Question

我是asp的新手，所以我觉得答案应该很简单，但我无法弄清楚我做错了什么。这是一个非常简单的购物车练习，我正在学习ASP。我创建会话，添加内容，然后在结帐页面上应该能够逐个从购物车中删除项目。如果单击“删除”，则会从列表框中删除该项目，但不会从会话中删除。我知道它会在会话中持续存在，因为如果我点击购物页面的链接，购物页面上的列表框将填充我认为我删除的项目。

我尝试过两种不同的方法，但我不确定它为什么不起作用。

注意：字典键是用于填充列表框的产品的实际名称。值条目是我现在不实际使用的productID＃。购物页面上的列表框正在填充sqlsource中的数据。 SelectedItem.Text =产品名称（显示为什么）和SelectedValue = productID（未使用）。

非常感谢你的帮助

//Default (shopping) page
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            //Create a new collection for the session indexer
            ArrayList cart = (ArrayList)Session["scart"];

            //Need to initialize a new object in case it's null
            if (cart == null)
            {
                cart = new ArrayList();
                Session["scart"] = cart;
            }

            //Show the shopping car listbox if there are items in it and the 
            //user returned from the checkout page
            else pnlItems.Visible = true;
            foreach (DictionaryEntry item in cart)
            {
                lbItems.Items.Add((string)item.Key);
            }
        }
        //Show the shipping cart listbox containing the items the user just added
        if (IsPostBack) pnlItems.Visible = true;
    }
    private void add_to_cart(string item, int value)
    {
        //Method to add the selected item to the collection/session indexer
        ArrayList cart = (ArrayList)Session["scart"];
        cart.Add(new DictionaryEntry(item, value));
    }
    protected void btnAddItem_Click(object sender, EventArgs e)
    {
        //Method to send the selected item to the add_to_cart method
        string item = ddlProducts.SelectedItem.Text;
        lbItems.Items.Add(item);
        int value = int.Parse(ddlProducts.SelectedValue);
        add_to_cart(item, value);
    }
    protected void ddlProducts_SelectedIndexChanged(object sender, EventArgs e)
    {

    }

    protected void btnCheckOut_Click(object sender, EventArgs e)
    {
        //Send the user to the checkout page when the button is clicked
        Response.Redirect("checkout.aspx", true);
    }

}

//CheckoutPage:
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            //Populate the shopping cart on the checkout page with the items in the collection
            ArrayList cart = (ArrayList)Session["scart"];
            foreach (DictionaryEntry item in cart)
            {
                lbCheckOut.Items.Add((string)item.Key);
            }
        }
    }
    protected void btnKillOrder_Click(object sender, EventArgs e)
    {
        //Kills the order by ending the session, then returns the user to the shopping page.
        Session.Clear();
        Response.Redirect("Default.aspx", true);
    }
    protected void btnRemove_Click(object sender, EventArgs e)
    {
        //Removes the selected item from the shopping cart listbox and the session indexer
        ArrayList cart = (ArrayList)Session["scart"];
        cart.Remove(lbCheckOut.SelectedItem.Text);
        lbCheckOut.Items.Remove(lbCheckOut.SelectedItem.Text);
        Session["scart"] = cart;
        //Session.Remove(lbCheckOut.SelectedItem.Text);
    }
}

Answer 1

您确实在会话状态中添加了DictionaryEntry个实例：

private void add_to_cart(string item, int value)
{
    ArrayList cart = (ArrayList)Session["scart"];
    cart.Add(new DictionaryEntry(item, value));
}

但是你之后试图删除字符串，这不起作用：

protected void btnRemove_Click(object sender, EventArgs e)
{
    ArrayList cart = (ArrayList)Session["scart"];
    cart.Remove(lbCheckOut.SelectedItem.Text);  // Never matches anything.
}

您应该查找键入字符串的DictionaryEntry并删除该条目：

protected void btnRemove_Click(object sender, EventArgs e)
{
    ArrayList cart = (ArrayList) Session["scart"];
    foreach (DictionaryEntry item in cart) {
        if ((string) item.Key == lbCheckOut.SelectedItem.Text) {
            cart.Remove(item);
            break;
        }
    }
}

Answer 2

问题是您的Session对象包含DictionaryEntry实例的ArrayList。因此，cart.Remove(lbCheckOut.SelectedItem.Text)正在尝试将文本与DictionaryEntry实例进行比较，并且每次都返回false。如果你把一个真正的Dictionary实例放在Session而不是ArrayList中会更简单：

if (cart == null)
{
    cart = new Dictionary<string,int>();
    Session["scart"] = cart;
}
...

var cart = (Dictionary<string,int>)Session["scart"];
cart.Remove( lbCheckOut.SelectedItem.Text );

从会话索引（ASP）中删除字典条目

2 个答案: