CS/WebSite/Default.aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<%@ Register Assembly="DevExpress.Web.v13.1, Version=13.1.14.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a"
    Namespace="DevExpress.Web" 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">

    <script type="text/javascript">
        function OnBtnShowPopupClick() {
            popup.Show();
        }
        function HidePopupAndShowInfo(closedBy, returnValue) {
            popup.Hide();
            alert('Closed By: ' + closedBy + '\nReturn Value: ' + returnValue);
        }
    </script>

    <title></title>
</head>
<body>
    <form id="form1" runat="server">
        <div>
            <input id="btnShowPopup" type="button" onclick="OnBtnShowPopupClick();" value="Show Popup" />
            <dx:ASPxPopupControl ID="popup" runat="server" ClientInstanceName="popup" ContentUrl="~/PopupContent.aspx"
                Width="300px" Height="200px">
            </dx:ASPxPopupControl>
            
        </div>
    </form>
</body>
</html>