C#委托和事件的使用实例

// 热水器
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

// 定义BoiledEventArgs类，传递给Observer所感兴趣的信息
public class BoiledEventArgs : EventArgs
{
public readonly int temperature;
public BoiledEventArgs(int temperature)
{
this.temperature = temperature;
}
}
// 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
protected virtual void OnBoiled(BoiledEventArgs e)
{
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。（第一次调用该方法）
public void BoilWater()
{
for (int i = 0; i <= 100; i++)
{
temperature = i;
if (temperature > 98)
{
//建立BoiledEventArgs 对象。
BoiledEventArgs e = new BoiledEventArgs(temperature);
OnBoiled(e); // 调用 OnBolied方法（触发事件的方法）
}
}
}
}

// 警报器
public class Alarm
{
public void MakeAlert(Object sender, Heater.BoiledEventArgs e)
{
Heater heater = (Heater)sender;
//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();
}
}

// 显示器
public class Display
{
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();
}
}

class Program
{
public static void Main()
{
Heater heater = new Heater();
Alarm alarm = new Alarm();

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

heater.BoilWater(); //烧水，会自动调用注册过对象的方法(按照顺序调用)
}
}