另一種event的寫法 Ex: EventHandler<DinosaursChangedEventArgs>-优快云博客

本文介绍了一个自定义的恐龙字符串集合类，该类扩展了.NET Framework中的`Collection<T>`泛型集合类，并实现了自定义事件通知机制。每当集合发生添加、删除、替换或清空操作时，都会触发`Changed`事件，通过`DinosaursChangedEventArgs`参数传递具体的变化类型及变化项。

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另一種event的寫法 Ex: EventHandler<DinosaursChangedEventArgs>

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;

public class Dinosaurs : Collection < string >
{
     public event EventHandler < DinosaursChangedEventArgs > Changed;

     protected override void InsertItem( int index, string newItem)
    {
         base .InsertItem(index, newItem);

        EventHandler < DinosaursChangedEventArgs > temp = Changed;
         if (temp != null )
        {
            temp( this , new DinosaursChangedEventArgs(
                ChangeType.Added, newItem, null ));
        }
    }

     protected override void SetItem( int index, string newItem)
    {
         string replaced = Items[index];
         base .SetItem(index, newItem);

        EventHandler < DinosaursChangedEventArgs > temp = Changed;
         if (temp != null )
        {
            temp( this , new DinosaursChangedEventArgs(
                ChangeType.Replaced, replaced, newItem));
        }
    }

     protected override void RemoveItem( int index)
    {
         string removedItem = Items[index];
         base .RemoveItem(index);

        EventHandler < DinosaursChangedEventArgs > temp = Changed;
         if (temp != null )
        {
            temp( this , new DinosaursChangedEventArgs(
                ChangeType.Removed, removedItem, null ));
        }
    }

     protected override void ClearItems()
    {
         base .ClearItems();

        EventHandler < DinosaursChangedEventArgs > temp = Changed;
         if (temp != null )
        {
            temp( this , new DinosaursChangedEventArgs(
                ChangeType.Cleared, null , null ));
        }
    }
}

// Event argument for the Changed event.
//
public class DinosaursChangedEventArgs : EventArgs
{
     public readonly string ChangedItem;
     public readonly ChangeType ChangeType;
     public readonly string ReplacedWith;

     public DinosaursChangedEventArgs(ChangeType change, string item,
         string replacement)
    {
        ChangeType = change;
        ChangedItem = item;
        ReplacedWith = replacement;
    }
}

public enum ChangeType
{
    Added,
    Removed,
    Replaced,
    Cleared
};

public class Demo
{
     public static void Main()
    {
        Dinosaurs dinosaurs = new Dinosaurs();

        dinosaurs.Changed += ChangedHandler;

        dinosaurs.Add( " Psitticosaurus " );
        dinosaurs.Add( " Caudipteryx " );
        dinosaurs.Add( " Compsognathus " );
        dinosaurs.Add( " Muttaburrasaurus " );

        Display(dinosaurs);

        Console.WriteLine( " \nIndexOf(\ " Muttaburrasaurus\ " ): {0} " ,
            dinosaurs.IndexOf( " Muttaburrasaurus " ));

        Console.WriteLine( " \nContains(\ " Caudipteryx\ " ): {0} " ,
            dinosaurs.Contains( " Caudipteryx " ));

        Console.WriteLine( " \nInsert(2, \ " Nanotyrannus\ " ) " );
        dinosaurs.Insert( 2 , " Nanotyrannus " );

        Console.WriteLine( " \ndinosaurs[2]: {0} " , dinosaurs[ 2 ]);

        Console.WriteLine( " \ndinosaurs[2] = \ " Microraptor\ "" );
        dinosaurs[ 2 ] = " Microraptor " ;

        Console.WriteLine( " \nRemove(\ " Microraptor\ " ) " );
        dinosaurs.Remove( " Microraptor " );

        Console.WriteLine( " \nRemoveAt(0) " );
        dinosaurs.RemoveAt( 0 );

        Display(dinosaurs);
    }

     private static void Display(Collection < string > cs)
    {
        Console.WriteLine();
         foreach ( string item in cs)
        {
            Console.WriteLine(item);
        }
    }

     private static void ChangedHandler( object source,
        DinosaursChangedEventArgs e)
    {

         if (e.ChangeType == ChangeType.Replaced)
        {
            Console.WriteLine( " {0} was replaced with {1} " , e.ChangedItem,
                e.ReplacedWith);
        }
         else if (e.ChangeType == ChangeType.Cleared)
        {
            Console.WriteLine( " The dinosaur list was cleared. " );
        }
         else
        {
            Console.WriteLine( " {0} was {1}. " , e.ChangedItem, e.ChangeType);
        }
    }
}