c#学习心得(3)

事件与委托 

 代码段创建类的对象并在该对象上调用方法，此情况下，调用程序是主动，而对象是被动的；但是也有相反的情况，如对象执行过程中发生某些事情通知调用程序，此类事情称之为事件（Event）,z其他代码段编写一种方法接收和处理发布的事件，此过程称之为委托（delegate）。

需要注意的是事件类型与委托标识符要匹配

using System;
/*
public delegate void EvenNumberHandler(int Number);//定义了一个委托

class Counter
{
    public event EvenNumberHandler OnEvenNumber;

    public Counter()
    {
        OnEvenNumber = null;
    }
    public void CountTo100()
    {
        int CurrentNumber;

        for (CurrentNumber = 0; CurrentNumber <= 100; CurrentNumber++)
        { 
        if (CurrentNumber % 2 == 0)
            if (OnEvenNumber != null)

            {
                OnEvenNumber(CurrentNumber);
            }
        }
    }
}
class EvenNumberHandlerClass  
{
    public void EvenNumberFound(int EvenNumber)
    {
        Console.WriteLine(EvenNumber);
    }
}
class EvenNumberHandlerClass2
{
    public void EvenNumberFound2(int EvenNumber1)
    {
        Console.WriteLine(EvenNumber1);
    }
}
class MainClass
{
    public static void Main()
    {
        Counter MyCounter = new Counter();
        EvenNumberHandlerClass MyEvenNumberHandlerClass = new EvenNumberHandlerClass();
        EvenNumberHandlerClass2 MyEvenNumberHandlerClass2 = new EvenNumberHandlerClass2();
       

        MyCounter.OnEvenNumber += new EvenNumberHandler(MyEvenNumberHandlerClass.EvenNumberFound);//可以将任意多的委托
        MyCounter.OnEvenNumber += new EvenNumberHandler(MyEvenNumberHandlerClass2.EvenNumberFound2);  //安装事件，事件在前 委托在后                                                                                     //实例与一个事件联系起来
        MyCounter.CountTo100();
        
    }
}
*/
//标准化事件的设计
public delegate void EvenNumberHandler (object Originator,OnEvenNumberEventArgs EvenNumberEventArgs);

class Counter
{
    public event EvenNumberHandler OnEvenNumber;
    public Counter()
    {
        OnEvenNumber = null;
    }

    public void CountTo100()
    {
        int CurrentNumber;

        for (CurrentNumber = 0; CurrentNumber <= 100; CurrentNumber++)
        {
            if (CurrentNumber % 2 == 0)
            {
                if (OnEvenNumber != null)
                {
                    OnEvenNumberEventArgs EventArguments;

                    EventArguments = new OnEvenNumberEventArgs(CurrentNumber);
                    OnEvenNumber(this, EventArguments);//????存在疑问this到底是如何使用的
                }
            }
        }
    }
}
public class OnEvenNumberEventArgs : EventArgs
{
    private int EvenNumber;

    public OnEvenNumberEventArgs(int EvenNumber)
    {
        this.EvenNumber = EvenNumber;//this
    }

    public int Number
    {
        get
        {
            return EvenNumber;
        }

    }
}
class EventNumberHandlerClass
{
    public void EvenNumberFound(object Originator, OnEvenNumberEventArgs EvenNumberEventArgs)
    {
        Console.WriteLine(EvenNumberEventArgs.Number);
    }
}
class MainClass
{
    public static void Main()
    { 
          Counter  MyCounter = new Counter ();
          EventNumberHandlerClass MyEventNumberHandlerClass = new EventNumberHandlerClass();
          MyCounter.OnEvenNumber += new EvenNumberHandler(MyEventNumberHandlerClass.EvenNumberFound);
          MyCounter.CountTo100();
   
    }

}