Display Popup message before session expiry time and Extend Session if they want to extend in asp.net C#

Write below java script function in .aspx page if u are not using master page..other wise write this function Master page .aspx page

<script language=JavaScript>

    var secondsPassed = 0;
    var minutesBeforeLoggedOut = 0;
    var minutesToWarning = 0;

    function ShowTimePassed() {

        minutesBeforeLoggedOut = parseInt(minutesBeforeLoggedOut);
        secondsPassed += 1;

        if (minutesBeforeLoggedOut == -1) {
            if (secondsPassed == 30) {
                var img = new Image(1, 1);
                img.src = 'KeepAlive.aspx?date=' + escape(new Date());
                secondsPassed = 0;
            }
        }
        else {
            if (secondsPassed == minutesToWarning * 60) {
                var answer;

                var currentTime = new Date();
                var expiredTime = new Date();
                var minutes = expiredTime.getMinutes();
                minutes += minutesBeforeLoggedOut;
                expiredTime.setMinutes(minutes);

                if (minutesBeforeLoggedOut == 1) {

                    answer = confirm("It is now " + currentTime.toLocaleTimeString() + " You have " + minutesBeforeLoggedOut + " minute left before getting logged out. Do you want to extend the session?");

                }
                else {

                    answer = confirm("It is now " + currentTime.toLocaleTimeString() + " You have " + minutesBeforeLoggedOut + " minutes left before getting logged out. Do you want to extend the session?");


                } if (answer) {
                    var img = new Image(1, 1);
                    img.src = 'KeepAlive.aspx?date=' + escape(new Date());
                    secondsPassed = 0;
                    currentTime = new Date();
                    if (currentTime > expiredTime) {
                        alert("You've exceeded the time needed to extend the session. You will be logged out now");
                        window.location = loginUrl;
                    }
                }
            }
        }
    }

    window.setInterval('ShowTimePassed()', 1000);
 

</script>

write below two function is .aspx.cs file

  private void keepAlive()
    {

        //figure out the full url of the logout page configured in web.config + the return url which is the current page

        String logoutUrl = FormsAuthentication.LoginUrl + "?ReturnUrl=" + Request.Url;

         String minutesToWarning = "";
        //figure out how many minutes before time out the user wants to get warned.

        String minutesBeforeLoggedOut = "1";
        if (minutesBeforeLoggedOut == null || minutesBeforeLoggedOut == "")
        {
            minutesBeforeLoggedOut = "1";
        }

        //if the user selected "-1", then it never gets timedout. If not, figure out, how many minutes after the page loaded, give the user the warning
        if (!minutesBeforeLoggedOut.Equals("-1"))
        {
            int formsTimeout = GetFormsTimeout();
         //   int formsTimeout = Session.Timeout;
            minutesToWarning = Convert.ToString(formsTimeout - Convert.ToInt32(minutesBeforeLoggedOut));
        }

       String script = @"
                  

<script language=JavaScript>

                        var minutesToWarning = " + minutesToWarning + @";
                        var minutesBeforeLoggedOut = " + minutesBeforeLoggedOut + @";
                        var loginUrl  = '" + logoutUrl + @"';
                   

</script>

                    ";

        if (!Page.ClientScript.IsClientScriptBlockRegistered("WarnTimeOut"))
            Page.ClientScript.RegisterClientScriptBlock(typeof(Page), "WarnTimeOut", script);

    }

    private int GetFormsTimeout()
    {
        System.Xml.XmlDocument x = new System.Xml.XmlDocument();
        x.Load(Request.PhysicalApplicationPath + "/web.config");
        System.Xml.XmlNode node = x.SelectSingleNode("/configuration/system.web/authentication/forms");
        int Timeout = int.Parse(node.Attributes["timeout"].Value, System.Globalization.CultureInfo.InvariantCulture.NumberFormat);
        return Timeout;
    }

and call  keepAlive(); function in Page_Load

 protected void Page_Load(object sender, EventArgs e)
    {
             keepAlive();
    }

and in web.config dont forget to add these lines of code

< authentication mode="Forms">
            <forms timeout="20"/>
        </authentication>

           
       

If your project contains more than one folder and more than one master page..do the same procedure for every master page in every folder in your project

Thanks & Regards

Sathish Sirikonda