为listview加载gif ItemTemplate

Question

我在listvew中有这个表

<asp:ListView ID="listid" runat="server" GroupPlaceholderID="groupPlaceHolder1"
ItemPlaceholderID="itemPlaceHolder1" OnPagePropertiesChanging="OnPagePropertiesChanging">
<LayoutTemplate>
    <table id="tblid" class="datatable">
        <thead>
            <tr>
                header column
            </tr>
        </thead> 
        <tbody>
        <asp:PlaceHolder runat="server" ID="groupPlaceHolder1"></asp:PlaceHolder>
        </tbody>       
    </table>
</LayoutTemplate>
<GroupTemplate>
    <tr class="trowcount">
        <asp:PlaceHolder runat="server" ID="itemPlaceHolder1"></asp:PlaceHolder>
    </tr>
</GroupTemplate>

<ItemTemplate>
    table columns list
</ItemTemplate>

</asp:ListView>

这个表的查询需要一段时间，所以我想把简单的加载gif 放在这里

<ItemTemplate>
       table columns list
</ItemTemplate>

直到查询完成。

后端就像：

Using cmd As New SqlCommand()
    cmd.CommandText = "my query"
    cmd.Connection = con
    Using sda As New SqlDataAdapter(cmd)
        Dim dt As New DataTable()
        sda.Fill(dt)
        lvExport.DataSource = dt
        lvExport.DataBind()
    End Using
End Using