提高在C＃中的事件 [英] Raise an event in C#

问题描述

我碰到这个问题，在Microsoft实践测试来了，我弄糊涂了。这里有一个问题：

I came across this question in a Microsoft Practice Test and I got confused. Here is the question:

这下面的C＃代码示例
是引发一个事件，$ B $的正确方法b假设报警事件时，
AlarmEventArgs类和
AlarmEventHandler代表已经
声明？

Which of the following C# code samples is the proper way to raise an event, assuming that the Alarm event, the AlarmEventArgs class, and the AlarmEventHandler delegate have been declared?

下面是他们提供的正确的答案：

Here is the "correct" answer they provided:

AlarmEventArgs e = new AlarmEventArgs(1, 2);
AlarmEventHandler handler = Alarm; 
if (handler != null) 
{ 
    handler(this, e);
}

不过，也有这似乎是正确的另一个答案。

However, there is also another answer which seems correct.

AlarmEventArgs e = new AlarmEventArgs(1, 2);
if (Alarm!= null) 
{ 
    Alarm (this, e);
}

我个人，总是使用第二种方法。它的工作原理就好了。有人能告诉我为什么我应该使用第一种方法，而不是第二个？

I personally, always use the second method. It works just fine. Can someone please tell me why I should use the first method instead of second?

推荐答案

我问过类似的问题。接受的答案是一个很好的解释。

I asked a similar question. The accepted answer is a good explanation.

的 http://stackoverflow.com/questions/282653/checking-for-null-before-event-dispatching-thread-safe

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