close();
   stream.Close();
}

完整方法代码：

private void SavePDF () {

    if (grdKeywordSearch.Rows.Count > 0) {
        SaveFileDialog sfd = new SaveFileDialog();
        sfd.Filter = "PDF (*.pdf)|*.pdf";
        sfd.FileName = "Output.pdf";
        bool fileError = false;
        if (sfd.ShowDialog () == DialogResult.OK) {
            if (File.Exists (sfd.FileName)) {
                try {
                    File.Delete (sfd.FileName);
                } catch (IOException ex) {
                    fileError = true;
                    MessageBox.Show ("It wasn't possible to write the data to the disk." + ex.Message);
                }
            }
            if (!fileError) {
                try {
                    PdfPTable pdfTable = new PdfPTable (grdKeywordSearch.Columns.Count);
                    pdfTable.DefaultCell.Padding = 3;
                    pdfTable.WidthPercentage = 100;
                    pdfTable.HorizontalAlignment = Element.ALIGN_LEFT;

                    foreach (DataGridViewColumn column in grdKeywordSearch.Columns) {
                        PdfPCell cell = new PdfPCell(new Phrase(column.HeaderText));
                        pdfTable.AddCell (cell);
                    }

                    foreach (DataGridViewRow row in grdKeywordSearch.Rows) {
                        foreach (DataGridViewCell cell in row.Cells) {
                            pdfTable.AddCell (cell.Value.ToString());
                        }
                    }

                    using (FileStream stream = new FileStream (sfd.FileName, FileMode.Create)) {

                        iTextSharp.text.Document pdfDoc =  new iTextSharp.text.Document (PageSize.A4, 10f, 20f, 20f, 10f);

                        PdfWriter.GetInstance (pdfDoc, stream);
                        pdfDoc.Open();
                        pdfDoc.Add (pdfTable);
                        pdfDoc.Close();
                        stream.Close();
                    }

                    MessageBox.Show ("Data Exported Successfully.", "Info");
                } catch (Exception ex) {
                    MessageBox.Show ("Error :" + ex.Message);
                }
            }
        }
    } else {
        MessageBox.Show ("Nothing to export.", "Info");
    }

}

通过此代码添加的堆栈跟踪，错误前一行：

Console.WriteLine (new System.Diagnostics.StackTrace().ToString());

线程 0x4508 已退出，代码为 0 (0x0)。 线程 0x6078 已退出，代码为 0 (0x0)。 在 Clarity.frmClarity.SavePDF() 在 Clarity.frmClarity.btnSavePDF_Click(Object sender, EventArgs e) 在 System.Windows.Forms.Control.OnClick(EventArgs e) 在 System.Windows.Forms.Button.OnClick(EventArgs e) 在System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent) 在 System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks) 在 System.Windows.Forms.Control.WndProc(Message& m) 在 System. Windows.Forms.ButtonBase.WndProc(Message& m) at System.Windows.Forms.Button.WndProc(Message& m) at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) at System .Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
在 System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg) 在 System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData) 在 System.Windows .Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context) at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context) at Clarity.Program.Main()

Answer 1

我找到了解决方案，虽然我不明白。 您必须在调试选项下打开“仅我的代码”。 我这样做后错误就消失了。