START_PAGE 只制作第一页的标题

Question

我有这个用于 Web 开发的代码：

protected internal class MyEventHandler : iText.Kernel.Events.IEventHandler
{
    public virtual void HandleEvent(iText.Kernel.Events.Event @event)
    {
        iText.Kernel.Events.PdfDocumentEvent docEvent = 
                (iText.Kernel.Events.PdfDocumentEvent)@event;
        PdfDocument pdfDoc = docEvent.GetDocument();
    }

    public void onStartPage(
        iText.Kernel.Pdf.PdfWriter writer, iText.Layout.Document document)
    {
        // paragragrap for start pages
        …
    }
}

…

MyEventHandler StartPage = new MyEventHandler();
pdf.AddEventHandler(iText.Kernel.Events.PdfDocumentEvent.START_PAGE, new MyEventHandler());
StartPage.onStartPage(writer, document);

以及其他向页面添加更多内容的代码。 它只为第一页制作页眉。

Answer 1

您正在混合来自不同 iText 版本的事件处理。

在 iText 5 中，您曾经实现 IPdfPageEvent，通常是通过扩展 PdfPageEventHelper，而这里您有单独的方法，例如

void OnStartPage(PdfWriter writer, Document document)
void OnEndPage(PdfWriter writer, Document document)

等等

在 iText 7 中，您实现 IEventHandler，它只有一个方法，

void HandleEvent(Event @event)

您要么仅为一种事件类型注册事件处理程序，因此在HandleEvent 中知道正确的事件已到达，或者您根据事件类型 (@event.GetEventType()) 确定您获得并执行的事件类型相应的代码。

改变页面旋转的事件监听器示例

例如在this example 中，事件处理程序仅注册为页面启动

C07E01_EventHandlers.PageRotationEventHandler eventHandler = new PageRotationEventHandler();
pdf.AddEventHandler(PdfDocumentEvent.START_PAGE, eventHandler);

并在其事件处理方法中进行相应的操作

public virtual void HandleEvent(Event @event) {
    PdfDocumentEvent docEvent = (PdfDocumentEvent)@event;
    docEvent.GetPage().Put(PdfName.Rotate, this.rotation);
}

完整的示例类：

public class C07E01_EventHandlers {
    public const String DEST = "../../../results/chapter07/jekyll_hyde_page_orientation.pdf";

    public static readonly PdfNumber PORTRAIT = new PdfNumber(0);

    public static readonly PdfNumber LANDSCAPE = new PdfNumber(90);

    public static readonly PdfNumber INVERTEDPORTRAIT = new PdfNumber(180);

    public static readonly PdfNumber SEASCAPE = new PdfNumber(270);

    public static void Main(String[] args) {
        FileInfo file = new FileInfo(DEST);
        file.Directory.Create();
        new C07E01_EventHandlers().CreatePdf(DEST);
    }

    public virtual void CreatePdf(String dest) {
        PdfDocument pdf = new PdfDocument(new PdfWriter(dest));
        pdf.GetCatalog().SetPageLayout(PdfName.TwoColumnLeft);
        C07E01_EventHandlers.PageRotationEventHandler eventHandler = new PageRotationEventHandler();
        pdf.AddEventHandler(PdfDocumentEvent.START_PAGE, eventHandler);
        Document document = new Document(pdf, PageSize.A8);
        document.Add(new Paragraph("Dr. Jekyll"));
        eventHandler.SetRotation(INVERTEDPORTRAIT);
        document.Add(new AreaBreak());
        document.Add(new Paragraph("Mr. Hyde"));
        eventHandler.SetRotation(LANDSCAPE);
        document.Add(new AreaBreak());
        document.Add(new Paragraph("Dr. Jekyll"));
        eventHandler.SetRotation(SEASCAPE);
        document.Add(new AreaBreak());
        document.Add(new Paragraph("Mr. Hyde"));
        document.Close();
    }

    protected internal class PageRotationEventHandler : IEventHandler {
        protected internal PdfNumber rotation = C07E01_EventHandlers.PORTRAIT;

        public virtual void SetRotation(PdfNumber orientation) {
            this.rotation = orientation;
        }

        public virtual void HandleEvent(Event @event) {
            PdfDocumentEvent docEvent = (PdfDocumentEvent)@event;
            docEvent.GetPage().Put(PdfName.Rotate, this.rotation);
        }

        internal PageRotationEventHandler() {
        }
    }
}

添加页眉和页脚的示例页面监听器

在 cmets 中，您要求 标题示例而不是旋转页面。对于那个样子，例如在 iText 7 Jump-Start Tutorial 第 3 章 (Using renderers and event handlers) 示例 C03E03_UFO (Java version / C# version) 中使用事件侦听器添加背景、水印、页眉和页脚：

public class C03E03_UFO {

    internal static PdfFont helvetica = null;

    internal static PdfFont helveticaBold = null;

    public static void Main(String[] args) {
        helvetica = PdfFontFactory.CreateFont(StandardFonts.HELVETICA);
        helveticaBold = PdfFontFactory.CreateFont(StandardFonts.HELVETICA_BOLD);
        ...
    }

    protected internal virtual void CreatePdf(String dest) {
        //Initialize PDF document
        PdfDocument pdf = new PdfDocument(new PdfWriter(dest));
        pdf.AddEventHandler(PdfDocumentEvent.END_PAGE, new C03E03_UFO.MyEventHandler(this));
        ...
    }

    ...

    protected internal class MyEventHandler : IEventHandler {
        public virtual void HandleEvent(Event @event) {
            PdfDocumentEvent docEvent = (PdfDocumentEvent)@event;
            PdfDocument pdfDoc = docEvent.GetDocument();
            PdfPage page = docEvent.GetPage();
            int pageNumber = pdfDoc.GetPageNumber(page);
            Rectangle pageSize = page.GetPageSize();
            PdfCanvas pdfCanvas = new PdfCanvas(page.NewContentStreamBefore(), page.GetResources(), pdfDoc);
            //Set background
            Color limeColor = new DeviceCmyk(0.208f, 0, 0.584f, 0);
            Color blueColor = new DeviceCmyk(0.445f, 0.0546f, 0, 0.0667f);
            pdfCanvas.SaveState()
                     .SetFillColor(pageNumber % 2 == 1 ? limeColor : blueColor)
                     .Rectangle(pageSize.GetLeft(), pageSize.GetBottom(), pageSize.GetWidth(), pageSize.GetHeight())
                     .Fill()
                     .RestoreState();
            //Add header and footer
            pdfCanvas.BeginText()
                     .SetFontAndSize(C03E03_UFO.helvetica, 9)
                     .MoveText(pageSize.GetWidth() / 2 - 60, pageSize.GetTop() - 20)
                     .ShowText("THE TRUTH IS OUT THERE")
                     .MoveText(60, -pageSize.GetTop() + 30)
                     .ShowText(pageNumber.ToString())
                     .EndText();
            //Add watermark
            iText.Layout.Canvas canvas = new iText.Layout.Canvas(pdfCanvas, pdfDoc, page.GetPageSize());
            canvas.SetFontColor(ColorConstants.WHITE);
            canvas.SetProperty(Property.FONT_SIZE, UnitValue.CreatePointValue(60));
            canvas.SetProperty(Property.FONT, C03E03_UFO.helveticaBold);
            canvas.ShowTextAligned(new Paragraph("CONFIDENTIAL"), 298, 421, pdfDoc.GetPageNumber(page), TextAlignment.
                CENTER, VerticalAlignment.MIDDLE, 45);
            pdfCanvas.Release();
        }

        internal MyEventHandler(C03E03_UFO _enclosing) {
            this._enclosing = _enclosing;
        }

        private readonly C03E03_UFO _enclosing;
    }
}

严格来说，该示例监听的是 PdfDocumentEvent.END_PAGE 而不是 PdfDocumentEvent.START_PAGE。不过，这种差异应该不会造成太大影响。