Itextsharp export to pdf NullReferenceException

问题

I am trying to export the aspx page to pdf. I am using this code on Button2_Click, but i take a System.NullReferenceException on htmlworker.Parse(str);:

string attachment = "attachment; filename=Article.pdf";

Response.ClearContent();
Response.AddHeader("content-disposition", attachment);
Response.ContentType = "application/pdf";

StringWriter stw = new StringWriter();
HtmlTextWriter htextw = new HtmlTextWriter(stw);
dvText.RenderControl(htextw);
Document document = new Document();
PdfWriter.GetInstance(document, Response.OutputStream);

document.Open();
StringReader str = new StringReader(stw.ToString());
HTMLWorker htmlworker = new HTMLWorker(document);
htmlworker.Parse(str);
document.Close();

Response.Write(document);
Response.End();

回答1:

Although you can write directly to the Response.OutputStream, doing so can mask errors sometimes. Instead I really recommend that you write to another stream such as a FileStream or MemoryStream. If you use the latter you can also then persist the MemoryStream to a byte array that you can pass between functions. The code below shows this off as well as using the dispose pattern on disposable objects.

//We'll use this byte array as an intermediary later
Byte[] bytes;

//Basic setup for iTextSharp to write to a MemoryStream, nothing special
using (var ms = new MemoryStream()) {
    using (var document = new Document()) {
        using (var writer = PdfWriter.GetInstance(document, ms)) {
            document.Open();

            //Create our HTML worker (deprecated by the way)
            HTMLWorker htmlworker = new HTMLWorker(document);

            //Render our control
            using (var stw = new StringWriter()) {
                using (var htextw = new HtmlTextWriter(stw)) {
                    GridView1.RenderControl(htextw);
                }
                using (var str = new StringReader(stw.ToString())) {
                    htmlworker.Parse(str);
                }
            }

            //Close the PDF
            document.Close();
        }
    }
    //Get the raw bytes of the PDF
    bytes = ms.ToArray();
}

//At this point all PDF work is complete and we only have to deal with the raw bytes themselves
string attachment = "attachment; filename=Article.pdf";
Response.ClearContent();
Response.AddHeader("content-disposition", attachment);
Response.ContentType = "application/pdf";
Response.BinaryWrite(bytes);
Response.End();

The above may still break on you depending on how you are rendering your control. You might receive a message saying something like:

Control 'xxx' of type 'yyy' must be placed inside a form tag with runat=server

You can get around this by overriding the page's VerifyRenderingInServerForm method.

public override void VerifyRenderingInServerForm(Control control) {
}

回答2:

Does your HTML contain <hr> tag? It's not supported in HTMLworker.

回答3:

I have similar problem. I can find myself that giving HTMLTagProcessors to HTMLWorker solves this problem.

HTMLWorker htmlworker = new HTMLWorker(document, new HTMLTagProcessors(), null);

Now some HTML tags are supported by HTMLWorker.

来源：https://stackoverflow.com/questions/17167842/itextsharp-export-to-pdf-nullreferenceexception

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