Can someone explain what are iTextEvents in ItextSharp? - events

Question

Can someone explain what are iTextEvents in ItextSharp..
I have found a bunch of codes with its use but i dont get how they works..
Im asking you if anyone can explain me these:
OnOpenDocument
OnEndPage
OnCloseDocument

Answer 1

If you are looking to start using iText, then your question is obsolete. You are referring to a concept that was used in versions 5 and earlier of iText for .NET (we abandoned the name iTextSharp a long time ago). If you want to start using iText for .NET, you should start with version 7, not with iText 5 or earlier, because we stopped development on those versions. Any release we make now is nothing more than a maintenance release (maintenance releases don't contain new functionality, they have bug fixes that are meant for paying users who can't migrate to iText 7 immediately).
The name page events was misleading because those events were initially used to allow developers to execute code when a new page was created or finalized, but as the code grew organically, we also started to use the page event functionality for other things, such as: to add special behavior of a Chunk (OnGenericTag()) or to execute code before or after adding a Paragraph. That was an example of bad design.
We fixed this bad design in iText 7, where we introduced renderers and event handlers. See chapter 3 of the jump-start tutorial, entitled Using renderers and event handlers.
In iText 7, we can create an event handler such as:
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.SetProperty(Property.FONT_COLOR, Color.WHITE);
canvas.SetProperty(Property.FONT_SIZE, 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();
}
}
The event handler is introduced in the code like this:
PdfDocument pdf = new PdfDocument(new PdfWriter(dest));
pdf.AddEventHandler(PdfDocumentEvent.END_PAGE, new C03E03_UFO.MyEventHandler(this));
// Initialize document
Document document = new Document(pdf);
Paragraph p = new Paragraph("List of reported UFO sightings in 20th century").SetTextAlignment(TextAlignment
.CENTER).SetFont(helveticaBold).SetFontSize(14);
document.Add(p);
Table table = new Table(new float[] { 3, 5, 7, 4 });
table.SetWidth(UnitValue.CreatePercentValue(100));
StreamReader sr = File.OpenText(DATA);
String line = sr.ReadLine();
Process(table, line, helveticaBold, true);
while ((line = sr.ReadLine()) != null) {
Process(table, line, helvetica, false);
}
sr.Close();
document.Add(table);
document.Close();
This code adds a background, a watermark, a header, and a footer, as is shown in this figure:
Page events in "iTextSharp" had a similar purpose, but you shouldn't use them anymore. They are outdated. You should use iText 7 instead.
If you posted your question out of historical curiosity, you should search old questions on Stack Overflow, such as:
How can I add an image to all pages of my PDF?
itextsharp: How to generate a report with dynamic header in PDF using itextsharp?
Change the color of pdf pages alternatively using iText pdf in java
How to introduce multiple PdfPageEventHelper instances?
...