PageEvent 抛出 Cannot access a closed Stream

Question

添加PageEvent生成Header和Footer时，关闭后好像在尝试写入stream。我不确定将页面事件放在哪里。如果我删除页面事件，它会生成 pdf 文件。

p.Parse(html); 是 "Cannot access a closed Stream" 失败的地方。删除 writer.PageEvent 将导致 Parse 工作，但它不会生成 header/footer.

我使用 this 页面作为 header/footer 代码的参考。

代码：

try {
  using(var stream = new MemoryStream()) {
    using(var document = new Document(PageSize.LETTER, 20 f, 20 f, 5 f, 5 f)) {
      using(var writer = PdfWriter.GetInstance(document, stream)) {
        HtmlPipelineContext htmlContext = new HtmlPipelineContext(null);
        writer.PageEvent = new HeaderFooter(Header, Footer); // if I remove this it generates fine but then I don't get a header/footer.

        var tagProcessors = (DefaultTagProcessorFactory) Tags.GetHtmlTagProcessorFactory();
        tagProcessors.RemoveProcessor(HTML.Tag.IMG); // remove the default processor
        tagProcessors.AddProcessor(HTML.Tag.IMG, new CustomImageTagProcessor()); // use our new processor
        htmlContext.SetTagFactory(tagProcessors);

        ICSSResolver CssResolver = XMLWorkerHelper.GetInstance().GetDefaultCssResolver(true);
        CssResolver.AddCss(Css, true);
        IPipeline pipeline =
         new CssResolverPipeline(CssResolver,
          new HtmlPipeline(htmlContext,
           new PdfWriterPipeline(document, writer)));

        XMLWorker worker = new XMLWorker(pipeline, true);

        XMLParser p = new XMLParser(worker);

        document.Open();

        using(var html = new StringReader(HtmlData)) {
         p.Parse(html);  // <-- ERROR thrown here
        }
       // close document   tried docoment.Close();  same issue
      }
    }

  // get bytes from stream  
  pdf = stream.ToArray();
 }
}

页面事件如下：

public class HeaderFooter: PdfPageEventHelper {
 protected ElementList header;
 protected ElementList footer;
 private string _footerText;
 private string _headerText;

 public HeaderFooter(string headerText, string footerText) {
  header = XMLWorkerHelper.ParseToElementList(headerText, null);
  footer = XMLWorkerHelper.ParseToElementList(footerText, "table { font-size: 8px; font-style: italic; }");
  _footerText = footerText;
  _headerText = headerText;
 }

 public override void OnEndPage(PdfWriter writer, Document document) {

  try {

   footer = XMLWorkerHelper.ParseToElementList(_footerText.Replace("@PageNumber", writer.PageNumber.ToString()), "table { font-size: 8px; font-style: italic; }");
   ColumnText ct = new ColumnText(writer.DirectContent);
   ct.SetSimpleColumn(new Rectangle(36, 832, 559, 810));
   foreach(IElement e in header) {
    ct.AddElement(e);
   }
   ct.Go();
   ct.SetSimpleColumn(new Rectangle(36, 10, 559, 32));

   foreach(IElement e in footer) {
    ct.AddElement(e);
   }
   ct.Go();



  } catch (DocumentException de) {
   throw new Exception();
  }
 }
}

Answer 1

在将 PdfWriter 放入 using 语句之前曾遇到过类似问题。这是一个基于您的问题的简化示例，您可以测试以重现该问题：

// ObjectDisposedException: Cannot access a closed Stream.
using (var stream = new MemoryStream())
{
    using (var document = new Document())
    {
        using (var writer = PdfWriter.GetInstance(document, stream))
        {
            document.Open();
            document.Add(new Chunk("test"));
        }
    }
    pdf = stream.ToArray();
}

该代码片段抛出 ObjectDisposedException：无法访问已关闭的流。 如您所述。

相反，如果 PdfWriter 是 Dispose() 这样的：

PdfWriter writer = null;
try
{
    using (var stream = new MemoryStream())
    {
        using (var document = new Document())
        {
            writer = PdfWriter.GetInstance(document, stream);
            document.Open();
            document.Add(new Chunk("test"));
        }
        pdf = stream.ToArray();
    }
}
finally { writer.Dispose(); }

一切顺利。 iTextSharp v5.5.8.

Answer 2

这原来是正在使用的 html 的问题。尽管页面在没有 header 的情况下生成的 PDF 完全正常，但在添加 header 时它会失败。使用和 returns 都很好。

PageEvent 抛出 Cannot access a closed Stream

PageEvent is throwing Cannot access a closed Stream

c#

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