ex-12-04

Programming Csharp Source Code(代码) Programming Csharp Source Code

// Example 12-04: Working with events

namespace Programming_CSharp
{
   using System;
   using System.Threading;

   // a class to hold the information about the event
   // in this case it will hold only information 
   // available in the clock class, but could hold
   // additional state information 
   public class TimeInfoEventArgs : EventArgs
   {
      public TimeInfoEventArgs(int hour, int minute, int second)
      {
         this.hour = hour;
         this.minute = minute;
         this.second = second;
      }
      public readonly int hour;
      public readonly int minute;
      public readonly int second;
   }

   // our subject -- it is this class that other classes
   // will observe. This class publishes one event: 
   // OnSecondChange. The observers subscribe to that event
   public class Clock
   {
      // the delegate the subscribers must implement
      public delegate void SecondChangeHandler
         (
         object clock, 
         TimeInfoEventArgs timeInformation
         );

      // the event we publish
      public event SecondChangeHandler OnSecondChange;

      // set the clock running
      // it will raise an event for each new second
      public void Run()
      {
         for(;;)
         {
            // sleep 10 milliseconds
            Thread.Sleep(10);
                
            // get the current time
            System.DateTime dt = System.DateTime.Now;

            // if the second has changed
            // notify the subscribers
            if (dt.Second != second)
            {
               // create the TimeInfoEventArgs object
               // to pass to the subscriber
               TimeInfoEventArgs timeInformation = 
                  new TimeInfoEventArgs(
                     dt.Hour,dt.Minute,dt.Second);

               // if anyone has subscribed, notify them
               if (OnSecondChange != null)
               {
                  OnSecondChange(
                     this,timeInformation);
               }
            }

            // update the state
            this.second = dt.Second;
            this.minute = dt.Minute;
            this.hour = dt.Hour;

         }
      }
      private int hour;
      private int minute;
      private int second;
   }

   // an observer. DisplayClock subscribes to the 
   // clock's events. The job of DisplayClock is 
   // to display the current time 
   public class DisplayClock
   {
      // given a clock, subscribe to 
      // its SecondChangeHandler event
      public void Subscribe(Clock theClock)
      {
         theClock.OnSecondChange +=
            new Clock.SecondChangeHandler(TimeHasChanged);
      }

      // the method that implements the 
      // delegated functionality
      public void TimeHasChanged(
         object theClock, TimeInfoEventArgs ti)
      {
         Console.WriteLine("Current Time: {0}:{1}:{2}",
            ti.hour.ToString(), 
            ti.minute.ToString(), 
            ti.second.ToString());
      }
   }

   // a second subscriber whose job is to write to a file
   public class LogCurrentTime
   {
      public void Subscribe(Clock theClock)
      {
         theClock.OnSecondChange +=
            new Clock.SecondChangeHandler(WriteLogEntry);
      }

      // this method should write to a file
      // we write to the console to see the effect
      // this object keeps no state
      public void WriteLogEntry(
         object theClock, TimeInfoEventArgs ti)
      {
         Console.WriteLine("Logging to file: {0}:{1}:{2}",
            ti.hour.ToString(), 
            ti.minute.ToString(), 
            ti.second.ToString());
      }
   }

   public class Test
   {
      public static void Main()
      {
         // create a new clock 
         Clock theClock = new Clock();

         // create the display and tell it to
         // subscribe to the clock just created
         DisplayClock dc = new DisplayClock();
         dc.Subscribe(theClock);

         // create a Log object and tell it
         // to subscribe to the clock 
         LogCurrentTime lct = new LogCurrentTime();
         lct.Subscribe(theClock);

         // Get the clock started
         theClock.Run();
      }
   }
}