Assuming you have Remote Desktop or some other access to a server, the system event log is a good place to store information about your application. I personally prefer to put some information into the database, but errors such as the inability to make a database connection obviously would preclude you from storing an error in the database.

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The code to write entries to the event log is fairly straightforward and can easily be added to a base page class or other utility class for ease of use. To configure how the event log writer works, you also can use the configuration file and either a custom configuration section or the standard AppSettings area.

The following code creates three public functions and a private one to do the real work. You easily can read the code to determine which type of entry is being created:

public void LogInformation(string message)
{
   LogEntry(message, EventLogEntryType.Information);
}

public void LogWarning(string message)
{
   LogEntry(message, EventLogEntryType.Warning);
}

public void LogError(string message)
{
   LogEntry(message, EventLogEntryType.Error);
}

private void LogEntry(string message, EventLogEntryType logType)
{
   if (!EventLog.SourceExists("NCS.Web"))
      EventLog.CreateEventSource("NCS.Web", "Application");

   EventLog ncsLog = new EventLog();
   ncsLog.Source = "NCS.Web";
   ncsLog.WriteEntry(message, logType);

}

Each call to LogEntry passes a EventLogEntryType constant, which can be one of the three shown or SuccessAudit or FailureAudit. Inside the LogEntry routine, the code first determines whether an event source called NCS.Web (the internal name for the application) has been created. If it hasn't, it creates the event source with a name and location where the log should be stored—whether it should go to the Application, Security, or System log, or a custom log you can create. In this case, the log entries are placed into the Application log, and then an EventLog object is created, the source is set, and the message is written out. You also can specify an event ID and/or a category for the log entry. This makes it easier to sort through the logs when you are diagnosing a problem.

To make this routine more useful, you also could write the events to a database table or to a flat file because it can be somewhat difficult to view the logs from a Web site.

About the Author

Looking at Windows, Performance Counters, and More

Rating: none

Environment: Visual Basic, C#, .NET

Building great applications isn't all about amazing code snippets that can make your programs look great and run like the wind. It's also about being intelligent—and one big part of that is the ability for your program to look at the world around it (Windows) and figure out exactly what's happening.

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Well, as you can imagine, this is one obviously huge area, so I'll be brief and provide just a few core code tips that'll give you a great starting point when trying to find out just what you want.

First off, to find out about your current environment—such as command line arguments, the user domain name, tick count, and so on—simply explore the System.Environment class. No need for any sticky API calls. Here's a System.Environment example that retrieves the name of the current version of Windows:

x = System.Environment.OSVersion.ToString

To discover more about the actual system itself—such as the computer name, number of monitors attached, whether visual aids should be used rather than audio, the default icon size, and so on—check out the System.Windows.Forms.SystemInformation class. Here's an example that checks whether the computer booted normally (in other words, didn't use safe mode):

                            If
                           System.Windows.Forms.SystemInformation.BootMode = _
  BootMode.Normal 
                            Then
                          
    ' Computer booted in normal mode
End If

Finally, performance counters are an excellent way of tapping into exactly what the system is up to. This is one huge subject on its own and there is already a mound of books written on the subject. However, in brief, performance counters report on the status of the system and its applications. They're predefined and return a number, which you can look at in a variety of formats (an instantaneous figure, an average, percentage, and so forth).

Examples include the amount of system memory available, a processor's busy time, the number of ASP.NET applications running—or even how many SQL Server connections you have open.

You can browse the existing performance monitors by using the Server Explorer (View > Server Explorer), expanding upon your server and exploring the Performance Counters node. If you see an item you think you'll want to use in your code, you can drag it onto your form and manipulate the newly created PerformanceCounter object in code, or just do it all in code. The following snippet demonstrates the latter, displaying the amount of available memory in a message box:

                            Dim
                           perfFreeMemory 
                            As New
                           PerformanceCounter("Memory", _
  "Available MBytes")
MessageBox.Show("There are " & perfFreeMemory.NextValue & _
  "MB of memory available on your system. This program requires _
   more.")

There are a bundle of .NET-specific performance counters available, too—and good system administrators will be more than familiar with these figures, which you can analyse through the PerfMon.exe tool. The .NET revolution also allows you to set up your own custom performance counters with ease, recording data such as the number of sales per second. You can learn more about all of this by looking up "performance counters" in the Help Index, then browsing the subcategories.

Top Tip: If you're attempting to use performance monitors in ASP.NET applications, you may initially find yourself experiencing a bundle of "Access denied" error messages. That's because .NET is picky about exactly who can and can't see this system information. You can resolve this by following the security guidelines at http://aspnet.4guysfromrolla.com/articles/041002-1.aspx. Or, if you're simply wanting to retrieve data such as how long your Web server has been up, check out the tips in Chapter Three of my new book, The Ultimate VB .NET and ASP.NET Code Book.

Figure: Viewing the available Performance Counters through the Server Explorer

About the Author