引发和使用事件(引用自MSDN)

下面的示例程序阐释如何在一个类中引发一个事件，然后在另一个类中处理该事件。AlarmClock 类定义公共事件 Alarm，并提供引发该事件的方法。AlarmEventArgs 类派生自 EventArgs，并定义 Alarm 事件特定的数据。WakeMeUp 类定义处理 Alarm 事件的 AlarmRang 方法。AlarmDriver 类一起使用类，将使用 WakeMeUp 的 AlarmRang 方法设置为处理 AlarmClock 的 Alarm 事件。

该示例程序使用事件和委托和引发事件中详细说明的概念。

c# 代码

// EventSample.cs.
//
namespace EventSample
{
   using System;
   using System.ComponentModel;

   // Class that contains the data for
   // the alarm event. Derives from System.EventArgs.
   //
   public class AlarmEventArgs : EventArgs
   {
      private readonly bool snoozePressed ;
      private readonly int nrings;

      //Constructor.
      //
      public AlarmEventArgs(bool snoozePressed, int nrings)
      {
         this.snoozePressed = snoozePressed;
         this.nrings = nrings;
      }

      // The NumRings property returns the number of rings
      // that the alarm clock has sounded when the alarm event
      // is generated.
      //
      public int NumRings
      {
         get { return nrings;}
      }

      // The SnoozePressed property indicates whether the snooze
      // button is pressed on the alarm when the alarm event is generated.
      //
      public bool SnoozePressed
      {
         get {return snoozePressed;}
      }

      // The AlarmText property that contains the wake-up message.
      //
      public string AlarmText
      {
         get
         {
            if (snoozePressed)
            {
               return ("Wake Up!!! Snooze time is over.");
            }
            else
            {
               return ("Wake Up!");
            }
         }
      }
   }

   // Delegate declaration.
   //
   public delegate void AlarmEventHandler(object sender, AlarmEventArgs e);

   // The Alarm class that raises the alarm event.
   //
   public class AlarmClock
   {
      private bool snoozePressed = false;
      private int nrings = 0;
      private bool stop = false;

      // The Stop property indicates whether the
      // alarm should be turned off.
      //
      public bool Stop
      {
         get {return stop;}
         set {stop = value;}
      }

      // The SnoozePressed property indicates whether the snooze
      // button is pressed on the alarm when the alarm event is generated.
      //
      public bool SnoozePressed
      {
         get {return snoozePressed;}
         set {snoozePressed = value;}
      }
      // The event member that is of type AlarmEventHandler.
      //
      public event AlarmEventHandler Alarm;

      // The protected OnAlarm method raises the event by invoking
      // the delegates. The sender is always this, the current instance
      // of the class.
      //
      protected virtual void OnAlarm(AlarmEventArgs e)
      {
        AlarmEventHandler handler = Alarm;
        if (handler != null)
        {
           // Invokes the delegates.
           handler(this, e);
        }
      }

      // This alarm clock does not have
      // a user interface.
      // To simulate the alarm mechanism it has a loop
      // that raises the alarm event at every iteration
      // with a time delay of 300 milliseconds,
      // if snooze is not pressed. If snooze is pressed,
      // the time delay is 1000 milliseconds.
      //
      public void Start()
      {
         for (;;)
         {
            nrings++;
            if (stop)
            {
               break;
            }

            else if (snoozePressed)
            {
               System.Threading.Thread.Sleep(1000);
               {
                  AlarmEventArgs e = new AlarmEventArgs(snoozePressed,
                     nrings);
                  OnAlarm(e);
               }
            }
            else
            {
               System.Threading.Thread.Sleep(300);
               AlarmEventArgs e = new AlarmEventArgs(snoozePressed,
                  nrings);
               OnAlarm(e);
            }
         }
      }
   }

   // The WakeMeUp class has a method AlarmRang that handles the
   // alarm event.
   //
   public class WakeMeUp
   {

      public void AlarmRang(object sender, AlarmEventArgs e)
      {

         Console.WriteLine(e.AlarmText +"\n");

         if (!(e.SnoozePressed))
         {
            if (e.NumRings % 10 == 0)
            {
               Console.WriteLine(" Let alarm ring? Enter Y");
               Console.WriteLine(" Press Snooze? Enter N");
               Console.WriteLine(" Stop Alarm? Enter Q");
               String input = Console.ReadLine();

               if (input.Equals("Y") ||input.Equals("y")) return;

               else if (input.Equals("N") || input.Equals("n"))
               {
                  ((AlarmClock)sender).SnoozePressed = true;
                  return;
               }
               else
               {
                  ((AlarmClock)sender).Stop = true;
                  return;
               }
            }
         }
         else
         {
            Console.WriteLine(" Let alarm ring? Enter Y");
            Console.WriteLine(" Stop Alarm? Enter Q");
            String input = Console.ReadLine();
            if (input.Equals("Y") || input.Equals("y")) return;
            else
            {
               ((AlarmClock)sender).Stop = true;
               return;
            }
         }
      }
   }


   // The driver class that hooks up the event handling method of
   // WakeMeUp to the alarm event of an Alarm object using a delegate.
   // In a forms-based application, the driver class is the
   // form.
   //
   public class AlarmDriver
   {
      public static void Main (string[] args)
      {
         // Instantiates the event receiver.
         WakeMeUp w= new WakeMeUp();

         // Instantiates the event source.
         AlarmClock clock = new AlarmClock();

         // Wires the AlarmRang method to the Alarm event.
         clock.Alarm += new AlarmEventHandler(w.AlarmRang);

         clock.Start();
      }
   }
}

地址：http://msdn2.microsoft.com/zh-cn/library/9aackb16(VS.80).aspx

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• 2007-03-19 13:15
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