c# – XMLWorker异常：未将对象引用设置为对象的实例

我想将html导出为pdf

var document = new Document();
 PdfWriter pdfWriter = PdfWriter.GetInstance(document,new FileStream("/my.pdf",FileMode.Create)); 
  pdfWriter.SetFullCompression();
  pdfWriter.StrictimageSequence = true;
  pdfWriter.SetLinearPageMode();

 var sr = new StringReader(htmlcode);
document.open();

var k = XMLWorkerHelper.GetInstance();
k.ParseXHtml(pdfWriter,document,sr);
//here it gave me an exception: Object reference not set to an instance of 
                                                                  an object


  sr.Close();
   document.Close();

Response.ContentType = "Application/pdf";
Response.AppendHeader("Content-disposition","attachment; filename="my.pdf");
Response.TransmitFile(@"c:\test\my.pdf");
Response.Flush();
Response.End();
Response.Close();

所有例外：

System.NullReferenceException: Object reference not set to an 
instance of an object.
       at iTextSharp.tool.xml.pipeline.html.HtmlPipeline.Close
                          (IWorkerContext context,Tag t,ProcessObject po)
       at iTextSharp.tool.xml.XMLWorker.EndElement(String tag,String ns)
       at iTextSharp.tool.xml.parser.XMLParser.EndElement()
    at iTextSharp.tool.xml.parser.state.ClosingTagState.Process(Char character)
       at iTextSharp.tool.xml.parser.XMLParser.ParseWithReader(TextReader reader)
       at iTextSharp.tool.xml.XMLWorkerHelper.ParseXHtml(PdfWriter writer,Document doc,TextReader inp)

解决方法

这一行出错

var k = XMLWorkerHelper.GetInstance();
k.ParseXHtml(pdfWriter,sr);

//这里它给了我一个例外：对象引用未设置为的实例
                                                                  一个东西

 由于任何一个输入参数的值指向NULL我们可以在传递之前检查它(变量将通过)是否为null或值.

以下代码足以获取HTML内容并将其写入PDF文件

Document pdfDoc = new Document(PageSize.A4,10,10);  
PdfWriter writer = PdfWriter.GetInstance(pdfDoc,new FileStream(@"D:\Syed\New PDF\PDF.pdf",FileMode.Create));// Output PDF File Path
Response.Write("File Created Successfully");
pdfDoc.open();
XMLWorkerHelper.GetInstance().ParseXHtml(writer,pdfDoc,new StreamReader(@"D:\Syed\test.html"));//This is input HTML file path
pdfDoc.Close();

它将从HTML文件中读取并将其写入创建的PDF文件中