Client applications can subscribe to receive events from an event-providing application by providing a query that describes the events and establishing a subscription through ManagementEventWatcher.

The client application can wait for an event by calling the System.Management.ManagementEventWatcher.WaitForNextEvent method, which establishes a synchronous subscription to receive events. Alternatively, the client may set up an asynchronous subscription and carry on other operations while waiting for events. For more information, see How To: Receive Management Events Without Waiting.

You create event queries with the EventQuery or WqlEventQuery classes. Both synchronous and asynchronous approaches produce temporary WMI event consumers. A temporary consumer does not resume running after a computer is restarted. For information on creating a permanent consumer, see "Receiving Events at All Times" in the Windows Management Instrumentation documentation in the MSDN Library at http://msdn.microsoft.com/library.

For information on the underlying WMI event structure and available event classes, see "Receiving a WMI Event" in the Windows Management Instrumentation documentation in the MSDN Library at http://msdn.microsoft.com/library. The use of WQL in WMI queries is described in "Querying with WQL" in the Windows Management Instrumentation documentation in the MSDN Library at http://msdn.microsoft.com/library. The syntax reference for WQL is in "WQL (SQL for WMI)" in the Windows Management Instrumentation documentation in the MSDN Library at http://msdn.microsoft.com/library.

Applications that provide events can use System.Management.Instrumentation namespace attribute classes to designate their event classes or derive a new event class from BaseEvent. For more information, see Providing Management Events.

To subscribe to events synchronously

Example

using System;
using System.Management;

// This example shows synchronous consumption of events. 
// The client is blocked while waiting for events. 

public class EventWatcherPolling 
{
    public static int Main(string[] args) 
    {
        // Create event query to be notified within 1 second of 
        // a new process being created
        WqlEventQuery query = 
            new WqlEventQuery("__InstanceCreationEvent", 
            new TimeSpan(0,0,1), 
            "TargetInstance isa \"Win32_Process\"");

        // Initialize an event watcher and subscribe to events 
        // that match this query
        ManagementEventWatcher watcher =
            new ManagementEventWatcher(query);
        // times out watcher.WaitForNextEvent in 5 seconds
        watcher.Options.Timeout = new TimeSpan(0,0,5);
      
        // Block until the next event occurs 
        // Note: this can be done in a loop if waiting for 
        //        more than one occurrence
        Console.WriteLine(
          "Open an application (notepad.exe) to trigger an event.");
        ManagementBaseObject e = watcher.WaitForNextEvent();

        //Display information from the event
        Console.WriteLine(
            "Process {0} has been created, path is: {1}", 
            ((ManagementBaseObject)e
                ["TargetInstance"])["Name"],
            ((ManagementBaseObject)e
                ["TargetInstance"])["ExecutablePath"]);

        //Cancel the subscription
        watcher.Stop();
        return 0;
    }
}

Compiling the Code

See Also