<%@ Page Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true" CodeFile="Example.aspx.cs"
    Inherits="ASPxLoadingPanel_Example" %>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentHolder" runat="Server">
    <dx:ASPxCallback ID="ASPxCallback1" runat="server" ClientInstanceName="Callback">
        <ClientSideEvents CallbackComplete="function(s, e) { LoadingPanel.Hide(); }" />
    </dx:ASPxCallback>
    <div class="BottomPadding">
        <dx:ASPxCheckBox ID="ASPxCheckBox1" runat="server" AutoPostBack="true" Checked="True"
            Text="Display the ASPxLoadingPanel over a specific control">
        </dx:ASPxCheckBox>
    </div>
    <table id="Panel" style="border: Dashed 1px Gray; height: 125px; width: 60%; margin: 30px 20%">
        <tr>
            <td align="center" valign="middle">
                <dx:ASPxButton ID="ASPxButton1" runat="server" Text="Show Loading Panel" AutoPostBack="False">
                    <ClientSideEvents Click="function(s, e) {
    Callback.PerformCallback();
    LoadingPanel.Show();
}" />
                </dx:ASPxButton>
            </td>
        </tr>
    </table>
    <dx:ASPxLoadingPanel ID="LoadingPanel" runat="server" ClientInstanceName="LoadingPanel"
        Modal="True">
    </dx:ASPxLoadingPanel>
</asp:Content>
C#
using System;
using System.Threading;
using System.Web.UI;

public partial class ASPxLoadingPanel_Example : Page {

    protected void Page_Load(object sender, EventArgs e) {
        if(IsCallback) {
            // Intentionally pauses server-side processing,
            // to demonstrate the Loading Panel functionality.
            Thread.Sleep(500);
        }
        LoadingPanel.ContainerElementID = ASPxCheckBox1.Checked ? "Panel" : "";
    }

}

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>

<%@ Register Assembly="DevExpress.Web.ASPxEditors.v10.2, Version=10.2.10.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a"
    Namespace="DevExpress.Web.ASPxEditors" TagPrefix="dx" %>
<%@ Register Assembly="DevExpress.Web.v10.2, Version=10.2.10.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a"
    Namespace="DevExpress.Web.ASPxTabControl" TagPrefix="dx" %>
<%@ Register Assembly="DevExpress.Web.v10.2, Version=10.2.10.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a"
    Namespace="DevExpress.Web.ASPxClasses" TagPrefix="dx" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:ScriptManager ID="ScriptManager1" runat="server">
        </asp:ScriptManager>
        <%--<asp:UpdatePanel ID="UpdatePanel1" runat="server">
                            <ContentTemplate>--%>
        <dx:ASPxPageControl ID="ASPxPageControl1" runat="server" ActiveTabIndex="0" EnableCallBacks="True"
            CssFilePath="../../styles.css" Height="350px" Width="100%">
            <TabPages>
                <dx:TabPage Text="Main">
                    <ContentCollection>
                        <dx:ContentControl ID="ContentControl1" runat="server">
                            <asp:Panel ID="MainMainTab1" runat="server" Visible="True" Width="100%">
                                <asp:UpdatePanel ID="UpdatePanel1" runat="server">
                                    <ContentTemplate>
                                        <table>
                                            <tr>
                                                <td class="fieldlabel" style="height: 1px" align="right" width="30%">
                                                    Terms&nbsp;
                                                </td>
                                                <td width="70%">
                                                    <dx:ASPxComboBox ID="cbTermsID1" runat="server" DataSourceID="dsTerms" Width="99%"
                                                        DropDownWidth="550px" TextFormatString="{0}" EnableIncrementalFiltering="True"
                                                        CallbackPageSize="10" DropDownStyle="DropDown" ValueType="System.Int32" ValueField="CategoryID"
                                                        TextField="CategoryName" AutoPostBack="True" ClientIDMode="AutoID" IncrementalFilteringMode="StartsWith">
                                                        <Columns>
                                                            <dx:ListBoxColumn FieldName="CategoryID" />
                                                            <dx:ListBoxColumn FieldName="CategoryName" />
                                                        </Columns>
                                                    </dx:ASPxComboBox>
                                                    <asp:SqlDataSource ID="dsTerms" runat="server" ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString %>"
                                                        SelectCommand="SELECT [CategoryID], [CategoryName] FROM [Categories]"></asp:SqlDataSource>
                                                </td>
                                            </tr>
                                        </table>
                                        <asp:UpdateProgress runat="server" ID="UpdateProgress1" AssociatedUpdatePanelID="UpdatePanel1"
                                            DisplayAfter="0" DynamicLayout="false">
                                            <ProgressTemplate>
                                                <div style="position: absolute; z-index: 10; left: expression((this.offsetParent.clientWidth/2)-(this.clientWidth/2)+this.offsetParent.scrollLeft);
                                                    top: expression((this.offsetParent.clientHeight/2)-(this.clientHeight/2)+this.offsetParent.scrollTop);
                                                    background-color: #ffffff; border: 2px solid #908C8C; width: 120px; height: 30px;">
                                                    &nbsp;<img src="../../Images/ajax-loader.gif" />
                                                    <font style="font-size: 8pt" face="arial" color="#716D6D">&nbsp;Please Wait...</font>
                                                </div>
                                            </ProgressTemplate>
                                        </asp:UpdateProgress>
                                    </ContentTemplate>
                                </asp:UpdatePanel>
                            </asp:Panel>
                        </dx:ContentControl>
                    </ContentCollection>
                </dx:TabPage>
                <dx:TabPage Text="Memos">
                    <ContentCollection>
                        <dx:ContentControl ID="ContentControl2" runat="server">
                            <asp:Panel ID="Panel1" runat="server" Visible="True" Width="100%">
                                <asp:UpdatePanel ID="UpdatePanel2" runat="server">
                                    <ContentTemplate>
                                        <table>
                                            <tr>
                                                <td class="fieldlabel" style="height: 1px" align="right" width="30%">
                                                    Price Category Types&nbsp;
                                                </td>
                                                <td width="70%">
                                                    <dx:ASPxComboBox ID="cbPriceCategoryID1" runat="server" Width="100%" DropDownWidth="550"
                                                        TextFormatString="{0}" EnableIncrementalFiltering="True" CallbackPageSize="10"
                                                        DropDownStyle="DropDown" ValueType="System.String" ValueField="PriceCategoryID"
                                                        TextField="PriceCategoryID" AutoPostBack="True">
                                                        <Columns>
                                                            <dx:ListBoxColumn FieldName="PriceCategoryID" />
                                                            <dx:ListBoxColumn FieldName="PriceCategoryDesc" />
                                                        </Columns>
                                                    </dx:ASPxComboBox>
                                                </td>
                                            </tr>
                                        </table>
                                        <asp:UpdateProgress runat="server" ID="UpdateProgress2" AssociatedUpdatePanelID="UpdatePanel2"
                                            DisplayAfter="0" DynamicLayout="false">
                                            <ProgressTemplate>
                                                <div style="position: absolute; z-index: 10; left: expression((this.offsetParent.clientWidth/2)-(this.clientWidth/2)+this.offsetParent.scrollLeft);
                                                    top: expression((this.offsetParent.clientHeight/2)-(this.clientHeight/2)+this.offsetParent.scrollTop);
                                                    background-color: #ffffff; border: 2px solid #908C8C; width: 120px; height: 30px;">
                                                    &nbsp;<img src="../../Images/ajax-loader.gif" />
                                                    <font style="font-size: 8pt" face="arial" color="#716D6D">&nbsp;Please Wait...</font>
                                                </div>
                                            </ProgressTemplate>
                                        </asp:UpdateProgress>
                                    </ContentTemplate>
                                </asp:UpdatePanel>
                            </asp:Panel>
                        </dx:ContentControl>
                    </ContentCollection>
                </dx:TabPage>
            </TabPages>
        </dx:ASPxPageControl>
        <%--<asp:UpdateProgress runat="server" ID="UpdateProgress1" AssociatedUpdatePanelID="UpdatePanel1" DisplayAfter="0" DynamicLayout="false">
                                    <ProgressTemplate>
                                        <div style="position:absolute;z-index:10;left:expression((this.offsetParent.clientWidth/2)-(this.clientWidth/2)+this.offsetParent.scrollLeft);
                                        top:expression((this.offsetParent.clientHeight/2)-(this.clientHeight/2)+this.offsetParent.scrollTop);background-color:#ffffff;border:2px solid #908C8C;width: 120px; height: 30px;">
                                        &nbsp;<img src="../../Images/ajax-loader.gif" /> <FONT style="FONT-SIZE: 8pt" face="arial" color="#716D6D">&nbsp;Please Wait...</FONT>
                                        </div>
                                    </ProgressTemplate>
                                </asp:UpdateProgress>
                            </ContentTemplate>
                        </asp:UpdatePanel>--%>
    </div>
    </form>
</body>
</html>