Event关键字

Event关键字

上一篇文章讲的用多播实现订阅者模式。
但是这样还是有些问题。
如果我直接调用了thermostat.OnTemperatureChanged(20)，那么不管温度有没有变化，都会触发所有thermostat订阅者的一个通知。这是因为委托不充分。应该禁止其他类调用OnTemperatureChanged委托。可以通过event关键字解决这个问题。

using  System;
using  System.Collections.Generic;
using  System.Text;
using  System.IO;
using  System.Xml;
using  System.Text.RegularExpressions;


namespace  Happy
{
     class  Cooler
    {
         private   int  _Temperature;

         public  Cooler( int  Temperature)
        {
            _Temperature = Temperature;
        }

         public   int  Temperature
        {
             get
            {
                 return  _Temperature;
            }
             set
            {
                _Temperature = value;
            }
        }

         public   void  OnTemperatureChanged( object  sender,Thermostate.TemperatureArgs NewTemperature)
        {
             if  (NewTemperature.Temperature  <  _Temperature)
            {
                Console.WriteLine( " Cooler On " );
            }
             else  
            {
                Console.WriteLine( " Cooler Off " );
            }
        }
    }

     class  Heater
    {
         private   int  _Temperature;

         public  Heater( int  Temperature)
        {
            _Temperature  =  Temperature;
        }

         public   int  Temperature
        {
             get
            {
                 return  _Temperature;
            }
             set
            {
                _Temperature  =  value;
            }
        }

         public   void  OnTemperatureChanged( object  sender, Thermostate.TemperatureArgs NewTemperature)
        {
             if  (NewTemperature.Temperature  >  _Temperature)
            {
                Console.WriteLine( " Heater On " );
            }
             else
            {
                Console.WriteLine( " Heater Off " );
            }
        }
    }

     public   class  Thermostate
    {
         public   class  TemperatureArgs : EventArgs
        {
             public  TemperatureArgs( int  NewTemperature)
            {
                _Temperature  =  NewTemperature;
            }

             public   int  Temperature
            {
                 get  {  return  _Temperature; }
                 set  { _Temperature  =  value; }
            }
             private   int  _Temperature;
        }

         public   delegate   void  TemperatureChangedHandle( object  sender,TemperatureArgs NewTemperature);
         public   event  TemperatureChangedHandle OnTemperatureChanged;

         private   int  _Temperature;

         public   int  Temperature
        {
             get  {  return  _Temperature; }
             set  
            {
                 if  (value  !=  _Temperature)
                {
                    _Temperature  =  value;
                    TemperatureChangedHandle tmpOnTemperatureChanged  =  OnTemperatureChanged;
                     if  (tmpOnTemperatureChanged  !=   null )
                    {
                        tmpOnTemperatureChanged( this , new  TemperatureArgs(_Temperature));
                    }
                }
            }
        }
    }

     class  Program
    {        
         static   void  Main( string [] args)
        {
            Thermostate thermostat  =   new  Thermostate();

            Cooler cooler  =   new  Cooler( 60 );
            Heater heater  =   new  Heater( 80 );

             string  Temperature;

            thermostat.OnTemperatureChanged  +=  cooler.OnTemperatureChanged;
            thermostat.OnTemperatureChanged  +=  heater.OnTemperatureChanged;

            Temperature  =  Console.ReadLine();

            thermostat.Temperature  =  Convert.ToInt32(Temperature);
        }        
    }
}

这样，用event定义的OnTemperatureChanged就只能出现在+=或者-=得左边了。

并且这样还可以通过sender参数判断是哪个publisher触发了事件。假如heater订阅了两个Thermostat实例，就可以通过sender判断是哪个实例触发了事件