为什么我不能单击ListView中的ImageButton？

Question

我想在我的asp.net应用程序中使用listview控件，并在itemtemplate图像按钮中使用。我想如果我点击这个按钮，我可以使div块可见= true，并用listview行中的数据填充控件。

我的列表视图：

 <asp:ListView runat="server" ID="myListView" OnItemCommand="myListView_ItemCommand"
            OnSelectedIndexChanging="myListView_SelectedIndexChanging">

                <LayoutTemplate>

                    <table id="UserList" border="1" cellpadding="0" cellspacing="0">
                        <tr style="background-color:#ccdaeb">
                            <th>
                               <span class="spanpading"><asp:Label ID="lblNameHeader" runat="server" Text="_Name"></asp:Label></span> </th>
                                <th>
                                  <span class="spanpading"><asp:Label ID="lblCompanyHeader" runat="server" Text="_Firma"></asp:Label></span></th>
                                    <th >
                                       <span class="spanpading"><asp:Label ID="lblVonHeader" runat="server" Text="_gültig ab"></asp:Label></span></th>
                                        <th >
                                            <span class="spanpading"><asp:Label ID="lblBisHeader" runat="server" Text="_gültig bis"></asp:Label></span></th>
                                            <th >
                                               <span class="spanpading"><asp:Label ID="lblErstellerHeader" runat="server" Text="_erstellt von"></asp:Label></span> </th>
                            <th align="left">
                                </th>
                            <th align="left">
                                </th>
                            <th align="left">
                              </th>
                        </tr>
                        <tr id="itemPlaceholder" runat="server"></tr>
                    </table>

                </LayoutTemplate>

                <ItemTemplate>
                    <tr onmouseover="this.style.backgroundColor='#87CEFA'"
                    onmouseout="this.style.backgroundColor='#ffffff'">
                        <td align="left"><span class="spanpading"><asp:Label ID="lblname" Text='<%# Eval("NAME") %>' runat="server"  /></span></td>
                        <td align="left"><span class="spanpading"><asp:Label ID="lblcompany" Text='<%# Eval("COMPANY") %>' runat="server"  /></span></td>
                        <td align="left"><span class="spanpading"><asp:Label ID="lblVon" Text='<%# Eval("TIMEFROM") %>' runat="server"  /></span></td>
                        <td align="left"><span class="spanpading"><asp:Label ID="lblBis" Text='<%# Eval("TIMETO") %>' runat="server"  /></span></td>
                        <td align="left"><span class="spanpading"><asp:Label ID="lblErsteller" Text='<%# Eval("CREATOR") %>' runat="server"  /></span></td>
                        <td align="left"><asp:ImageButton ID="imgDelete" runat="server" ToolTip="löschen" ImageUrl="images/delete.gif" /></td>
                        <td align="left"><asp:ImageButton ID="imgUpdate" runat="server" ToolTip="ändern" ImageUrl="images/edit.gif" CommandName="update" CommandArgument='<%# Container.DataItemIndex %>' /></td>
                        <td align="left"><asp:ImageButton ID="imgEmail" runat="server" ToolTip="Zugangsdaten senden" ImageUrl="images/send.gif" /></td>

                    </tr>
                </ItemTemplate>

                <EmptyDataTemplate>
                    <h4>Es wurden keine Einträge gefunden</h4><br/>

                </EmptyDataTemplate>

                <AlternatingItemTemplate>
                    <tr style="background-color: #E5EDF5;" onmouseover="this.style.backgroundColor='#87CEFA'"
                    onmouseout="this.style.backgroundColor='#E5EDF5'">
                        <td align="left"><span class="spanpading"><asp:Label ID="lblname" Text='<%# Eval("NAME") %>' runat="server"  /></span></td>
                        <td align="left"><span class="spanpading"><asp:Label ID="lblcompany" Text='<%# Eval("COMPANY") %>' runat="server"  /></span></td>
                        <td align="left"><span class="spanpading"><asp:Label ID="lblVon" Text='<%# Eval("TIMEFROM") %>' runat="server"  /></span></td>
                        <td align="left"><span class="spanpading"><asp:Label ID="lblBis" Text='<%# Eval("TIMETO") %>' runat="server"  /></span></td>
                        <td align="left"><span class="spanpading"><asp:Label ID="lblErsteller" Text='<%# Eval("CREATOR") %>' runat="server"  /></span></td>
                        <td align="left"><asp:ImageButton ID="imgDelete" runat="server" ToolTip="löschen" ImageUrl="images/delete.gif" /></td>
                        <td align="left"><asp:ImageButton ID="imgUpdate" runat="server" ToolTip="ändern" ImageUrl="images/edit.gif" CommandName="update" CommandArgument='<%# Container.DataItemIndex %>' /></td>
                        <td align="left"><asp:ImageButton ID="imgEmail" runat="server" ToolTip="Zugangsdaten senden" ImageUrl="images/send.gif" /></td>
                    </tr>
                </AlternatingItemTemplate>

            </asp:ListView>

这是m＆lt; commandItem的代码：

 protected void myListView_SelectedIndexChanging(object sender, EventArgs e)
        {
            //
        }

        protected void myListView_ItemCommand(object sender, ListViewCommandEventArgs e)
        {
            if (e.CommandName == "update")
            {
                int index = Convert.ToInt32(e.CommandArgument);

                Label lbName = (Label)myListView.Items[index].FindControl("lblname");
                Label lbFirma = (Label)myListView.Items[index].FindControl("lblcompany");
                Label lbVon = (Label)myListView.Items[index].FindControl("lblVon");
                Label lbBis = (Label)myListView.Items[index].FindControl("lblBis");

                //Übergabe an die Div Update Box

                draggablebox.Visible = true; 
            }
        }

这是错误消息：