Question

我有一个将项目添加到我的arraylist的功能。我的问题是它每次只保留一个项目，因为每次单击我的按钮时它都会重新初始化阵列。如果尚未创建数组，VB中的语法只是初始化？

 Dim itemSelectAs New ArrayList()
 Dim Quantities As New ArrayList()
 Dim itemQtyOrdered As Integer

Public Sub ShtickDataList_ItemCommand(ByVal source As Object, ByVal e As System.Web.UI.WebControls.ListViewCommandEventArgs) Handles ShtickDataList.ItemCommand


    If e.CommandName = "addToCart" Then
        Dim itemQuantity As DropDownList = e.Item.FindControl("QuantityDropDown")
        itemQtyOrdered = itemQuantity.SelectedValue
        ItemSelect.Add(e.CommandArgument)
        Quantities.Add(itemQtyOrdered)

        Session("itemInCart") = ItemSelect
        Session("quantities") = Quantities


        viewInvoice()

    End If


End Sub

Protected Sub viewInvoice()

    Dim itemSelected As ArrayList = DirectCast(Session("itemInCart"), ArrayList)
    Dim QuantityofItem As ArrayList = DirectCast(Session("quantities"), ArrayList)

    Dim conn As SqlConnection
    Dim comm As SqlCommand
    Dim reader As SqlDataReader
    Dim purimConnection2 As String = ConfigurationManager.ConnectionStrings("Purim").ConnectionString
    conn = New SqlConnection(purimConnection2)

    comm = New SqlCommand("SELECT ProductName FROM Products WHERE ProductID = @ProductID", conn)

    Dim i As Integer
    For i = 0 To ItemSelect.Count - 1
    comm.Parameters.Add("@ProductID", Data.SqlDbType.Int)
    comm.Parameters("@ProductID").Value = (ItemSelected.Count - 1)

    'Next

    Try
        conn.Open()
        reader = comm.ExecuteReader()
        ViewCartlink.Text = "View Cart: (" & ItemSelected.Count & ")"



    Finally
        conn.Close()
    End Try
End Sub

Answer 1

首先，您需要确定数组列表的尺寸。

 Dim array_list as ArrayList()

然后你可以实例化一个

 array_list = new ArrayList

或者您可以将其合并为一步：

 Dim array_list = new ArrayList()

之后，您可以使用

添加和删除数组列表中的元素

 array_list.add(obj)

并删除

 array_list.remove(obj)

看起来你的问题与访问arraylist的成员有关。新项目总是添加到arraylist的末尾。要直接访问它们，您需要它们的索引。如果您知道要访问的项目的索引，请使用

 array_list(i)

如果不这样做，则需要遍历数组。要做到这一点，你有两个选择。您可以使用“for each”或者您可以使用普通for循环并使用array_list.count作为上限。

每次调用按钮单击菜单时，都会重新创建两个会话值。您需要将它们从Session变量中拉出来并将它们放在局部变量中并将它们放回到会话变量中。

您的按钮方法应为：

 Public Sub ShtickDataList_ItemCommand(ByVal source As Object, ByVal e As System.Web.UI.WebControls.ListViewCommandEventArgs) Handles ShtickDataList.ItemCommand


   if isNothing(itemSelect) Then itemSelect = New ArrayList()
   if isNothing(itemQtyOrdered) Then itemQtyOrdered= New ArrayList()

   If e.CommandName = "addToCart" Then


       Dim itemQuantity As DropDownList = e.Item.FindControl("QuantityDropDown")
       itemQtyOrdered = itemQuantity.SelectedValue
       ItemSelect.Add(e.CommandArgument)
       Quantities.Add(itemQtyOrdered)

       Session("itemInCart") = ItemSelect
       Session("quantities") = Quantities


       viewInvoice()

   End If


 End Sub

将全局通话更改为：

 Dim itemSelect As ArrayList() = Session("itemInCart")
 Dim Quantities As New ArrayList() = Session("quantities")

Answer 2

在按钮单击事件之外定义数组。（表格级别）

然后在按钮点击事件中尝试：

If myArrayList Is Nothing then
   'initializes the array list only if that hasn't happened yet
   myArrayList = new ArrayList
End If
'adds the item to the existing list without causing it to reintialize
myArrayList.add(item)

如果它没有被初始化，那么它就会被初始化，但如果它已经存在则被初始化。如果它在表单级别初始化，即...已声明为new，那么您可以添加它。

基本上确保你没有在按钮点击事件中为arrayList调用New。

编辑网络表单：

您应该检查初始化arrayList的位置。就像在Page_Load：

中一样

If Not Page.IsPostBack Then
  myArrayList = New ArrayList
End If

MSDN Postback

我如何初始化我的arraylist

2 个答案: