public void chk_CheckedChanged(object sender, System.EventArgs e)
{
CheckBox chk = this.GetHeaderCheckBox(this.GridView1);
foreach (GridViewRow i in this.GridView1.Rows)
{
CheckBox inChk = (CheckBox)i.Cells[0].Controls[1];
inChk.Checked = chk.Checked;
}
}

protected void GridView1_RowCreated(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType.ToString().Equals("Header"))
{
this.txt_code.Text = e.Row.RowType.ToString();
CheckBox chk = (CheckBox)e.Row.Cells[0].Controls[1];
chk.CheckedChanged += new EventHandler(chk_CheckedChanged);
}
}