how to export all data in pdf format using datalist

hi...all of you

 

i am trying to export all data in datalist in Pdf format . but i get error Object reference not set to an instance of an object.

this line  htmlparser.Parse(sr);

 

so all my code is 

 

using (StringWriter sw = new StringWriter())
{
using (HtmlTextWriter hw = new HtmlTextWriter(sw))
{

this.GetList();
datalistToallMem.RenderControl(hw);
StringReader sr = new StringReader(sw.ToString());
Document pdfDoc = new Document(PageSize.A2, 10f, 10f, 10f, 0f);
HTMLWorker htmlparser = new HTMLWorker(pdfDoc);
PdfWriter.GetInstance(pdfDoc, Response.OutputStream);
pdfDoc.Open();
htmlparser.Parse(sr);
pdfDoc.Close();
Response.ContentType = "application/pdf";
Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.pdf");
Response.Cache.SetCacheability(HttpCacheability.NoCache);
Response.Write(pdfDoc);
Response.End();
}
}