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One of the more common questions I've found on the net is 'How do you show the number of current users browsing my site?", like ASPNet101.com has on the bottom left of each page. This tutorial will take the mystery out of this by breaking it down, piece by piece.

It all starts with the Global.asax file. For those of you who have come from the Classic ASP world, you will probably recognize the name of this file, since Classic ASP also had a Global.asa file. Here, we track the active Sessions for our application. There are three subroutines into which we'll be looking to do this - Application_OnStart, Session_OnStart, and the Session_OnEnd.

First, in the Application_OnStart sub, we basically set the user count to 0, when the server starts

Sub Application_OnStart (Sender as Object, E as EventArgs)
	' Set our user count to 0 when we start the server 
	Application("ActiveUsers") = 0
End Sub

Next, in the Session_OnStart subroutine, there are several things happening:

Sub Session_OnStart (Sender as Object, E as EventArgs)
	Session.Timeout = 10
	Session("Start") = Now 
	Application.Lock 
		Application("ActiveUsers") = Cint(Application("ActiveUsers")) + 1 
	Application.UnLock
End Sub

The first thing is the Timeout - you don't need to put anything here, but, the default Timeout is 20 minutes, so you can change or add it, depending on the needs of your particular application.

To set the session start time, we add (Session("Start") = Now). Basically, when the user hits the site and opens a web page (asp.net), at the time he/she opens the page, the session starts. Next, we increase the active visitors count when we start the session (Application("ActiveUsers") = Cint(Application("ActiveUsers")) + 1 ). The Application lock & unlock adds more stability to the counting.

Next, we must decrement the number of online sessions in the Session_OnEnd subroutine:

Sub Session_OnEnd(Sender as Object, E as EventArgs)
	Application.Lock 
		Application("ActiveUsers") = Cint(Application("ActiveUsers")) - 1 
	Application.UnLock
End Sub

As you can see, it's pretty much the same code as adding to the current session count - Except - we subtract one from the count, decreasing the active visitors count when the session ends.

The last thing to do is to display the count on the page. In this site, I have a user control that shows up on the left side of every page, which does this. Including it in a user control makes it much easier to maintain, since it only needs to be changed in one place and not on every page. As you can see here, very little code is actually necessary to show the current session/user count:

<% 
Dim intNumber as Integer
intNumber =Application("ActiveUsers")
response.write (intNumber ) 
%> Currently Online

Of course, you can use any html tags you'd like to format this in exactly the way you'd like for your site.

So now, you can see that the tracking and displaying the number of current sessions/users is a very simple process and can be implemented with little or no fuss on your own site.