关闭文档时调用IText7结束页事件

如前所述 earlier answer IText 7页面事件会被延迟触发 -不过,通常不会像您在问题标题中假定的那样,直到文档关闭,而是页面 N+ 1 在page事件发生之前可能已经快完成了 n 已处理。

因此,设置 新建页眉 作为事件处理程序的属性,还必须告诉事件处理程序何时开始使用它。所以…

改进的处理程序

protected class ImprovedVariableHeaderEventHandler : IEventHandler
{
    Dictionary<PdfPage, String> headers = new Dictionary<PdfPage, string>();
    protected String header = "";

    public void setHeaderFor(String header, PdfPage page)
    {
        headers[page] = header;
    }

    public void HandleEvent(Event @event)
    {
        PdfDocumentEvent documentEvent = (PdfDocumentEvent)@event;
        PdfPage page = documentEvent.GetPage();
        if (headers.ContainsKey(page))
        {
            header = headers[page];
            headers.Remove(page);
        }
        new PdfCanvas(page)
                .BeginText()
                .SetFontAndSize(PdfFontFactory.CreateFont(StandardFonts.HELVETICA), 12)
                .MoveText(450, 806)
                .ShowText(header)
                .EndText()
                .Stroke();
    }
}

这个改进的处理程序可以这样使用:

PdfDocument pdfDoc = new PdfDocument(new PdfWriter(dest));
Document doc = new Document(pdfDoc, PageSize.A4, true);
ImprovedVariableHeaderEventHandler handler = new ImprovedVariableHeaderEventHandler();
pdfDoc.AddEventHandler(PdfDocumentEvent.END_PAGE, handler);
List<int> factors;
for (int i = 2; i < 40; i++)
{
    if (2 != i)
    {
        doc.Add(new AreaBreak());
    }

    factors = getFactors(i);
    if (factors.Count == 1)
    {
        doc.Add(new Paragraph("This is a prime number!"));
    }
    foreach (int factor in factors)
    {
        doc.Add(new Paragraph("Factor: " + factor));
    }

    handler.setHeaderFor(String.Format("THE FACTORS OF {0}", i), pdfDoc.GetLastPage());
}
doc.Close();

结果是您期望的输出。

具有多个标题元素的变体

我们可能不想为了那么少的内容浪费那么多的页面。在这种情况下,多个数字的因式分解应该放在一个页面上,我们希望在标题中提到所有这些数字。这可以通过使用类似以下的替代事件侦听器来实现:

protected class ImprovedVariableHeaderEventHandlerAlt : IEventHandler
{
    Dictionary<PdfPage, String> headers = new Dictionary<PdfPage, string>();
    protected String header = "";

    public void addHeaderDetailFor(string header, PdfPage page)
    {
        if (headers.ContainsKey(page))
            headers[page] += ", " + header;
        else
            headers[page] = header;
    }

    public void HandleEvent(Event @event)
    {
        PdfDocumentEvent documentEvent = (PdfDocumentEvent)@event;
        PdfPage page = documentEvent.GetPage();
        if (headers.ContainsKey(page))
        {
            header = String.Format("THE FACTORS OF {0}", headers[page]);
            headers.Remove(page);
        }
        new PdfCanvas(page)
                .BeginText()
                .SetFontAndSize(PdfFontFactory.CreateFont(StandardFonts.HELVETICA), 12)
                .MoveText(150, 806)
                .ShowText(header)
                .EndText()
                .Stroke();
    }
}

使用此代码:

PdfDocument pdfDoc = new PdfDocument(new PdfWriter(dest));
Document doc = new Document(pdfDoc, PageSize.A4, true);
ImprovedVariableHeaderEventHandlerAlt handler = new ImprovedVariableHeaderEventHandlerAlt();
pdfDoc.AddEventHandler(PdfDocumentEvent.END_PAGE, handler);
List<int> factors;
for (int i = 2; i < 40; i++)
{
    doc.Add(new Paragraph(String.Format("The factors of {0}", i)).SetBold());
    handler.addHeaderDetailFor(i.ToString(), pdfDoc.GetLastPage());

    factors = getFactors(i);
    if (factors.Count == 1)
    {
        doc.Add(new Paragraph("This is a prime number!"));
    }
    foreach (int factor in factors)
    {
        doc.Add(new Paragraph("Factor: " + factor));
    }
}
doc.Close();

通过在为一个新数字绘制节头之后立即通知事件侦听器,该数字将在打印此节头的页的页头中提到,而实际的因子分解可能在下一页中。