C# Cookbook

6.10. Watching the Event Log for a Specific Entry

Problem

You may have multiple applications that write to a single event log. For each of these applications, you want a monitoring application to watch for one or more specific log entries to be written to the event log. For example, you might want to watch for a log entry that indicates that an application encountered a critical error or shut down unexpectedly. These log entries should be reported in real time.

Solution

Monitoring an event log for a specific entry requires the following steps:

1. Create the following method to set up the event handler to handle event log writes:

   public void WatchForAppEvent(EventLog log)
   {
       log.EnableRaisingEvents = true;
       log.EntryWritten += new EntryWrittenEventHandler(OnEntryWritten);
   }

2. Create the event handler to examine the log entries and determine whether further action is to be performed. For example:

   public static void OnEntryWritten(object source, 
                                     EntryWrittenEventArgs entryArg) 
   {
       if (entryArg.Entry.EntryType == EventLogEntryType.Error)
       {
           Console.WriteLine(entryArg.Entry.Message);
           Console.WriteLine(entryArg.Entry.Category);
           Console.WriteLine(entryArg.Entry.EntryType.ToString( ));
           // Do further actions here as necessary...
       }
   }

Discussion

This recipe revolves around the EntryWrittenEventHandler delegate, which calls back a method whenever any new entry is written to the event log. The EntryWrittenEventHandler delegate accepts two arguments: a source of type object and an entryArg of type EntryWrittenEventArgs ...