事件是委托的特殊形式。特殊在什么地方呢:事件必须多播。多播必须使用+=而不能用=加载。
事件本身是 Observer 模式“推”模型的标准表现形式。第一个参数object Sender是事件的监测对象,用“this ”的话就是触发事件的类,可以使"观察者"访问到触发事件的类的内部成员变量。第二个参数EventArgs是你要推给"观察者"的数据,当然你要用一个继承自EventArgs的类把这些数据封装好。
示例代码如下:
using System;
using System.Collections.Generic;
using System.Text;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
namespace Delegate
{
// 热水器
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public class Heater
{
private int temperature;
public string type = "RealFire 001"; // 添加型号作为演示
public string area = "China Xian"; // 添加产地作为演示
//声明委托
public delegate void BoiledEventHandler(Object sender, BoiledEventArgs e);
public event BoiledEventHandler Boiled; //声明事件
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
// 定义BoiledEventArgs类,传递给Observer所感兴趣的信息
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public class BoiledEventArgs : EventArgs
{
public readonly int temperature;
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public BoiledEventArgs(int temperature)
{
this.temperature = temperature;
}
}
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
// 可以供继承自 Heater 的类重写,以便继承类拒绝其他对象对它的监视
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
protected virtual void OnBoiled(BoiledEventArgs e)
{
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
if (Boiled != null)
{ // 如果有对象注册
Boiled(this, e); // 调用所有注册对象的方法
}
}
// 烧水。
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public void BoilWater()
{
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
for (int i = 0; i <= 100; i++)
{
temperature = i;
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
if (temperature > 95)
{
//建立BoiledEventArgs 对象。
BoiledEventArgs e = new BoiledEventArgs(temperature);
OnBoiled(e); // 调用 OnBolied方法
}
}
}
}
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
// 警报器
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public class Alarm
{
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public void MakeAlert(Object sender, Heater.BoiledEventArgs e)
{
Heater heater = (Heater)sender; //这里是不是很熟悉呢?
//访问 sender 中的公共字段
Console.WriteLine("Alarm:{0} - {1}: ", heater.area, heater.type);
Console.WriteLine("Alarm: 嘀嘀嘀,水已经 {0} 度了:", e.temperature);
Console.WriteLine();
}
}
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
// 显示器
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public class Display
{
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public static void ShowMsg(Object sender, Heater.BoiledEventArgs e)
{ //静态方法
Heater heater = (Heater)sender;
Console.WriteLine("Display:{0} - {1}: ", heater.area, heater.type);
Console.WriteLine("Display:水快烧开了,当前温度:{0}度。", e.temperature);
Console.WriteLine();
}
}
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
class Program
{
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
static void Main()
{
Heater heater = new Heater();
Alarm alarm = new Alarm();
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
heater.Boiled += alarm.MakeAlert; //注册方法
heater.Boiled += (new Alarm()).MakeAlert; //给匿名对象注册方法
heater.Boiled += new Heater.BoiledEventHandler(alarm.MakeAlert); //也可以这么注册
heater.Boiled += Display.ShowMsg; //注册静态方法
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
heater.BoilWater(); //烧水,会自动调用注册过对象的方法
}
}
}
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
输出为:
Alarm:China Xian - RealFire 001:
Alarm: 嘀嘀嘀,水已经 96 度了:
Alarm:China Xian - RealFire 001:
Alarm: 嘀嘀嘀,水已经 96 度了:
Alarm:China Xian - RealFire 001:
Alarm: 嘀嘀嘀,水已经 96 度了:
Display:China Xian - RealFire 001:
Display:水快烧开了,当前温度:96度。
// 省略 ![](https://www.cnblogs.com/Images/dot.gif)
比较
using System;
using System.Collections.Generic;
using System.Text;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
namespace Delegate
{
// 热水器
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public class Heater
{
private int temperature;
public delegate void BoilHandler(int param); //声明委托
public event BoilHandler BoilEvent; //声明事件
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
// 烧水
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public void BoilWater()
{
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
for (int i = 0; i <= 100; i++)
{
temperature = i;
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
if (temperature > 95)
{
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
if (BoilEvent != null)
{ //如果有对象注册
BoilEvent(temperature); //调用所有注册对象的方法
}
}
}
}
}
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
// 警报器
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public class Alarm
{
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public void MakeAlert(int param)
{
Console.WriteLine("Alarm:嘀嘀嘀,水已经 {0} 度了:", param);
}
}
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
// 显示器
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public class Display
{
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public static void ShowMsg(int param)
{ //静态方法
Console.WriteLine("Display:水快烧开了,当前温度:{0}度。", param);
}
}
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
class Program
{
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
static void Main()
{
Heater heater = new Heater();
Alarm alarm = new Alarm();
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
heater.BoilEvent += alarm.MakeAlert; //注册方法
heater.BoilEvent += (new Alarm()).MakeAlert; //给匿名对象注册方法
heater.BoilEvent += Display.ShowMsg; //注册静态方法
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
heater.BoilWater(); //烧水,会自动调用注册过对象的方法
}
}
}
输出为:
Alarm:嘀嘀嘀,水已经 96 度了:
Alarm:嘀嘀嘀,水已经 96 度了:
Display:水快烧开了,当前温度:96度。
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)