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Prevent Session Timeout in

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Prevent Session Timeout in [VB]

ASP.Net 2.0 [VB]

Inspired by this article from Code Project. [Thanks Ach1lles ]

I slightly modified few things to work for VB and VS2005 environment. The code works perfect and I’m very happy with it.First I created a Module file and created this function.

Public Function KeepAlive() As String

        Dim int_MilliSecondsTimeOut As Integer = (HttpContext.Current.Session.Timeout * 60000) - 30000
        Dim sScript As New StringBuilder
        sScript.Append("<script type='text/javascript'>" & vbNewLine)
        'Number Of Reconnects
        sScript.Append("var count=0;" & vbNewLine)
        'Maximum reconnects Setting
        sScript.Append("var max = 6;" & vbNewLine)
        sScript.Append("function Reconnect(){" & vbNewLine)
        sScript.Append("count++;" & vbNewLine)
        sScript.Append("var d = new Date();" & vbNewLine)
        sScript.Append("var curr_hour = d.getHours();" & vbNewLine)
        sScript.Append("var curr_min = d.getMinutes();" & vbNewLine)
        sScript.Append("if (count < max){" & vbNewLine)
        sScript.Append("window.status = 'Refreshed ' + count.toString() + ' time(s) &#91;' + curr_hour + ':' + curr_min + '&#93;';" & vbNewLine)
        sScript.Append("var img = new Image(1,1);" & vbNewLine)
        sScript.Append("img.src = 'http://localhost/myapp/reconnect.aspx';" & vbNewLine)

        sScript.Append("}" & vbNewLine)
        sScript.Append("}" & vbNewLine)
        sScript.Append(int_MilliSecondsTimeOut.ToString() & "); //Set to length required" & vbNewLine)

        KeepAlive = sScript.ToString
End Function

All this code does is, build a simple javascript function and its called from server side.The works like this,- Gets the current session timeout duration.
– Subtract 30 seconds from it and assign it to MilliSecondsTimeOut variable
– Create a Reconnect() javascript function
– Create a global variable with max value 6
– Get current hour and Min [just for displaying the last refresh time]
– Verify whether count is less than max value (ie 6)
– If so, change the window status with Text
– Create a dummy image and set reconnect.aspx url as its source [this way a call is made to server and it wont session timeout]Create a timer using window.setInterval and assign the MilliSecondsTimeOut value.
[this way this function is called 30 seconds before session timeout]Tha max value (6) can be set to any number. If its 6 then this session timeout is avoided 5 times.

Default session timeout is 20min. 20 * 5 = 100 mins. Which is good for non-secure page.


On the pages where I want to prevent Session Timeout I entered this line.

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
  'dont forget to add this line 
  Page.ClientScript.RegisterClientScriptBlock(Me.GetType, "reconn key", KeepAlive())
 If Not Page.IsPostBack Then
 End If

Catch eX as Exception
End Try
End Sub

Created reconnect.aspx in Visual Studio and deleted the .vb and .designer.vb files.This is the final version of reconnect.aspx

<%@ Page Language="vb" AutoEventWireup="false"%>
<%@ OutputCache Location="None" VaryByParam="None" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "<a href="" mce_href=""></a>">
<html xmlns="<a href="" mce_href=""></a>" >

Note : When you compile the project sometimes, VS2005 complains reconnect.aspx is not in right format.
So I EXCLUDED this file from my project. Now VS 2005 will compile without complaining and the logic will also work.- Happy Programming

Written by gchandra

November 26, 2007 at 3:42 pm