c# - PdfContentByte.SetFontAndSize() 抛出 "Object reference not set to instance of object"

Question

我正在尝试添加一个文本框注释，其文本具有指定的字体和大小。代码如下:

void addTextBox(string inputPath,string outputPath)
{
    PdfReader pdfReader = new PdfReader(inputPath);
    PdfStamper pdfStamper = new PdfStamper(pdfReader, new FileStream(outputPath, FileMode.Create));
    PdfContentByte pcb = new PdfContentByte(pdfStamper.Writer);
    BaseFont baseFont = FontFactory.GetFont(FontFactory.HELVETICA).BaseFont;
    float fontsize = 32;
    pcb.SetFontAndSize(baseFont, fontsize);
    PdfAnnotation textbox = PdfAnnotation.CreateFreeText(pdfStamper.Writer, new iTextSharp.text.Rectangle(200, 200, 3000, 3000), "Here is a Textbox", pcb);
    pdfStamper.AddAnnotation(textbox, 1);
    pdfStamper.Close();
}

pcb.SetFontAndSize() 调用抛出异常:

Object reference not set to an instance of an object.

pcb 发生此错误时已实例化，并且 fontsize 已成功分配其数值，那么这里未分配的对象是什么？

Answer 1

将 PdfContentByte(pdfStamper.Writer) 替换为 pdfStamper.GetOverContent(1)，问题就会消失。