How do I get Gridview to render THEAD?

This should do it:

gv.HeaderRow.TableSection = TableRowSection.TableHeader;

The code in the answer needs to go on Page_Load or GridView_PreRender. I put it in a method that was called after Page_Load and got a NullReferenceException.

I use the following code to do this:

The if statements I added are important.

Otherwise (depending on how you render your grid) you'll throw exceptions like:

The table must contain row sections in order of header, body and then footer.

protected override void OnPreRender(EventArgs e)
{
    if ( (this.ShowHeader == true && this.Rows.Count > 0)
      || (this.ShowHeaderWhenEmpty == true))
    {
        //Force GridView to use <thead> instead of <tbody> - 11/03/2013 - MCR.
        this.HeaderRow.TableSection = TableRowSection.TableHeader;
    }
    if (this.ShowFooter == true && this.Rows.Count > 0)
    {
        //Force GridView to use <tfoot> instead of <tbody> - 11/03/2013 - MCR.
        this.FooterRow.TableSection = TableRowSection.TableFooter;
    }
    base.OnPreRender(e);
}

The this object is my GridView.

I actually overrode the Asp.net GridView to make my own custom control, but you could paste this into your aspx.cs page and reference the GridView by name instead of using the custom-gridview approach.

FYI: I haven't tested the footer logic, but I do know this works for Headers.

You can also use jQuery to add it. This avoids the problem with TableRowSection.TableHeader where gets dropped on PostBack.

$('#myTableId').prepend($("<thead></thead>").append($(this).find("#myTableId tr:first")));