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委托的注册及注销+观察者模式

article 2024/9/24 3:39:04

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();
        }
    }
    
}