【求助】在GridView1怎么全选复选框

[local]1[/local]是不是这个样子 我想删除我的购物车中的物品，我就选择复选框，然后点击删除商品按钮，次按钮的单击事件代码如下：  protected void btnDelete_Click1(object sender, EventArgs e)
        {
            CheckBox ck = new CheckBox();
            string id = "";
            List<int> listId = new List<int>();
            //取出当前session中用户购物车中的记录
            List<Goods_Order_Item> shopCart = Session["shopCart"] as List<Goods_Order_Item>;
            List<Goods_Order_Item> delShopCart = new List<Goods_Order_Item>();
            //获得用户将要删除的记录id
            foreach (GridViewRow row in this.gvCart.Rows)
            {
                ck = (CheckBox)row.Cells[0].Controls[1];
                if (ck.Checked)
                {
                    id = row.Cells[1].Text;
                    listId.Add(int.Parse(id));
                }
            }

            //遍历用户将要删除的记录id集合,查询出要删除的对象
            foreach (int i in listId)
            {
                foreach (Goods_Order_Item item in shopCart)
                {
                    if (item.GoodsId == i)
                    {
                        delShopCart.Add(item);
                        break;
                    }
                }

            }
            //执行删除
            foreach (Goods_Order_Item item in delShopCart)
            {
                shopCart.Remove(item);
            }
            //从新保存
            Session["shopCart"] = shopCart;
            //从新绑定
            this.gvCart.DataSource = shopCart;
            this.gvCart.DataBind();
        }