Question

I’m a newbie to WMI and I need to implement RegistryValueChangeEvent in a C# service.

I need an event handler that gets triggered each time any one of a set of registry values is changed. I want behavior similar to the FileSystemWatcher class’s Changed event, but for registry values.

If there’s some other technique I could use to accomplish the same task, I’d appreciate that as well. My minimum requirement is that it be a better solution than what I have now: polling every 20 seconds and comparing the registry value with the last result.

Please provide example code in your answer. If I can get an example for watching just one registry value, that would be fine.

I need a solution in .Net 2.0

Thanks.

Answer 1

WMI can sometimes be interesting to work with…I think I understand your question, so take a look at the code snippet below and let me know if it’s what you’re looking for.

// --------------------------------------------------------------------------------------------------------------------- 
// <copyright file="Program.cs" company="">
//   
// </copyright>
// <summary>
//   Defines the WmiChangeEventTester type.
// </summary>
// ---------------------------------------------------------------------------------------------------------------------
namespace WmiExample
{
    using System;
    using System.Management;

    /// <summary>
    /// </summary>
    public class WmiChangeEventTester
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="WmiChangeEventTester"/> class.
        /// </summary>
        public WmiChangeEventTester()
        {
            try
            {
                // Your query goes below; "KeyPath" is the key in the registry that you
                // want to monitor for changes. Make sure you escape the \ character.
                WqlEventQuery query = new WqlEventQuery(
                     "SELECT * FROM RegistryValueChangeEvent WHERE " +
                     "Hive = 'HKEY_LOCAL_MACHINE'" +
                     @"AND KeyPath = 'SOFTWARE\\Microsoft\\.NETFramework' AND ValueName='InstallRoot'");

                ManagementEventWatcher watcher = new ManagementEventWatcher(query);
                Console.WriteLine("Waiting for an event...");

                // Set up the delegate that will handle the change event.
                watcher.EventArrived += new EventArrivedEventHandler(HandleEvent);

                // Start listening for events.
                watcher.Start();

                // Do something while waiting for events. In your application,
                // this would just be continuing business as usual.
                System.Threading.Thread.Sleep(100000000);

                // Stop listening for events.
                watcher.Stop();
            }
            catch (ManagementException managementException)
            {
                Console.WriteLine("An error occurred: " + managementException.Message);
            }
        }

        /// <summary>
        /// </summary>
        /// <param name="sender">
        /// The sender.
        /// </param>
        /// <param name="e">
        /// The e.
        /// </param>
        private void HandleEvent(object sender, EventArrivedEventArgs e)
        {
            Console.WriteLine("Received an event.");
            // RegistryKeyChangeEvent occurs here; do something.
        }

        /// <summary>
        /// </summary>
        public static void Main()
        {
            // Just calls the class above to check for events...
            WmiChangeEventTester receiveEvent = new WmiChangeEventTester();
        }
    }
}