Demonstrates using the Microsoft.SystemEvents class to intercept an event generated by the system


   

/*
C# Programming Tips & Techniques
by Charles Wright, Kris Jamsa

Publisher: Osborne/McGraw-Hill (December 28, 2001)
ISBN: 0072193794
*/

//
// Event.cs -- Demonstrates using the Microsoft.SystemEvents class to intercept
//             an event generated by the system.
//
//             Compile this program with the following command line:
//                 C:>csc Event.cs
//
namespace nsEvent
{
    using System;
    using System.Windows.Forms;
    using Microsoft.Win32;
    
    public class Event
    {
    //
    // Define the delegate
        public delegate void UserEventHandler (object obj, UserPreferenceChangedEventArgs args);
    //
    // Declare a variable that will hold the delegate
        static public event UserEventHandler ShowEvent;
        static public void Main ()
        {
    //
    // Create the delegate using the event handler (below)
              ShowEvent = new UserEventHandler (EvHandler);
    //
    // Creeate the event handler using the new operator
              UserPreferenceChangedEventHandler handler = new UserPreferenceChangedEventHandler(ShowEvent);
    //
    // Add the delegate to the system delegate list. This is a multi-cast delegate
    // and you must use the += operator to add the delegate. Use the -= operator
    // to remove the delegate
              SystemEvents.UserPreferenceChanged += handler;
    //
    // Show a message box to keep the program alive while you cause an event
              MessageBox.Show ("Hey! C Sharp", "System Events");
    //
    // Remove the delegate from the system delegate list
              SystemEvents.UserPreferenceChanged -= handler;
        }
    //
    // Declare and define the method that will be used as the event handler function
        static void EvHandler (object obj, UserPreferenceChangedEventArgs args)
        {
            /* Retrieve the category of the change */

            UserPreferenceCategory cat = args.Category;
            
            /* Build a string for the message box */

            string str = "User changed the " + cat.ToString() + " category";
            /*  Show the change event */
            MessageBox.Show (str, " event category");
        }
    }
}