Programming Visual Basic .NET

Application-Level Code and global.asax

All of the code shown so far has been written at the page level, appearing either in an .aspx file or in a code-behind file that implements a Page-derived class. However, there needs to be a way to handle events and manipulate properties at the application level as well, without regard to any particular page. For this purpose there is the global.asax file. global.asax is a file that optionally can appear in a web application’s root directory. If it is present, it can contain code and settings that are automatically processed by the ASP.NET framework at the appropriate times.

Session and Application Startup and Shutdown

Some applications may need to run certain code whenever a new session is started or is about to end, or when the application as a whole is first started or is about to end. This is done by placing code in the application’s global.asax file, as shown in Example 6-9.

Example 6-9. Responding to session and application start and end in a global.asax file

<script language="vb" runat="server">
   
   Public Sub Session_OnStart(  )
      ' ...
   End Sub
   
   Public Sub Session_OnEnd(  )
      ' ...
   End Sub

   Public Sub Application_OnStart(  )
      ' ...
   End Sub
   
   Public Sub Application_OnEnd(  )
      ' ...
   End Sub
   
</script>

Notice that code is placed in <script> blocks.

The code in Example 6-9 defines four subroutines:

Session_OnStart

Called by the ASP.NET framework when a session starts

Session_OnEnd

Called by the ASP.NET framework when a session ends

Application_OnStart

Called by ...