Question

我遇到了这个动态创建控件的代码。我尝试过这个。但是，每当我运行它时，对象引用未设置为对象错误的实例弹出并指向代码中的某一行（我把---＆gt;放在行上）。我是这种编程语言的新手。我不知道该怎么做。

这是我得到的代码：

Imports System.Collections.Generic
'Imports System.Data.Odbc

Partial Public Class main
Inherits System.Web.UI.Page
Private controlCounter As Integer = 0
Private myControlList As List(Of String)

Protected Overrides Sub LoadViewState(ByVal savedState As Object)
    MyBase.LoadViewState(savedState)
    myControlList = DirectCast(ViewState("myControlList"), List(Of String))
    For Each ctlID As String In myControlList
        controlCounter += 1
        Dim hyper As New HyperLink()
        hyper.ID = ctlID
        Dim lineBreak As New LiteralControl("<br />")
        PlaceHolder1.Controls.Add(hyper)
        PlaceHolder1.Controls.Add(lineBreak)
    Next
End Sub

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
    If Not IsPostBack Then
        myControlList = New List(Of String)()
        ViewState("myControlList") = myControlList
    End If
End Sub


Protected Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button1.Click
    controlCounter += 1
    Dim hyper As New HyperLink()
    hyper.Text = "a new text Box"
    hyper.ID = "hyperlink" + controlCounter.ToString()
    Dim lineBreak As New LiteralControl("<br />")
    PlaceHolder1.Controls.Add(hyper)
    PlaceHolder1.Controls.Add(lineBreak)
  -->      myControlList.Add(hyper.ID)
    ViewState("myControlList") = myControlList

End Sub
End Class

请帮帮我。感谢。

Answer 1

单击按钮会启动回发，如果请求不回发，您只需将myControlList设置为某个内容，所以没有任何内容。

如果你想在页面加载时创建列表，然后只是继续添加它，那么你需要在创建后将myControlList推送到Session或其他内容中它，然后在按钮上再次单击检索它，添加到它，并在会话中重新设置它。

要执行此操作，请添加和获取会话内容，执行，

Session("someDistinctKey") = myControlList;
myControlList = CType(Session("someDisctintKey"), List(Of String))

分别

对象引用未设置为ASP中的对象实例（vb）

1 个答案: