ASP.NET Display "Loading..." message while update panel is updating

You can use code as below when

using Image as Loading

<asp:UpdateProgress id="updateProgress" runat="server">    <ProgressTemplate>        <div style="position: fixed; text-align: center; height: 100%; width: 100%; top: 0; right: 0; left: 0; z-index: 9999999; background-color: #000000; opacity: 0.7;">            <asp:Image ID="imgUpdateProgress" runat="server" ImageUrl="~/images/ajax-loader.gif" AlternateText="Loading ..." ToolTip="Loading ..." style="padding: 10px;position:fixed;top:45%;left:50%;" />        </div>    </ProgressTemplate></asp:UpdateProgress>

using Text as Loading

<asp:UpdateProgress id="updateProgress" runat="server">    <ProgressTemplate>        <div style="position: fixed; text-align: center; height: 100%; width: 100%; top: 0; right: 0; left: 0; z-index: 9999999; background-color: #000000; opacity: 0.7;">            <span style="border-width: 0px; position: fixed; padding: 50px; background-color: #FFFFFF; font-size: 36px; left: 40%; top: 40%;">Loading ...</span>        </div>    </ProgressTemplate></asp:UpdateProgress>

Awesome tutorial: 3 Different Ways to Display Progress in an ASP.NET AJAX Application

You can use the UpdateProgress control:

Also see:ajax "loading" icon with UpdatePanel postbacks