iTextSharp - Adding content to a cell later in the code - itext

Question

I am using iTextSharp to generate an invoice PDF. For that I wish to display order number and total amount at top of PDF. However the actual amount is calculated during product displaying part.
To make it simple the report follows this structure
===========order number=========
===========total amount=========
//here I display the products and so total amount is calculated here.
==========end of report=========
To achieve this I am creating a cell for total amount like this
PdfPCell cell = new PdfPCell();
PdfPCell headingAmountCell = cell;
//add some components to cell, reinitialize them again with new cells etc.
//but still have first cell reference in headingAmountCell
//calculate total amount here.
.
.
.
.
headerAmountCell.AddElement(new Phrase("Total Amount:" + totalAmount.ToString());
.
.
.
However this doesn't work.
I can see order number at top but not total amount.
If you could please help, that'll be great.
Thanks in anticipation.
Regards
Anshul
UPDATE:
Here is a small portion of code to help understand the problem
//header
var headerTable = new PdfPTable(logoExists ? 2 : 1);
headerTable.WidthPercentage = 100f;
if (logoExists)
headerTable.SetWidths(new[] { 50, 50 });
float padding = 5f;
//logo
if (logoExists)
{
var logoFilePath = _pictureService.GetPictureUrl(logoPicture, 0, false);
var cellLogo = new PdfPCell(Image.GetInstance(logoFilePath));
cellLogo.Border = Rectangle.BOTTOM_BORDER;
cellLogo.BorderColorBottom = BaseColor.GRAY;
cellLogo.PaddingBottom = padding;
cellLogo.VerticalAlignment = Rectangle.ALIGN_TOP;
headerTable.AddCell(cellLogo);
}
//store info
var cell = new PdfPCell();
cell.Border = Rectangle.BOTTOM_BORDER;
cell.BorderColorBottom = BaseColor.GRAY;
cell.PaddingBottom = padding;
cell.HorizontalAlignment = Element.ALIGN_RIGHT;
cell.VerticalAlignment = Element.ALIGN_TOP;
//payment method
var paymentMethod = _paymentService.LoadPaymentMethodBySystemName(order.PaymentMethodSystemName);
string paymentMethodStr = paymentMethod != null ? paymentMethod.GetLocalizedFriendlyName(_localizationService, lang.Id) : order.PaymentMethodSystemName;
PdfPCell headingAmountCell = cell;
if (!paymentMethodStr.Contains("COD") && order.PaymentStatus == global::Nop.Core.Domain.Payments.PaymentStatus.Paid)
{
cell.AddElement(new Paragraph("PREPAID", bigFont));
}
else if (paymentMethodStr.Contains("COD") && order.PaymentStatus == global::Nop.Core.Domain.Payments.PaymentStatus.Paid)
{
cell.AddElement(new Phrase("PAYMENT COLLECTED ON DELIVERY", bigFont));
}
else
{
cell.AddElement(new Paragraph("COLLECT ON DELIVERY", bigFont));
}
string order_number = order.GetOrderNumber();
cell.AddElement(new Paragraph(String.Format(_localizationService.GetResource("PDFInvoice.Order#", lang.Id), order_number), bigFont));
var store = _storeService.GetStoreById(order.StoreId) ?? _storeContext.CurrentStore;
cell.AddElement(new Paragraph(String.Format("Order Date: {0}", _dateTimeHelper.ConvertToUserTime(order.CreatedOnUtc, DateTimeKind.Utc).ToString("D", new CultureInfo(lang.LanguageCulture))), font));
headerTable.AddCell(cell);
doc.Add(headerTable);
//THEN I PERFORM SOME PRODUCT DISPLAY PART WHERE I CALCULATE THE ORDERTOTAL THEN AT THE BOTTOM
//.
//.
..
headingAmountCell.AddElement(new Phrase(Math.Round(orderTotal) + "<-AMOUNT TO COLLECT")));