從會話索引（ASP）中刪除字典條目

Question

我是asp新的品牌，所以我認爲這個答案應該是一個簡單的方法，但我無法弄清楚我做錯了什麼。這是一個非常簡單的購物車練習，我正在學習ASP。我創建了會話，添加了一些內容，然後在結帳頁面上可以逐個刪除購物車中的物品。如果我點擊刪除，該項目將從列表框中刪除，但不會從會話中刪除。我知道它在會話中仍然存在，因爲如果我點擊鏈接到購物頁面，購物頁面上的列表框將填充我認爲已刪除的項目。

我試着去除它兩種不同的方式，我不知道爲什麼它不工作。

注意：字典鍵是用於填充列表框的產品的實際名稱。值條目是我現在沒有實際使用的productID＃。購物頁面上的列表框正在填充來自sqlsource的數據。 SelectedItem.Text =產品名稱（顯示內容）和SelectedValue = productID（未使用）。

非常感謝您的幫助

//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

您確實要添加DictionaryEntry實例會話狀態：

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

但是你要刪除後弦，不能正常工作：

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

您應該查找以DictionaryEntry爲鍵的您的字符串，並刪除該條目，而不是：

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

問題是，您的會話對象包含一個ArrayList的DictionaryEntry實例。因此，cart.Remove(lbCheckOut.SelectedItem.Text)正在嘗試將文本與DictionaryEntry實例進行比較，並且每次都返回false。如果你在Session中放置一個真正的Dictionary實例而不是ArrayList，那會更簡單：

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

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