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How Do I...Monitor an event log?



Event logging provides a standard, centralized way for you to have your applications record important software and hardware events. Windows supplies a standard user interface for viewing the logs (Event Log). Using the common language runtime's EventLog component, you can easily connect to existing event logs, and receive event notifications when a new entry is written to the log.

This sample illustrates how to monitor an event log for new entries. It is a small console application that can be run from a command prompt. The application takes one command line argument. The argument is the name of the log that you want to monitor.

Try running the sample as follows: 

> LogMonitor.exe Application


Now run the LogWrite.exe sample and write a new entry to the application log. You will see that the LogMonitor is being notified about the new entry being written.

In its simplest form, monitoring an event log involves:
  1. Creating a new instance of an EventLog component and pointing it to a appropriate event log:

    String log; ... EventLog aLog = new EventLog(); aLog.Log = log; Dim log As String ... Dim aLog As New EventLog aLog.Log = log String* log; ... EventLog* aLog = new EventLog(); aLog->Log = log;


  2. Adding an event handler:

    aLog.EntryWritten += new EventLogEventHandler(OnEntryWritten); AddHandler aLog.EntryWritten, AddressOf OnEntryWritten aLog->EntryWritten += new EntryWrittenEventHandler(this, LogMonitor::OnEntryWritten);


  3. Handling the event notification in your event handler:

    public static void OnEntryWritten(Object source, EventLogEvent e) { Console.WriteLine("Written: " + e.Entry.Message); } Sub OnEntryWritten(ByVal source As Object, ByVal e As EventLogEvent) Console.WriteLine("Written: " + e.Entry.Message) End Sub void OnEntryWritten(Object* source, EntryWrittenEventArgs* e) { Console::WriteLine(String::Concat(S"Written: ", e->Entry->Message)); }

Example