委托的注册及注销+观察者模式

事件

委托变量如果公开出去，很不安全，外部可以随意调用

所以取消public,封闭它，我们可以自己书写两个方法，供外部注册与注销，委托调用在子方法里调用，这样封装委托变量可以使它更安全，这个就叫做事件

1.外部不能随便调用，只能注册和注销

2.只能自己去调用自己的委托

委托练习题：

老师会在下课时打铃（事件）

学生们想在打铃事件发生的时候做自己的事情：

小明想在打铃的时候去买东西吃，

小张想在打铃时去打水，

小红想在打铃时开始练习，

小花想在打铃时去打羽毛球。

代码如下：

using System;namespace 事件
{public delegate void CallDelegate();class Teacher{public string name;CallDelegate callDel;public void RegisterCallEvent(CallDelegate del){callDel += del;}public void LogoutCallEvent(CallDelegate del){callDel -= del;}public Teacher(string name){this.name = name;}public void Call(){Console.WriteLine("{0}打铃了！",name);if (callDel != null){callDel();}}}class Student{public string name;public string action;public Student(string name, string action){this.name = name;this.action = action;}public void DoThing(){Console.WriteLine(name + action);}}class Program{static void Main(string[] args){Teacher teacher = new Teacher("王老师");Student xiaoming = new Student("小明", "买东西吃");Student xiaozhang = new Student("小张", "打水");Student xiaohong = new Student("小红", "练习");Student xiaohua = new Student("小花", "打羽毛球");//teacher.callDel = xiaoming.DoThing;//teacher.callDel += xiaozhang.DoThing;//teacher.callDel += xiaohong.DoThing;//teacher.callDel += xiaohua.DoThing;//teacher.Call();teacher.RegisterCallEvent(xiaoming.DoThing);teacher.RegisterCallEvent(xiaozhang.DoThing);teacher.RegisterCallEvent(xiaohong.DoThing);teacher.RegisterCallEvent(xiaohua.DoThing);teacher.Call();}}}