最简单的 ajax Loading 效果

<asp:UpdatePanel ID="UpdatePanel2" runat="server">
          <ContentTemplate>
        <asp:GridView ID="GvPubList" runat="server" AutoGenerateColumns="False"
                CellPadding="4" ForeColor="#333333" GridLines="None"
                Width="100%" AllowPaging="True"
                OnPageIndexChanging="GvPubList_PageIndexChanging">
                <PagerSettings FirstPageText="首页" LastPageText="尾页" Position="Bottom"
                    Mode="NumericFirstLast" NextPageText="下一页" PreviousPageText="上一页"
                    PageButtonCount="5" />
                .............            </asp:GridView>
            </ContentTemplate>
            </asp:UpdatePanel>
<asp:UpdateProgress ID="UpdateProgress2" runat="server" AssociatedUpdatePanelID="UpdatePanel2">  
             <ProgressTemplate>  
                 <img alt="loading" src="images/ajax-loader.gif" />
         &n