How to add a table as a header?

I am working with iTextSharp trying to add an header and a footer to my generated PDF but, if I try to add an header that have width of 100% of my page I have some problem.

So I have do the following things:

1) I have create a class named PdfHeaderFooter that extends the iTextSharp PdfPageEventHelper class

2) Into PdfHeaderFooter I have implemented the OnStartPage() method that generate the header:

    // write on start of each page
    public override void OnStartPage(PdfWriter writer, Document document)
    {
        base.OnStartPage(writer, document);
        PdfPTable tabHead = new PdfPTable(new float[] { 1F });
        PdfPCell cell;
        //tabHead.TotalWidth = 300F;
        tabHead.WidthPercentage = 100;

        cell = new PdfPCell(new Phrase("Header"));
        tabHead.AddCell(cell);
        tabHead.WriteSelectedRows(0, -1, 150, document.Top, writer.DirectContent);
    }

If I use sometning like tabHead.TotalWidth = 300F; insted tabHead.WidthPercentage = 100; it work well but if I try to set as 100% the width of the tabHead table (as I do in the previous example) when it call the tabHead.WriteSelectedRows(0, -1, 150, document.Top, writer.DirectContent) method it throw the following exception:

The table width must be greater than zero.

Why? What is the problem? How is it possible that the table have 0 size if I am setting it to 100%?

Someone can help me to solve this issue?

Tnx

When using writeSelectedRows(), it doesn't make sense to set the width percentage to 100%. Setting the width percentage is meant for when you add a document using document.add() (which is a method you can't use in a page event). When using document.add(), iText calculates the width of the table based on the page size and the margins.

You are using writeSelectedRows(), which means you are responsible to define the size and the coordinates of the table.

If you want the table to span the complete width of the page, you need:

table.TotalWidth = document.Right - document.Left;

You're also using the wrong X-coordinate: you should use document.Left instead of 150.

Additional info:

The first two parameters define the start row and the end row. In your case, you start with row 0 which is the first row, and you don't define an end row (that's what -1 means) in which case all rows are drawn.
You omitted the parameters for the columns (there's a variation of the writeSelectedRows() that expects 7 parameters).
Next you have the X and Y value of start coordinate for the table.
Finally, you pass a PdfContentByte instance. This is the canvas on which you're drawing the table.