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Question

未将对象引用设置到对象的实例。 
说明: 执行当前 Web 请求期间，出现未处理的异常。请检查堆栈跟踪信息，以了解有关该错误以及代码中导致错误的出处的详细信息。 异常详细信息: System.NullReferenceException: 未将对象引用设置到对象的实例。源错误: 
行 70:             int gridviewQuantity = Convert.ToInt16(GridViewShoppingCartList.DataKeys[i].Value);//int.Parse(GridViewShoppingCartList.Rows[i].Cells[3].Text);
行 71:                 //if textboxquantity is changed and checkedRemove is checked!
行 72:             if( quantity!=gridviewQuantity||checkBoxRemove.Checked==true)
行 73:             {
行 74:                 Label labelBookId = (Label)GridViewShoppingCartList.Rows[i].FindControl("LabelBookId");
 源文件: f:\MyOnNetBookSell\ShoppingCarts.aspx.cs    行: 72以下是代码:    protected void UpdateShoppingCartList()
    {
        ShoppingCart cart = new ShoppingCart();
        //obtain current user's shopping cart id
        string cartId = cart.GetShoppingCartID();
        //itarate through all rows with the shopping cart
        for (int i = 0; i < GridViewShoppingCartList.Rows.Count;i++ )
        {
            //
            TextBox textBoxQuantity = (TextBox)GridViewShoppingCartList.Rows[i].FindControl("TextBoxQuantity");
        
            CheckBox checkBoxRemove = (CheckBox)GridViewShoppingCartList.Rows[i].FindControl("TextBoxRemove");
            int quantity;
            //try
            //{
            quantity = int.Parse(textBoxQuantity.Text);
            int gridviewQuantity = Convert.ToInt16(GridViewShoppingCartList.DataKeys[i].Value);//int.Parse(GridViewShoppingCartList.Rows[i].Cells[3].Text);
                //if textboxquantity is changed and checkedRemove is checked!
            if( quantity!=gridviewQuantity||checkBoxRemove.Checked==true)
            {
                Label labelBookId = (Label)GridViewShoppingCartList.Rows[i].FindControl("LabelBookId");
                if (quantity == 0 || checkBoxRemove.Checked == true)//运行到这里就报上面那个错
                {
                    cart.RemoveItems(cartId,Int32.Parse(labelBookId.Text));
                }
                else
                {
                    cart.UpdateItems(cartId,Int32.Parse(labelBookId.Text),quantity);
                }
            }
            //}
            //catch
           
            //{
            //   LabelError.Visible = true;
            //  LabelError.Text = "There has been a problem with one or more of your inputs.";
            //}        }
   
    }

Answer 1

checkBoxRemove 
没有找到复选框.!

Answer 2

是没有取到值, 取的值为null

Answer 3

Insus.NET改了一下:protected void UpdateShoppingCartList() 
    { 
        ShoppingCart cart = new ShoppingCart(); 
        //obtain current user's shopping cart id 
        string cartId = cart.GetShoppingCartID(); 
        //itarate through all rows with the shopping cart 
        for (int i = 0; i  < GridViewShoppingCartList.Rows.Count;i++ ) 
        {            GridViewRow dvr = GridViewShoppingCartList.Rows[i];  //Insus.NET添加此句            if (dvr.FindControl("TextBoxQuantity") != null && dvr.FindControl("TextBoxRemove") != null)  //Insus.NET更改此句
            {
                TextBox textBoxQuantity = (TextBox)dvr.FindControl("TextBoxQuantity"); //Insus.NET更改此句
                CheckBox checkBoxRemove = (CheckBox)dvr.FindControl("TextBoxRemove");//Insus.NET更改此句
                int quantity;
                //try 
                //{ 
                quantity = int.Parse(textBoxQuantity.Text);
                int gridviewQuantity = Convert.ToInt16(GridViewShoppingCartList.DataKeys[i].Value);//int.Parse(dvr.Cells[3].Text); 
                //if textboxquantity is changed and checkedRemove is checked! 
                if (quantity != gridviewQuantity || checkBoxRemove.Checked == true)
                {
                    Label labelBookId = (Label)dvr.FindControl("LabelBookId");//Insus.NET更改此句                    if (quantity == 0 || checkBoxRemove.Checked)//Insus.NET更改此句
                    {
                        cart.RemoveItems(cartId, Int32.Parse(labelBookId.Text));
                    }
                    else
                    {
                        cart.UpdateItems(cartId, Int32.Parse(labelBookId.Text), quantity);
                    }
                }
                //} 
                //catch                 //{ 
                //   LabelError.Visible = true; 
                //  LabelError.Text = "There has been a problem with one or more of your inputs."; 
                //} 
            }
        }     
    }