C#_delegate - 用委托实现事件，Display和Log类都使用Clock对象

//public event SecondChangeHandler OnSecondChange; 若将委托加上event，则视作是事件，不是委托，外围就不能直接对OnSecondChange传值

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace EventClock
{
//一个存放事件信息的类
//存放这Clock类中的信息，和其他状态信息
public class TimeInfoEventArg : EventArgs
{
public TimeInfoEventArg(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;
}

//中心类：其他类要订阅的类
//发布一个委托
//OnSecondChange
public class Clock
{
private int hour;
private int minute;
private int second;
//订阅这必须实现的委托
public delegate void SecondChangeHandler(object clcok, TimeInfoEventArg timeInformation);
//委托实例
public SecondChangeHandler OnSecondChange;

//设置始终运行，每一秒都触发一个事件
public void Run()
{
for (; ; )
{
//休眠10秒
Thread.Sleep(10);
//获取当前时间
System.DateTime dt = System.DateTime.Now;
//如秒钟改变，通知订阅者
if (dt.Second != second)
{
//创建TimeInfoEventArg对象，传给订阅者
TimeInfoEventArg timeInformation = new TimeInfoEventArg(dt.Hour,dt.Minute,dt.Second);
//如果有订阅者，通知他们
if (OnSecondChange != null)
{
OnSecondChange(this, timeInformation);
}

}
this.second = dt.Second;
this.minute = dt.Minute;
this.hour = dt.Hour;
}
}
}
//一个订阅者，DisplayClock订阅
//时钟事件，DisplayClock任务是显示当前时间
public class DisplayClock
{
//对于给定的时钟，订阅其他OnSecondChange事件
public void Subscribe(Clock theClock)
{
theClock.OnSecondChange += new Clock.SecondChangeHandler(TimeHasChanged);

}

//实现委托功能的方法
public void TimeHasChanged(object clcok, TimeInfoEventArg timeInformation)
{
Console.WriteLine("Current time: {0}:{1}:{2}",
timeInformation.hour.ToString(),
timeInformation.minute.ToString(),
timeInformation.second.ToString());
}
}

//另一个订阅者，其任务写入文件
public class LogCurrentTime
{
public void Subscribe(Clock theClock)
{
theClock.OnSecondChange += new Clock.SecondChangeHandler(WriteLogEntry);
}
//此方法应该写入文件
//写到控制台是为了看到对象不保存状态的效果
public void WriteLogEntry(
object theClcok, TimeInfoEventArg ti)
{
Console.WriteLine("logging to file: {0}:{1}:{2}",
ti.hour.ToString(), ti.minute.ToString(), ti.second.ToString());
}
}

class Program
{
static void Main(string[] args)
{
Clock theClock = new Clock();

//创建时钟对象，订阅刚刚创建的时钟
DisplayClock dc = new DisplayClock();
dc.Subscribe(theClock);
//创建Log对对象
LogCurrentTime lct = new LogCurrentTime();
lct.Subscribe(theClock);

theClock.Run();
Console.ReadLine();
}
}
}

//匿名方法，无需在注册实例委托

public void Subscribe(Clock theClock)
{
theClock.OnSecondChange += delegate(object clcok, TimeInfoEventArg timeInformation)
{
Console.WriteLine("Current time: {0}:{1}:{2}",
timeInformation.hour.ToString(),
timeInformation.minute.ToString(),
timeInformation.second.ToString());
};

}