如何从后台代码引用动态生成ID的Div？空引用异常求助

问题场景 #

我在尝试引用一个包含动态ID的Div时，始终触发空引用异常，divElement始终返回Nothing。该Div嵌套在gvRenewals GridView控件中，ID通过<%# Eval("Agreement") %>动态生成，相关代码如下：

<div id="div<%# Eval("Agreement") %>" class="childGrid" style="display:none;position:relative;left:25px;">
    <asp:GridView ID="gvHistoricalRenewals" OnRowCommand="gvHistoricalRenewals_RowCommand"
        OnRowDataBound="gvHistoricalRenewals_RowDataBound" runat="server" AutoGenerateColumns="false"
        DataKeyNames="BatchNum" EmptyDataText="No agreements found" Width="80%" CellPadding="4"
        ForeColor="#333333" GridLines="Both">
            <HeaderStyle BackColor="Maroon" Font-Bold="true" ForeColor="White" />
            <RowStyle BackColor="#F7F6F3" ForeColor="#333333" />
            <Columns>
                <asp:ButtonField DataTextField="Agreement" CommandName="Agreement" HeaderText="Agreement" SortExpression="Agreement" meta:resourceKey="lblAgreement" ControlStyle-ForeColor="#822402" />
                <asp:BoundField DataField="CoverageDate" DataFormatString="{0:dd/MM/yyyy}" HeaderText="Coverage Date" SortExpression="CoverageDate" meta:resourceKey="lblCoverageDate" ReadOnly="true" />
                <asp:BoundField DataField="ExpirationDate" DataFormatString="{0:dd/MM/yyyy}" HeaderText="Expiration Date" SortExpression="ExpirationDate" meta:resourceKey="lblExpirationDate" ReadOnly="true" />
                <asp:BoundField DataField="AccountName" HeaderText="Name" SortExpression="AccountName" ReadOnly="true" />
                <asp:BoundField DataField="Location" HeaderText="Location" SortExpression="Location" meta:resourceKey="lblLocation" ReadOnly="true" />
                <asp:BoundField DataField="BillTo" HeaderText="Bill To" SortExpression="BillTo" meta:resourceKey="lblBillTo" ReadOnly="true" />
                <asp:ButtonField CommandName="ShowEquipment" HeaderText="Equipment" Text="Show" ControlStyle-ForeColor="#822402" />
                <asp:BoundField DataField="BatchNum" SortExpression="BatchNum" Visible="false" />
            </Columns>
    </asp:GridView>
</div>

我尝试了两种引用方式，均未成功：

第一种写法：

Dim divElement As HtmlGenericControl = CType(gvRenewals.FindControl("div" & agreement), HtmlGenericControl)

第二种写法：

Dim divElement As HtmlGenericControl = CType(gvRenewals.FindControl("div" & "<%=" & agreement.ToString & "%>"), HtmlGenericControl)

问题原因与解决方法 #

1. 核心问题：控件层级查找错误

gvRenewals作为GridView控件，其直接子控件是每一行的GridViewRow，而非Div。直接调用gvRenewals.FindControl只会查找GridView根节点的直接子控件，无法定位到某一行内部的Div。

2. 正确的查找逻辑

• 先定位Div所在的目标GridViewRow（即gvRenewals中的某一行）
• 在目标行内调用FindControl查找动态ID的Div

3. 具体实现示例

假设你是在gvRenewals的事件（如RowCommand、RowDataBound）中操作，或通过按钮获取对应行：

' 示例：通过CommandArgument获取目标行索引
Dim rowIndex As Integer = Convert.ToInt32(e.CommandArgument)
Dim targetRow As GridViewRow = gvRenewals.Rows(rowIndex)

' 在目标行内查找Div
Dim divElement As HtmlGenericControl = CType(targetRow.FindControl("div" & agreement), HtmlGenericControl)

' 空引用检查
If divElement IsNot Nothing Then
    ' 执行操作，例如切换显示状态
    divElement.Style("display") = "block"
End If

4. 额外注意事项

• 确保agreement变量的值与Eval("Agreement")生成的内容完全一致（注意大小写、空格、特殊字符）
• 若Div在TemplateField模板列中，必须在对应的GridViewRow内查找，而非GridView根节点
• 后端代码无需添加前端渲染语法<%= %>，直接拼接动态ID字符串即可

内容的提问来源于stack exchange，提问作者WhiteGlint