Gridveiw contain templatefield as textbox value is not retriving. Its giving null value

foreach (GridViewRow items in OrderItemsGrid.Rows)
            {

                 //int.Parse(items.Cells[0].Text);
                 itemid =     Convert.ToInt32(((Label)items.FindControl("lblItemId")).Text);
                TextBox txt = (TextBox)items.FindControl("TxtQuantity");
                //txt.ID = "txt" + "_" + count.ToString();
                
                int quantity = Convert.ToInt32(txt.Text);
                string sql_insert = string.Format("insert into OrderDetails(OrderId,ItemId,Quantity)values('{0}','{1}','{2}')", orderid, itemid, quantity);
                obj.Do_Transaction(sql_insert);
                ScriptManager.RegisterStartupScript(this, this.GetType(), "key", "alert(' Order done Successfully')", true);
            }