Select / Deselect all checkbox in gridview

We can select and deselect checkbox in gridview in onPostback event of checkbox in gridview header.

protected void CheckBox2_CheckedChanged(object sender, System.EventArgs e)
{
GridViewRow gv = default(GridViewRow);

CheckBox chkH = (CheckBox)GridView1.HeaderRow.FindControl("CheckBox2");

if (chkH.Checked == true) {

foreach ( gv in GridView1.Rows) {
CheckBox chk = (CheckBox)GridView1.Rows(gv.RowIndex).FindControl("CheckBox1");
chk.Checked = true;
}
} else {

foreach ( gv in GridView1.Rows) {
CheckBox chk = (CheckBox)GridView1.Rows(gv.RowIndex).FindControl("CheckBox1");
chk.Checked = false;
}

}
}