Question

我正在尝试获取一个字符串数组（从上一页的列表框中填充并通过Session传递）并将其显示在标签中，这就是我获取数组的方式：

    Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles CheckOut.Click
    Dim x = ListBox1.GetSelectedIndices.Count
    Dim ListPNames(x) As String
    Dim i As Integer

    i = 0
    For Each item As String In ListBox1.GetSelectedIndices
        ListPNames(i) = (ListBox1.SelectedItem).ToString
        i = i + 1

    Next


    Session("SlctdPhones") = ListPNames(x)

    Response.Redirect("CheckOut.aspx")


End Sub

这就是我试图展示它的方式：

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load


    Dim SlctdPhones() As String = CType(Session.Item("SlctdPhones"), Array)
    Dim i As Integer

    Label3.Text = ""

    For i = 0 To SlctdPhones.Length - 1

    Label3.Text += SlctdPhones(i).ToString() + Environment.NewLine
    Next


End Sub

它给了我一个错误：对象引用未设置为对象的实例。当它到达SlctdPhones.Length - 1行!! 我不知道如何修复它，也是我的数组代码正确（一切都正确存储在其中？）

Answer 1

您声明For循环如下：

For Each item In ...

但是从来没有在循环体中使用item变量。相反，您继续使用相同的SelectedItem属性。您想要将整个方法更改为：

Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles CheckOut.Click
    Dim PNames As New List(Of String)()
    For Each index As Integer In ListBox1.GetSelectedIndices
        PNames.Add(ListBox1.Items(index).Value)
    Next
    Session("SlctdPhones") = PNames

    Response.Redirect("CheckOut.aspx")
End Sub

修复后，Page_Load可以执行此操作：

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    Dim SlctdPhones As List(Of String) = TryCast(Session.Item("SlctdPhones"), List(Of String))

    If SlctdPhones Is Nothing OrElse SlctdPhones.Length = 0 Then
        'Something went wrong here!
        Return
    End If

    Label3.Text = String.Join("<br/>", SlctdPhones.ToArray())
End Sub

但我真的很高兴看到你使用数据控件而不是将<br/>填入标签。这是ListView的标记：

<asp:ListView ID="ListView1" runat="server">
    <LayoutTemplate>
    <ul>
        <asp:PlaceHolder ID="itemPlaceholder" runat="server" />    
    </ul>                
    </LayoutTemplate>
    <ItemTemplate>
    <li><%# Container.DataItem.ToString() %></li>
    </ItemTemplate>
    <EmptyDataTemplate>
    <p>Nothing here.</p>
    </EmptyDataTemplate>
</asp:ListView>

然后Page_Load更简单：

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    ListView1.DataSource =  Session.Item("SlctdPhones")
    ListView1.DataBind()
End Sub

Answer 2

在显示页面上，使用Literal而不是Label

Dim SlctdPhones() As String = CType(Session.Item("SlctdPhones"), Array)
Dim result as String = string.Join("<br>", SlctdPhones) 'Instead of <br> try Environment.NewLine as well 
YourLitetal = result

希望这有帮助！

通过会话将传递的数组写入Label不起作用

2 个答案: