活动为什么需要委托？为什么我们甚至需要事件？ [英] Why do Events need Delegates? Why do we even Need Events?

问题描述

我一直搞不清楚过去几周现在有关事件。我理解代表是如何工作的，它不是如何工作的细节，但不够了解，
委托数据类型是一个单播委托。
委托无效是一个多播委托 - 方法的引用清单

我知道一个委托类型编译成一个类，可惜我现在还不能确定如何使用该方法被引用。例如：

 委托无效TestDelegate（）; 
 TestDelegate testDelegate =新TestDelegate（myObject.SomeMethod）; 
  

问题1：我觉得myObject的是目标，并且的someMethod是引用的方法，但我米只传一个输入。
等是myObject.SomeMethod编译为一个字符串，是期间分割字符串？可笑的，我知道。
当你加入一个多播委托

 <$ C：
 
 
 
问题2 $ C> multicastdelegate + = newmethodtobereference 
 multicastdelegate（）; 
  

在调用列表中的每个方法被调用或通知？
。如果这是真的，为什么在的地狱的我需要的事件或事件关键字？难道仅仅是为了告诉嘿，这是作为一个事件的开发商？因为我认真困惑，我只是想在此阶段动议的笑。这是一个示例代码，我写今天要测试它是否我需要事件的关键字或不

 使用系统; 
命名空间LambdasETs 
 {
公众委托无效IsEvenNumberEventHandler（INT numberThatIsEven）; 
 
公共类IsEvenNumberFound 
 {
公共IsEvenNumberEventHandler IsEvenNumberEvent; 
私人诠释数目; 
 
公共无效InputNumber（INT N）
 {
如果（编号％2 == 0）
 {
如果（IsEvenNumberEvent！= NULL）
 {
 IsEvenNumberEvent（N）; 
} 
} 
} 
 
 
公共静态无效的主要（）
 {
 IsEvenNumberFound isEvenNumberFound =新IsEvenNumberFound（）; 
 
 isEvenNumberFound.IsEvenNumberEvent + = IsEvenNumberAction; 
 
 isEvenNumberFound.InputNumber（10）; 
 
到Console.ReadLine（）; 
 
} 
 
公共静态无效IsEvenNumberAction（INT数）
 {
 Console.WriteLine（{0}为偶数！，数）; 
} 
} 
 
 
} 
  

添加事件关键字字段公共IsEvenNumberEventHandler IsEvenNumberEvent; 有没有什么区别。
可以请一些解释，这样一个小白能理解表示感谢。

解决方案

但足够要知道，代表数据类型是单播委托。委托无效是一个多播委托 - 方法的引用清单

事实并非如此。所有正常的代表是多播，即使他们有一个非void返回类型

问题1：我觉得myObject的是目标，并且是的someMethod引用的方法，但我只路过一个输入。所以myObject.SomeMethod编译为一个字符串，是期间分割字符串？可笑的，我知道。

没有， myObject.SomeMethod 是一个方法组。代表实例创建的这种方式包含一点点的编译器的魔力。

multicastdelegate + = newmethodtobereference

如果 multicastdelegate 是一个正常的代理变量，这相当于 multicastdelegate = multicastdelegate + newmethodtobereference 即，它会创建一个新的委托调用的几种方法，并将其分配给 multicastdelegate 。

---

现在你的主要问题：什么是事件的目的

事件有委托类型。它们的行为类似于属性。他们的目的就是封装，特别是他们只让消费者以认购（ + = ）和退订（ - = ），但。不要看事件的值

属性是两种方法的组合： GET 和设置。

事件是两个公共方法的组合订阅和取消，并在现场般的事件也是类似的私人吸气东西的情况。

I've been confused over the past weeks now about events. I understand how delegates work, not how it works in detail but enough to know that delegate datatype is a single cast delegate. delegate void is a multicast delegate - a list of references to methods.

I know a delegate type compiles to a class, but unfortunately I am still not sure how the method is referenced. For example

delegate void TestDelegate();
TestDelegate testDelegate = new TestDelegate(myObject.SomeMethod) ;

Question 1: I think myObject is the target, and SomeMethod is the method to reference, but I'm only passing one input. So is myObject.SomeMethod compiled to a string and is the string split by the period? Ridiculous I know.

Question 2: When you add to a multicast delegate

multicastdelegate+=newmethodtobereference
multicastdelegate() ;

Every method in the invocation list is called or notified? If that's true, why the hell do I need events or the event keyword? Is it simply to tell the developers that Hey, this is acting as an event? Because I'm seriously confused, I just want to move on at this stage lol. This is a sample code I wrote to test it today whether I need event keyword or not.

using System;
namespace LambdasETs
{
    public delegate void IsEvenNumberEventHandler(int numberThatIsEven);

    public class IsEvenNumberFound
    {
        public  IsEvenNumberEventHandler IsEvenNumberEvent;
        private int number;

        public void InputNumber(int n)
        {
            if(number %2 ==0)
            {
                if (IsEvenNumberEvent != null)
                {
                    IsEvenNumberEvent(n);
                }
            }
        }


        public static void Main()
        {
            IsEvenNumberFound isEvenNumberFound = new IsEvenNumberFound();

            isEvenNumberFound.IsEvenNumberEvent += IsEvenNumberAction;

             isEvenNumberFound.InputNumber(10);

            Console.ReadLine();

        }

        public static void IsEvenNumberAction(int number)
        {
            Console.WriteLine("{0} is an even number!", number);
        }
    }


}

Adding the event keyword to the field public IsEvenNumberEventHandler IsEvenNumberEvent; has no difference. Please can some explain so that a noob can understand thanks.

解决方案

but enough to know that delegate datatype is a single cast delegate. delegate void is a multicast delegate - a list of references to methods.

Not true. All "normal" delegates are multicast, even if they have a non void return type.

Question 1: I think myObject is the target, and SomeMethod is the method to reference, but I'm only passing one input. So is myObject.SomeMethod compiled to a string and is the string split by the period? Ridiculous I know.

No, myObject.SomeMethod is a method group. This way of delegate instance creation involves a bit of compiler magic.

multicastdelegate+=newmethodtobereference

If multicastdelegate is a normal delegate variable, this is equivalent to multicastdelegate = multicastdelegate + newmethodtobereference i.e. it creates a new delegate that calls several methods, and assigns it to multicastdelegate.

---

Now to your main question: What's the purpose of events?

Events have delegate types. They behave similarly to properties. Their purpose is encapsulation, in particular they only allow consumers to subscribe(+=) and unsubscribe(-=) but not to read the value of the event.

Properties are a combination of two methods: get and set.

Events are a combination of two public methods subscribe and unsubscribe, and in the case of a field-like event also something similar to a private getter.

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