iTextSharp 7对象引用未设置为对象的实例 [英] iTextSharp 7 object reference not set to an instance of an object
问题描述
是否有建议使用包含段落的单元格来构建表格，以避免在将某些单元格添加到表格或表格到文档时出现异常？我得到了这个，我无法弄清楚会发生什么：
Is there some recommendation to build tables with cells having paragraphs in order to avoid an exception at adding of some cell to table or table to document? I get this and I can't figure out what happens:
[NullReferenceException: Object reference not set to an instance of an object.]
iText.Layout.Renderer.TableRenderer.DrawBorders(DrawContext drawContext) +2493
iText.Layout.Renderer.TableRenderer.DrawChildren(DrawContext drawContext) +1497
iText.Layout.Renderer.AbstractRenderer.Draw(DrawContext drawContext) +153
iText.Layout.Renderer.TableRenderer.Draw(DrawContext drawContext) +637
iText.Layout.Renderer.AbstractRenderer.DrawChildren(DrawContext drawContext) +104
iText.Layout.Renderer.BlockRenderer.Draw(DrawContext drawContext) +525
iText.Layout.Renderer.TableRenderer.DrawChildren(DrawContext drawContext) +1382
iText.Layout.Renderer.AbstractRenderer.Draw(DrawContext drawContext) +153
iText.Layout.Renderer.TableRenderer.Draw(DrawContext drawContext) +637
iText.Layout.Renderer.DocumentRenderer.FlushSingleRenderer(IRenderer resultRenderer) +473
iText.Layout.Renderer.RootRenderer.AddChild(IRenderer renderer) +1999
iText.Layout.RootElement`1.Add(BlockElement`1 element) +92
iText.Layout.Document.Add(BlockElement`1 element) +81
这是一个简单的快照（与真正的项目）使用Windows控制台项目：
Here is a simple snapshot (compared to the real project) using a Windows console project:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using iText.Layout;
using iText.Layout.Borders;
using iText.Layout.Element;
namespace iTextTest
{
public static class iTextSharpHelper
{
public static T SetBorderEx<T>(this ElementPropertyContainer<T> element, Border border)
where T : ElementPropertyContainer<T>
{
element.SetBorder(border);
return (T)element;
}
public static Paragraph Style(this BlockElement<Paragraph> element)
{
element
.SetBorderEx(iText.Layout.Borders.Border.NO_BORDER)
.SetFont(iText.Kernel.Font.PdfFontFactory.CreateFont(iText.IO.Font.FontConstants.HELVETICA))
.SetFontSize(10.0f)
.SetFixedLeading(12.0f)
.SetVerticalAlignment(iText.Layout.Properties.VerticalAlignment.BOTTOM)
.SetMargin(0f);
return (Paragraph)element;
}
}
class Program
{
private static float[] tableColumns = { 0.35f, 0.25f, 0.15f, 0.25f };
static void Main(string[] args)
{
iText.Kernel.Pdf.PdfDocument pdf = new iText.Kernel.Pdf.PdfDocument(new iText.Kernel.Pdf.PdfWriter("test.pdf"));
iText.Layout.Document document = new iText.Layout.Document(pdf, iText.Kernel.Geom.PageSize.A4);
document.SetMargins(50f, 50f, 25f, 50f);
iText.Layout.Element.Table mainTable = new iText.Layout.Element.Table(tableColumns)
.SetBorderEx(iText.Layout.Borders.Border.NO_BORDER)
.SetWidthPercent(100)
.SetHorizontalAlignment(iText.Layout.Properties.HorizontalAlignment.LEFT)
.SetPadding(0f);
for (int i = 0; i < 10; i++)
{
AddRow(mainTable, "ABCDEFGHIJ", "ABCDEFGHIJ", "ABCDEFGHIJ");
}
document.Add(mainTable);
document.Close();
}
private static void AddRow(iText.Layout.Element.Table table, string col1, string col2, string col3)
{
// Label
AddCell(table, col1, true)
.SetBorderTop(new iText.Layout.Borders.SolidBorder(iText.Kernel.Colors.Color.BLACK, 0.5f));
// Product - Voucher and price/pcs
AddCell(table, col2, true)
.SetBorderTop(new iText.Layout.Borders.SolidBorder(iText.Kernel.Colors.Color.BLACK, 0.5f));
// Message
AddCell(table, col3, true, 2)
.SetBorderTop(new iText.Layout.Borders.SolidBorder(iText.Kernel.Colors.Color.BLACK, 0.5f))
//.SetBorderRight(new iText.Layout.Borders.SolidBorder(iText.Kernel.Colors.Color.BLACK, 0.5f))
.SetHorizontalAlignment(iText.Layout.Properties.HorizontalAlignment.RIGHT)
.SetTextAlignment(iText.Layout.Properties.TextAlignment.RIGHT);
}
private static iText.Layout.Element.Cell AddCell(iText.Layout.Element.Table table, string text, bool setBold = false, int colSpan = 1)
{
iText.Layout.Element.Cell cell = new iText.Layout.Element.Cell(1, colSpan)
.SetBorderEx(iText.Layout.Borders.Border.NO_BORDER)
.SetVerticalAlignment(iText.Layout.Properties.VerticalAlignment.BOTTOM);
if (!string.IsNullOrEmpty(text))
{
iText.Layout.Element.Paragraph paragraph = new iText.Layout.Element.Paragraph(text)
.Style();
if (setBold)
paragraph.SetBold();
cell.Add(paragraph);
}
table.AddCell(cell);
return cell;
}
}
}
注意，注释掉一行代码：
Note, a commented out line of code:
//.SetBorderRight(new iText.Layout.Borders.SolidBorder(iText.Kernel.Colors.Color.BLACK, 0.5f))
添加它可以作为一种解决方法，使文档呈现而没有例外。
Adding it serves as a workaround to make the document render without the exception.
推荐答案
鉴于OP添加的示例代码，可轻松复制该问题。
Given the sample code added by the OP the issue can easily be reproduced.
此外，在将代码移植到iText / Java后，问题也可以在那里重现，参见 MikesTableIssue .java 测试方法 testMikesCode 。因此，从Java（原始的iText代码）到C＃没有移植错误。
Furthermore after porting the code to iText/Java the issue could be reproduced there, too, cf. MikesTableIssue.java test method testMikesCode. Thus, it is no porting error from Java (the original iText code) to C#.
样本甚至可以大大简化并仍然重现问题：
The sample could even be considerably simplified and still reproduce the issue:
try ( FileOutputStream target = new FileOutputStream("mikesTableIssueSimple.pdf");
PdfWriter pdfWriter = new PdfWriter(target);
PdfDocument pdfDocument = new PdfDocument(pdfWriter) )
{
Document document = new Document(pdfDocument);
Table mainTable = new Table(1);
Cell cell = new Cell()
.setBorder(Border.NO_BORDER)
//.setBorderRight(new SolidBorder(Color.BLACK, 0.5f))
.setBorderTop(new SolidBorder(Color.BLACK, 0.5f));
cell.add("TESCHTINK");
mainTable.addCell(cell);
document.add(mainTable);
}
（ MikesTableIssue.java测试方法 testSimplified ）
如果一个
- 删除
setBorder（Border.NO_BORDER）或 - 删除
setBorderTop（new SolidBorder（Color.BLACK，0.5f））或 - 添加
setBorderRight（new SolidBorder（Color.BLACK，0.5f） ））。
- removes
setBorder(Border.NO_BORDER)or - removes
setBorderTop(new SolidBorder(Color.BLACK, 0.5f))or - adds
setBorderRight(new SolidBorder(Color.BLACK, 0.5f)).
在这种情况下 com.itextpdf.layout.renderer。 TableRenderer.drawBorders（DrawContext）执行此代码：
In this situation com.itextpdf.layout.renderer.TableRenderer.drawBorders(DrawContext) executes this code:
if (lastBorder != null) {
if (verticalBorders.get(j).size() > 0) {
if (i == 0) {
x2 += verticalBorders.get(j).get(i).getWidth() / 2;
} else if(i == horizontalBorders.size() - 1 && verticalBorders.get(j).size() >= i - 1 && verticalBorders.get(j).get(i - 1) != null) {
x2 += verticalBorders.get(j).get(i - 1).getWidth() / 2;
}
}
lastBorder.drawCellBorder(drawContext.getCanvas(), x1, y1, x2, y1);
}
而 lastBorder 是 SolidBorder 实例， verticalBorders 是 [[null]，[null]] ， j == 1 和 i == 0 。
因此，这里应该引入一些额外的 null 检查。
Thus, some additional null checks ought to be introduced here.
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