GridView RowDeleting 为什么执行了两次

我以前的 购物车的时候 有时候也是这样的点一下 有时候买了一个 有时候买了两个我是放在GridView1_SelectedIndexChanged事件里面的 看到你也有这个问题所以也提出来 程序真的没有问题! void Session_Start(object sender, EventArgs e) 
    {
        // 在新会话启动时运行的代码
        Session["MyShoppingCart"] = new WebShoppingCart();
        //读取当前统计人数
        Application.Lock();
        Application["Count"] = Convert.ToInt32(Application["Count"]) + 1;
        Application.UnLock();
        //写入Count.txt文件中
        StreamWriter sw = new StreamWriter(Server.MapPath("Count.txt"), false);
        sw.WriteLine(Application["Count"]);
        sw.Close();
    }protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
    {
        //创建实例
        WebShoppingCart cart = (WebShoppingCart)Session["MyShoppingCart"];
        try
        {
            string pid = GridView1.SelectedDataKey.Value.ToString();
            if (cart != null)
            {
                cart.DeleteItem(pid);
                Profile.ShoppingCart.DeleteItem(pid);
                Total.Text = String.Format("合计:{0:c}", cart.TotalCost);
                //删除后的绑定,下面可以不要因为Page_Load事件绑定了
                //ShoppingCart cart = (ShoppingCart)Session["MyShoppingCart"];
                //GridView1.DataSource = cart.Orders;
                GridView1.DataBind();
            }
        }
        catch
        {
            //这个是为了判断用户删除了商品
            //但是点击后退按钮后商品还在
            //在点击删除出现得异常,用刷新该页来解决
            Response.Redirect("View_ShoppingCart.aspx");
        }
    }类namespace WendwCart    //命名空间名称
{
    [Serializable]
    public class Stat_Class
    {
        private String ShangPinID; //商品ID
        private String Sp_Name; //商品名称
        private decimal Sp_Price; //商品价格
        private int Sp_Quan; //商品数量        public string ItemID
        {
            get { return ShangPinID; }
            //set { ShangPinID = value; }
        }        public string ShangpinName
        {
            get { return Sp_Name; }
            //set { Sp_Name = value; }
        }        public decimal Price
        {
            get { return Sp_Price; }
            //set { Sp_Price = value; }
        }        public int Quantity
        {
            get { return Sp_Quan; }
            set { Sp_Quan = value; }
        }        //构造方法，初始化商品的各个属性
        public Stat_Class(string ItemID, string ShangpinName, decimal Price, int Quantity)
        {
            ShangPinID = ItemID;
            Sp_Name = ShangpinName;
            Sp_Price = Price;
            Sp_Quan = Quantity;
        }
    }    [Serializable]
    public class WebShoppingCart
    {
        public WebShoppingCart()
        {
            //
            // TODO: 在此处添加构造函数逻辑
            //
        }
        Hashtable Cart_Orders = new Hashtable();
        //该属性返回Hashtable的ICollection集合作数据源
        public ICollection Orders
        {
            get { return Cart_Orders.Values; }
        }        //计算总价格属性
        public decimal TotalCost
        {
       get {
                decimal Total = 0;
                foreach (DictionaryEntry entry in Cart_Orders)
                {
                    Stat_Class order = (Stat_Class)entry.Value;
                    Total += (order.Price * order.Quantity);
                }
                return Total;
            }
        }        //添加物件方法
        public void AddItem(Stat_Class Order)
        {
            Stat_Class order = (Stat_Class)Cart_Orders[Order.ItemID];
            if (order != null)
            {
                order.Quantity += 1;
            }
            else
            {
                Cart_Orders.Add(Order.ItemID, Order);
            }
        }        //删除物件方法
        public void DeleteItem(string ItemID)
        {
            if (Cart_Orders[ItemID] != null)
            {
                Cart_Orders.Remove(ItemID);
            }
        }
    }