Itextsharp：添加新线型时如何避免替换现有线型？

Question

I'm generating a clothing label as pdfs using iText. I'm trying to add a dashed line as a folding line in every page. But when I added a dashed line existing strokes replace to dashed lines? Any idea how to stop this?

I tried adding dashed lines when creating the pdf and after creating the pdf. But none of those works.

This is my code.

string inputPDF = "C:\\Users\\User\\Documents\\visual studio 2017\\Projects\\iTextSharpExample\\iTextSharpExample\\pdf\\Label_dynamicLive_SampleTemplate.pdf";
string outputPDF = "C:\\Users\\User\\Documents\\visual studio 2017\\Projects\\iTextSharpExample\\iTextSharpExample\\pdf\\Label_dynamicLive_SampleTemplate_foldline.pdf";
PdfReader reader = new PdfReader(inputPDF);

using (var fileStream = new FileStream(outputPDF, FileMode.Create, FileAccess.Write))
{
    var document = new Document(reader.GetPageSizeWithRotation(1));
    var writer = PdfWriter.GetInstance(document, fileStream);

    document.Open();

    for (var i = 1; i <= reader.NumberOfPages; i++)
    {
        document.NewPage();

        var baseFont = BaseFont.CreateFont(BaseFont.HELVETICA_BOLD, BaseFont.CP1252, BaseFont.NOT_EMBEDDED);
        var importedPage = writer.GetImportedPage(reader, i);

        var contentByte = writer.DirectContent;

    //line start
    float moveto_x = 0 + 1;
    float lineto_x = 20 - 1;
    float moveto_y = (110 / 2) + 5;
    float lineto_y = (110 / 2) + 5;

    float moveto_x2 = 0 + 1;
    float lineto_x2 = 20 - 1;
    float moveto_y2 = (110 / 2) - 5;
    float lineto_y2 = (110 / 2) - 5;


    float lineWidth = 0.5f;
    float unitsOn = 5;
    float unitsOff = 1;
    float phase = 2;

    moveto_x = iTextSharp.text.Utilities.MillimetersToPoints(moveto_x);
    moveto_y = iTextSharp.text.Utilities.MillimetersToPoints(moveto_y);
    contentByte.MoveTo(moveto_x, moveto_y);
    lineto_x = iTextSharp.text.Utilities.MillimetersToPoints(lineto_x);
    lineto_y = iTextSharp.text.Utilities.MillimetersToPoints(lineto_y);
    contentByte.LineTo(lineto_x, lineto_y);
    contentByte.SetLineWidth(lineWidth);
    contentByte.SetLineDash(unitsOn, unitsOff, phase);
    contentByte.Stroke();
    //line end



    contentByte.AddTemplate(importedPage, 0, 0);
    }

    document.Close();
    writer.Close();
}

I expected to write dashed lines in every page in given ordinates. But it turned to replace straight lines to dashed lines. Any idea how to add a lines without replacing existing?

Answer 1

The line dash (just like the line width, fill and stroke colors, and many other properties) is part of the "pdf graphics state".

To get back an earlier graphics state, pdfs support a stack of graphics states. When the current state is what you want to get back to later, you push the current state on that stack. And when you want to get back to that state, you pop it off of that stack.

The instruction for pushing is called save-state, the instruction for popping restore-state. The matching PdfContentByte methods are SaveState() and RestoreState() .

Thus, start with contentByte.SaveState() , then do your stuff, then end with contentByte.RestoreState() .

---

Add an aside, your code generates instructions in an invalid order:

contentByte.MoveTo(moveto_x, moveto_y);
contentByte.LineTo(lineto_x, lineto_y);
contentByte.SetLineWidth(lineWidth);
contentByte.SetLineDash(unitsOn, unitsOff, phase);
contentByte.Stroke();

Here you first create a path, then set line width and line dash, and then stroke the path. Strictly speaking, though, between the creation of a path and the instruction drawing it there may at most be an instruction to combine the path with the clip path but nothing else.

Most pdf viewers don't insist on that, though, so you'll probably not have concrete problems because of that.

But if your pdfs are validated, this invalid order may be reported as error.

Thus, first set the parameters, then create the path and draw it.

contentByte.SaveState();
contentByte.SetLineWidth(lineWidth);
contentByte.SetLineDash(unitsOn, unitsOff, phase);
contentByte.MoveTo(moveto_x, moveto_y);
contentByte.LineTo(lineto_x, lineto_y);
contentByte.Stroke();
contentByte.RestoreState();