Question

我有一个ASP.NET / VB应用程序我需要选中复选框列表中的选定项目，但复选框是动态来自代码

<asp:Panel ID="panel1" runat="server">
    <asp:Button ID="Button1" runat="server" Text="Save" />
    <asp:Label ID="lbl_Selected_Items" runat="server" Text=""></asp:Label>
</asp:Panel>

代码背后页面加载

Dim CheckBoxList As New CheckBoxList
            pagerview.Controls.Add(CheckBoxList)
            ...est

Button1点击事件

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim CheckBoxList1 As CheckBoxList = CType(Me.FindControl("CheckBoxList"), CheckBoxList)
Dim sCheckedValue As String = ""
For Each oItem As ListItem In CheckBoxList1.Items
    If oItem.Selected Then
        If sCheckedValue = "" Then
            sCheckedValue = ("Selected Value : " + oItem.Value & " Selected Text: ") + oItem.Text
        Else
            sCheckedValue += ("<br/>Selected Value : " + oItem.Value & " Selected Text: ") + oItem.Text
        End If
    End If
Next
lbl_Selected_Items.Text = sCheckedValue

错误文本：null引用异常对象引用未设置为对象的实例 - Error

Answer 1

那发生了什么？错误？没结果？

此时我唯一可以推荐的是在页面init中加载动态控件而不是页面加载。

修改

当您调试时，您会发现按钮单击的第一行上的复选框是Nothing。你的代码中有两个错误。

将控件添加到表单时，不提供id值。而且你没有查找这个值
在按钮中查找控件时，单击FindControl仅查找单个容器。它不是递归的。你应该调用pagerView.FindControl

页面加载（我仍然建议使用init）：

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
Handles Me.Load
    Dim CheckBoxList As New CheckBoxList
    CheckBoxList.ID = "cbl1"
    pagerview.Controls.Add(CheckBoxList)
End Sub

点击按钮：

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim CheckBoxList1 As CheckBoxList = CType(pagerview.FindControl("cbl1"), CheckBoxList)
    Dim sCheckedValue As String = ""
    For Each oItem As ListItem In CheckBoxList1.Items
        If oItem.Selected Then
            If sCheckedValue = "" Then
                sCheckedValue = ("Selected Value : " + oItem.Value & " Selected Text: ") + oItem.Text
            Else
                sCheckedValue += ("<br/>Selected Value : " + oItem.Value & " Selected Text: ") + oItem.Text
            End If
        End If
    Next
    lbl_Selected_Items.Text = sCheckedValue
End Sub

MS Reference

如何检查复选框列表中的选定项目（从代码生成）

1 个答案: