c# 委託和事件

事件：事件是委託的安全包裹，讓委託更加安全 是一種特色的變數型別

事件只能用+= -=來，而委託還可以用= 或者new來賦值

委託：以方法形式呼叫 ; 也可以+=，-=形式呼叫

  
  //以方法引數形式呼叫

  SayHello("小紅", chinesehHello);


   //以+=， -=方式呼叫

    HelloDelegate helloDelegate = new HelloDelegate(chinesehHello);
    helloDelegate += englishHello;
    SayHello("wenyu", helloDelegate);

    helloDelegate -= englishHello;
    SayHello("wenyu2", helloDelegate);


//==================

        public delegate void HelloDelegate(string name);

        public void SayHello(string name, HelloDelegate helloDelegate)
        {
            helloDelegate(name);
        }

        public void englishHello(string name)
        {
            helloList.Add($"hello,{name}");
            Console.WriteLine($"hello,{name}");
        }
        public void chinesehHello(string name)
        {
            helloList.Add($"你好,{name}");

            Console.WriteLine($"你好,{name}");
        }

//事件：事件是委託的安全包裹，讓委託更加安全 是一種特色的變數型別
//事件只能用+= -=來，而委託還可以用= 或者new來賦值

                Publisher publisher = new Publisher();
                Subscriber subscriber = new Subscriber();

                //事件：事件是委託的安全包裹，讓委託更加安全 是一種特色的變數型別
                //事件只能用+= -=來，而委託還可以用= 或者new來賦值

                publisher.addEvent += subscriber.addEmployee;
                publisher.addEvent += subscriber.deleteEmployee;
                //publisher.addEvent("");//不能直接使用 ×
                var result1 = publisher.executeEvent("我是event呼叫的"); //事件只能在宣告的類裡面呼叫



                publisher.addDelegate += subscriber.addEmployee;
                publisher.addDelegate += subscriber.deleteEmployee;

                //會呼叫add,delete方法，但是返回只返回最後一個方法的返回值
                var result2 = publisher.addDelegate("我是delegate呼叫的");



//==========================


    public delegate string MyDelegate(string msg);
    public class Publisher
    {
        //事件作為成員變數存在於類中 ; 事件不能在類外面賦值+=  -=  ;事件不能在類外面出發呼叫
        public event MyDelegate addEvent;
        public MyDelegate addDelegate;
        public string executeEvent(string msg)
        {
            //addEvent?.Invoke(msg);
            return addEvent(msg);
        }
    }
    public class Subscriber
    {
        public string addEmployee(string msg)
        {
            return $"addEmployee：{msg}";
        }
        public string deleteEmployee(string msg)
        {
            return $"deleteEmployee：{msg}";
        }
    }