如果我启用智能模式，则会抛出 NullReferenceException

Question

我正在尝试将一组 PDF 合并在一起，并确保它们压缩得很好，并且没有重复的资源。但是，在我的代码中，如果我在编写器上调用 SetSmartMode(true)，第一次写入它总是会导致 NullReferenceException。

这是我的 (vb.net) 代码：

    Private Function CombinePdfBatch(pdfMetaData As IEnumerable(Of QuestDataSet.MetaDataRow), batchNumber As Integer,
                                 fileNamePrefix As String, outputDir As String) As String

    Dim outputFileName As String = Path.Combine(outputDir, fileNamePrefix & "_" & batchNumber & ".pdf")

    Using combinedPdf As New PdfDocument(New PdfWriter(Path.Combine(outputDir, fileNamePrefix & "_" & batchNumber & ".pdf")).SetSmartMode(True))

        'Make sure we close the underlying stream when we're done with the combination
        combinedPdf.SetCloseWriter(True)
        combinedPdf.SetCloseReader(False)
        combinedPdf.SetFlushUnusedObjects(False)
        combinedPdf.GetWriter().SetCompressionLevel(CompressionConstants.BEST_COMPRESSION)
        combinedPdf.GetWriter().SetCloseStream(True)
        combinedPdf.SetDefaultPageSize(New Geom.PageSize(630, 810))

        Dim merger As New PdfMerger(combinedPdf)

        For Each currentMD As QuestDataSet.MetaDataRow In pdfMetaData
            Using currentPDF As New PdfDocument(New PdfReader(Path.Combine(programPaths.Input, currentMD.ReceivedFilesRowByInputFileRelation.FileName)))
                currentPDF.SetCloseReader(True)
                currentPDF.SetCloseWriter(False)
                currentPDF.GetReader().SetCloseStream(True)

                currentMD.CombinedFileName = outputFileName
                currentMD.StartPage = combinedPdf.GetNumberOfPages() + 1
                merger.Merge(currentPDF, 1, currentPDF.GetNumberOfPages())
                currentMD.EndPage = combinedPdf.GetNumberOfPages()
            End Using
        Next
        merger.Close()            
    End Using

    Return outputFileName
End Function

一旦调用 merger.Merge，就会抛出 NullReferenceException。我已经用许多其他功能替换了它，但是如果在编写器处于智能模式时向 PDF 添加任何内容，它就会崩溃。

如果我禁用智能模式，PDF 将被合并。但是我需要尽可能地减小这些 PDF 的大小 而不会 牺牲太多质量。因为我知道他们都使用相同的字体并共享一些库存图片，所以我想我应该将它们全部组合起来才能做到这一点。

编辑：这是堆栈跟踪，因为我爱你们：

System.NullReferenceException occurred
  HResult=-2147467261
  Message=Object reference not set to an instance of an object.
  Source=itext.kernel
  StackTrace:
       at iText.Kernel.Pdf.PdfWriter.ByteStore.SerDic(PdfDictionary dic, Int32 level, ByteBufferOutputStream bb, IntHashtable serialized)
       at iText.Kernel.Pdf.PdfWriter.ByteStore.SerObject(PdfObject obj, Int32 level, ByteBufferOutputStream bb, IntHashtable serialized)
       at iText.Kernel.Pdf.PdfWriter.ByteStore..ctor(PdfStream str, IntHashtable serialized)
       at iText.Kernel.Pdf.PdfWriter.SmartCopyObject(PdfObject obj)    
       at iText.Kernel.Pdf.PdfWriter.CopyObject(PdfObject obj, PdfDocument document, Boolean allowDuplicating)
       at iText.Kernel.Pdf.PdfObject.ProcessCopying(PdfDocument documentTo, Boolean allowDuplicating)
       at iText.Kernel.Pdf.PdfArray.CopyContent(PdfObject from, PdfDocument document)
       at iText.Kernel.Pdf.PdfWriter.CopyObject(PdfObject obj, PdfDocument document, Boolean allowDuplicating)
       at iText.Kernel.Pdf.PdfObject.ProcessCopying(PdfDocument documentTo, Boolean allowDuplicating)
       at iText.Kernel.Pdf.PdfDictionary.CopyContent(PdfObject from, PdfDocument document)
       at iText.Kernel.Pdf.PdfWriter.CopyObject(PdfObject obj, PdfDocument document, Boolean allowDuplicating)
       at iText.Kernel.Pdf.PdfObject.ProcessCopying(PdfDocument documentTo, Boolean allowDuplicating)
       at iText.Kernel.Pdf.PdfObject.CopyTo(PdfDocument document, Boolean allowDuplicating)
       at iText.Kernel.Pdf.PdfDictionary.CopyTo(PdfDocument document, Boolean allowDuplicating)
       at iText.Kernel.Pdf.PdfDictionary.CopyTo(PdfDocument document, IList`1 excludeKeys, Boolean allowDuplicating)
       at iText.Kernel.Pdf.PdfPage.CopyTo(PdfDocument toDocument, IPdfPageExtraCopier copier)
       at iText.Kernel.Pdf.PdfDocument.CopyPagesTo(IList`1 pagesToCopy, PdfDocument toDocument, Int32 insertBeforePage, IPdfPageExtraCopier copier)
       at iText.Kernel.Pdf.PdfDocument.CopyPagesTo(IList`1 pagesToCopy, PdfDocument toDocument, IPdfPageExtraCopier copier)
       at iText.Kernel.Pdf.PdfDocument.CopyPagesTo(IList`1 pagesToCopy, PdfDocument toDocument)
       at iText.Kernel.Utils.PdfMerger.Merge(PdfDocument from, IList`1 pages)
       at iText.Kernel.Utils.PdfMerger.Merge(PdfDocument from, Int32 fromPage, Int32 toPage)
       at QuestMonolithic.Process.CombinePdfBatch(IEnumerable`1 pdfMetaData, Int32 batchNumber, String fileNamePrefix, String outputDir) in C:\Users\cchrist\Documents\Visual Studio 2012\Projects\Quest_Monolithic\trunk\source\Process.vb:line 594
  InnerException:

Answer 1

这是 iText 7 .NET 代码中的一个已知错误，很快就会部署修复程序。 SerDic() 方法仅在智能模式下复制时调用，它在 .NET 中错误地处理字典键的检索，导致空指针。

如果您想自己修复它，请将 itext.kernel.PdfWriter 中的第 592 行替换为：

dic.KeySet().ToArray(keys);

与

keys = dic.KeySet().ToArray(keys);

如果我启用智能模式，则会抛出 NullReferenceException

If I enable Smart Mode, a NullReferenceException is thrown

.net

vb.net

pdf

itext7