Question

我正在尝试将aspx页面导出为pdf。我在Button2_Click上使用此代码，但我在htmlworker.Parse（str）上采用了System.NullReferenceException;：

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();

Answer 1

虽然可以直接写入Response.OutputStream，但这样做有时会掩盖错误。相反，我真的建议您写入另一个流，例如FileStream或MemoryStream。如果使用后者，则还可以将MemoryStream保存到可以在函数之间传递的字节数组中。下面的代码显示了这个以及在一次性物体上使用配置模式。

//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();

根据您渲染控件的方式，上面的内容可能仍会中断。您可能会收到一条消息，上面写着：

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

您可以通过覆盖网页的VerifyRenderingInServerForm方法来解决此问题。

public override void VerifyRenderingInServerForm(Control control) {
}

Answer 2

您的HTML是否包含<hr>标记？它在HTMLworker中不受支持。

Answer 3

我有类似的问题。我发现自己将HTMLTagProcessors提供给HTMLWorker可以解决这个问题。

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

现在，HTMLWorker支持一些HTML标记。

Itextsharp导出为pdf NullReferenceException

3 个答案: