Visual Basic 1002005 [A Developers Notebook] [Electronic resources] نسخه متنی

4.10. Determine How Many People Are Currently Using Your Web Site

The
Web uses HTTP, a stateless protocol that rarely maintains a
connection longer than a few seconds. As a result, even as users are
reading through your web pages, they aren't
connected directly to your server. However, ASP.NET gives you a way
to estimate how many people are using your web site at any given
moment using timestamps. This information makes
a great addition to a community site (e.g., a web discussion forum),
and it can also be useful for diagnostic purposes.

Note: Ever wondered how many people are using your site
right now? If you're using ASP.
NET's personalization features,
it's remarkably easy to get a reasonable
estimate.

4.10.1. How do I do that?

Every time a user logs in using a membership provider (described in
the lab "Easily Authenticate
Users"), ASP.NET records the current time in the
data store. When the same user requests a new page, ASP.NET updates
the timestamp accordingly. To make a guess at how many people are
using your web site, you can count the number of users who have a
timestamp within a short window of time. For example, you might
consider the number of users who have requested a page in the last 15
minutes.

You can retrieve this information from ASP.NET using the new
GetNumberOfUsersOnline() method of the Membership class. You
can also configure the time window that will be used by setting the
UserIsOnlineTimeWindow property (which reflects a
number of minutes). It's set to 15 by default.

Here's a code snippet that counts the online users
and displays the count in a label:

Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
lblStatus.Text &= "<br>There are " &_
Membership.GetNumberOfUsersOnline( ) & _
" users online right now. That is an estimate based" &_
" on looking at timestamps that fall in the last " &_
Membership.UserIsOnlineTimeWindow & _
" minutes."
End Sub

Keep in mind that this count doesn't include
anonymous users.

4.10.2. What about...

...getting information about exactly which users are online?
Unfortunately, ASP.NET doesn't currently provide any
way to determine which users are online. The only alternative is to
add your own tracking code. For example, you could store this
information in a database or add it to an in-memory object such as
the Application collection whenever a user logs
in. You would also need to store the login time and discard old
entries periodically.