为什么是“新的”操作员使用 - =？分离事件处理程序？ [英] Why is "new" operator working for detaching a eventhandler using -=?

问题描述

为什么我必须使用以下内容来分离事件？

  object.myEvent  -  = new MyEvent（EventHandler） ; 
  

我对于新操作符的工作感到非常恼火。 p>

可以解释一下吗？

更新

我已经知道，我不必使用新的操作符来分离事件，但它仍然是Visual Studio 2010中的自动完成建议。我真正的问题是 - =新的工作为分离处理。新的对象/委托如何与先前创建的对象/代理匹配在+ =侧？

解决方案

您没有使用新的运算符。你没有必要，因为C＃2.0出来了：

  foo.SomeEvent + = EventHandler; 
 foo.SomeEvent  -  = EventHandler; 
  

这使用方法组转换从方法组中创建一个委托（方法的名称）。这不仅仅是为了事件：

  Action< string> writeToConsole = Console.WriteLine; 
  

编辑：至于如何有效：

• 在事件上使用 - = 最终会调用删除访问器，通常使用 - = 代表...（至少有效）


• 使用 - = 代表是 代理的语法糖。删除


• Delegate.Remove 使用委托相等 - 两个委托实例相等它们具有相同的方法和相同的目标实例（例如方法）

请注意，使用方法组转换仍将创建一个新的代理人的每个代码实例。

Why do I have to use the following to detach an event?

object.myEvent -= new MyEvent(EventHandler);

I am some how irritated that the new operator is working.

Can some one explain?

Update

I already know that i don't have to use the new operator for detaching events, but it is still the auto complete suggestion in Visual Studio 2010. My real question is how does -= new work for the detach process. How can a new object / delegate match a prior created object / delegate on the += side?

解决方案

You don't have to use the new operator. You haven't had to since C# 2.0 came out:

foo.SomeEvent += EventHandler;
foo.SomeEvent -= EventHandler;

This uses a method group conversion to create a delegate from the method group (the name of the method). This isn't just for events, either:

Action<string> writeToConsole = Console.WriteLine;

EDIT: As for how it works:

• Using -= on an event just ends up calling the "remove" accessor, which typically uses -= on a delegate... (at least effectively)
• Using -= on a delegate is syntactic sugar for Delegate.Remove
• Delegate.Remove uses delegate equality - two delegate instances are equal if they have the same method and the same target instance (for instance methods)

Note that using a method group conversion will still create a new instance of the delegate each time you go through the code.

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