c# - Subscription to Windows Event Log?

Question

I'm working on a project that needs to check the Windows Event Log frequently for certain events. I'm wondering - is there a way to create a subscription to the Windows Event Log for certain events?

So, when the event happens (e.g. event id = 00001), I can get a notification in the code?

If this cannot be done, then I will have to keep searching the event log, which is not efficient.

Answer 1

As you're using C#, I think you should use Windows API to subscribe to certain Windows events. You can do it by using either EventLogWatcher or EventLog class. You can find an example of creating a Windows Event Log subscription using EventLog on MSDN.

If you prefer EventLogWatcher, refer to its limited documentation. And here is my example:

public static void subscribe()
{
    EventLogWatcher watcher = null;
    try
    {
        EventLogQuery subscriptionQuery = new EventLogQuery(
            "Security", PathType.LogName, "*[System/EventID=4624]");

        watcher = new EventLogWatcher(subscriptionQuery);

        // Make the watcher listen to the EventRecordWritten
        // events.  When this event happens, the callback method
        // (EventLogEventRead) is called.
        watcher.EventRecordWritten +=
            new EventHandler<EventRecordWrittenEventArgs>(
                EventLogEventRead);

        // Activate the subscription
        watcher.Enabled = true;

        for (int i = 0; i < 5; i++)
        {
            // Wait for events to occur. 
            System.Threading.Thread.Sleep(10000);
        }
    }
    catch (EventLogReadingException e)
    {
        Log("Error reading the log: {0}", e.Message);
    }
    finally
    {
        // Stop listening to events
        watcher.Enabled = false;

        if (watcher != null)
        {
            watcher.Dispose();
        }
    }
    Console.ReadKey();
}

// Callback method that gets executed when an event is
// reported to the subscription.
public static void EventLogEventRead(object obj,
    EventRecordWrittenEventArgs arg)
{
    // Make sure there was no error reading the event.
    if (arg.EventRecord != null)
    {
        //////
        // This section creates a list of XPath reference strings to select
        // the properties that we want to display
        // In this example, we will extract the User, TimeCreated, EventID and EventRecordID
        //////
        // Array of strings containing XPath references
        String[] xPathRefs = new String[9];
        xPathRefs[0] = "Event/System/TimeCreated/@SystemTime";
        xPathRefs[1] = "Event/System/Computer";
        xPathRefs[2] = "Event/EventData/Data[@Name="TargetUserName"]";
        xPathRefs[3] = "Event/EventData/Data[@Name="TargetDomainName"]";
        // Place those strings in an IEnumberable object
        IEnumerable<String> xPathEnum = xPathRefs;
        // Create the property selection context using the XPath reference
        EventLogPropertySelector logPropertyContext = new EventLogPropertySelector(xPathEnum);

        IList<object> logEventProps = ((EventLogRecord)arg.EventRecord).GetPropertyValues(logPropertyContext);
        Log("Time: ", logEventProps[0]);
        Log("Computer: ", logEventProps[1]);
        Log("TargetUserName: ", logEventProps[2]);
        Log("TargetDomainName: ", logEventProps[3]);
        Log("---------------------------------------");

        Log("Description: ", arg.EventRecord.FormatDescription());
    }
    else
    {
        Log("The event instance was null.");
    }
}