bind value to a Textbox in Gridview header

I am using a gridview in aspx page. I am adding Textboxes dynamically to the griview header. How can I insert a value to the textbox in the grid header. My code goes like

protected void GridView1_RowCreated(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.Header)
    {
    TextBox txtBox1 = default(TextBox);
    for (int i = 0; i <= (e.Row.Cells.Count - 1); i++)
        {
        litHeader.Text = e.Row开发者_如何学运维.Cells[i].Text + "<br/>";
        e.Row.Cells[i].Controls.Add(litHeader);                                   
        e.Row.Cells[i].Controls.Add(txtBox1); 
    }
    }
} 

I am trying to bind a value to the textbox 'txtBox1' using the code

private void FillGridView()
 {
    TextBox txt;
    txt = (TextBox)GridView1.HeaderRow.FindControl("txtBox1");
    txt.Text = dtValues.Rows[0][5].ToString();
 }

But I am not able to fill the textbox. Please help.

---

This may help someone on very old question. This how I update my header row text box immediately after I insert data to GV1. Hope it helps.

    protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {

        if (e.Row.RowType == DataControlRowType.DataRow)
        {

        }


        if (e.Row.RowType == DataControlRowType.Header)
        {
            //((TextBox)GridView1.HeaderRow.FindControl("tbProjNumInsert")).Text
            if (newMaxNum != null && newMaxNum.Length > 0)
            {                
           ((TextBox)e.Row.Cells[4].FindControl("tbProjNumInsert")).Text = newMaxNum;
           System.Diagnostics.Debug.WriteLine("GridView1_RowDataBound()...GridView1.Width !!!! " + ((TextBox)e.Row.Cells[4].FindControl("tbProjNumInsert")).Text + "........newMaxNum:" + newMaxNum);
            }
        }

    }