C# 2.0学习之事件2

//Copyright (C) Microsoft Corporation.  All rights reserved.

// events2.cs
using System;
namespace MyCollections
{
   using System.Collections;

   // A class that works just like ArrayList, but sends event
   // notifications whenever the list changes:
   public class ListWithChangedEvent: ArrayList
   {
      // An event that clients can use to be notified whenever the
      // elements of the list change:
      public event EventHandler Changed;

      // Invoke the Changed event; called whenever list changes:
      protected virtual void OnChanged(EventArgs e)
      {
         if (Changed != null)
            Changed(this,e);
      }

      // Override some of the methods that can change the list;
      // invoke event after each:
      public override int Add(object value)
      {
         int i = base.Add(value);
         OnChanged(EventArgs.Empty);
         return i;
      }

      public override void Clear()
      {
         base.Clear();
         OnChanged(EventArgs.Empty);
      }

      public override object this[int index]
      {
         set
         {
            base[index] = value;
            OnChanged(EventArgs.Empty);
         }
      }
   }
}

namespace TestEvents
{
   using MyCollections;

   class EventListener
   {
      private ListWithChangedEvent List;

      public EventListener(ListWithChangedEvent list)
      {
         List = list;
         // Add "ListChanged" to the Changed event on "List":
         List.Changed += new EventHandler(ListChanged);
      }

      // This will be called whenever the list changes:
      private void ListChanged(object sender, EventArgs e)
      {
         Console.WriteLine("This is called when the event fires.");
      }

      public void Detach()
      {
         // Detach the event and delete the list:
         List.Changed -= new EventHandler(ListChanged);
         List = null;
      }
   }

   class Test
   {
      // Test the ListWithChangedEvent class:
      public static void Main()
      {
      // Create a new list:
      ListWithChangedEvent list = new ListWithChangedEvent();

      // Create a class that listens to the list's change event:
      EventListener listener = new EventListener(list);

      // Add and remove items from the list:
      list.Add("item 1");
      list.Clear();
      listener.Detach();
      }
   }
}

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csc events2.cs
events2