我正在尝试将带有 id 的图像插入 PDF 文档，并允许稍后用另一个图像替换它。我的流程如下：
- 从客户端获取图像（具有唯一 ID）。
- 尝试在 PDF 文档中查找具有相同 ID 的现有图像。
- 如果我找到现有图像，请尝试将其删除并放置新图像，或者尝试用新图像替换现有图像。（都试过了）。
- 如果我没有找到现有图像，请将图像插入我选择的位置。
我使用 Bruno Lowagie 书中的代码：
问题是每当我删除现有图像或替换它时，我的文档都会损坏。我究竟做错了什么？这是代码：
public static bool PdfInsertSignature(string path, string fileName, string signatureName, byte[] imageBytes)
{
bool resultOk = true;
string tmpFilename = string.Concat("tmp_", Guid.NewGuid().ToString(), ".pdf");
// get file, copy to new file with signature
using (Stream inputPdfStream = new FileStream(path + fileName, FileMode.Open, FileAccess.Read, FileShare.Read))
using (Stream outputPdfStream = new FileStream(path + tmpFilename, FileMode.Create, FileAccess.Write, FileShare.None))
{
using (var reader = new PdfReader(inputPdfStream))
using (PdfStamper stamper = new PdfStamper(reader, outputPdfStream, '\0', false))
{
var img = System.Drawing.Image.FromStream(new MemoryStream(imageBytes));
Image image = Image.GetInstance(img, BaseColor.WHITE);
img.Dispose();
var positions = stamper.AcroFields.GetFieldPositions(signatureName)[0];
if (positions != null)
{
//DeleteExistingSignatureImage(reader, stamper, signatureName);
image.SetAbsolutePosition(positions.position.Left + 20, positions.position.Top - 15);
image.ScalePercent(0.2f * 100);
image.BorderWidth = 0;
PdfImage pdfImg = new PdfImage(image, "", null);
pdfImg.Put(new PdfName("ITXT_SigImageId"), new PdfName(signatureName + "_img"));
if (!ReplaceImage(reader, stamper, signatureName, pdfImg))
{
PdfIndirectObject objRef = stamper.Writer.AddToBody(pdfImg);
image.DirectReference = objRef.IndirectReference;
PdfContentByte pdfContentByte = stamper.GetOverContent(positions.page);
pdfContentByte.AddImage(image);
}
}
else
{
resultOk = false;
logger.Error($"No matching Signature found for signatureName: {signatureName} in fileName: {fileName}.");
}
}
}
if (resultOk)
{
// delete old file and rename new file to old file's name
File.Delete(path + fileName);
File.Move(path + tmpFilename, path + fileName);
}
else
{
File.Delete(path + tmpFilename);
}
return resultOk;
}
private static bool ReplaceImage(PdfReader reader, PdfStamper stamper, string signatureName, PdfStream newImgStream)
{
PdfName key = new PdfName("ITXT_SigImageId");
PdfName value = new PdfName(signatureName + "_img");
PdfObject obj;
PRStream stream;
for (int i = 1; i < reader.XrefSize; i++)
{
obj = reader.GetPdfObject(i);
if (obj == null || !obj.IsStream())
{
continue;
}
stream = (PRStream)obj;
PdfObject pdfSubtype = stream.Get(PdfName.SUBTYPE);
if (pdfSubtype != null && pdfSubtype.ToString().Equals(PdfName.IMAGE.ToString()))
{
var streamVal = stream.Get(key);
if (streamVal != null && value.Equals(streamVal))
{
stream.Clear();
var ms = new MemoryStream();
stream.WriteContent(ms);
stream.SetData(ms.ToArray(), false);
foreach (PdfName name in newImgStream.Keys)
{
stream.Put(name, stream.Get(name));
}
return true;
}
}
}
return false;
}
private static void DeleteExistingSignatureImage(PdfReader reader, PdfStamper stamper, string signatureName)
{
PdfName key = new PdfName("ITXT_SigImageId");
PdfName value = new PdfName(signatureName + "_img");
PdfObject obj;
PRStream stream;
for (int i = 1; i < reader.XrefSize; i++)
{
obj = reader.GetPdfObject(i);
if (obj == null || !obj.IsStream())
{
continue;
}
stream = (PRStream)obj;
PdfObject pdfSubtype = stream.Get(PdfName.SUBTYPE);
if (pdfSubtype != null && pdfSubtype.ToString().Equals(PdfName.IMAGE.ToString()))
{
var streamVal = stream.Get(key);
if (streamVal != null && value.Equals(streamVal))
{
stream.Clear();
PdfReader.KillIndirect(stream);
//PdfReader.KillIndirect(obj);
//reader.RemoveUnusedObjects();
}
}
}
}