事件 - 命名约定和样式 [英] Events - naming convention and style
问题描述
我正在学习 C# 中的事件/委托.我能否就我选择的命名/编码风格(取自 Head First C# 书籍)征求您的意见?
I'm learning about Events / Delegates in C#. Could I ask your opinion on the naming/coding style I've chosen (taken from the Head First C# book)?
我明天正在教一个朋友这个,并试图想出解释这些概念的最优雅的方式.(认为理解一门学科的最好方法是尝试并教授它!)
Am teaching a friend about this tomorrow, and am trying to come up with the most elegant way of explaining the concepts. (thought the best way to understand a subject is to try and teach it!)
class Program
{
static void Main()
{
// setup the metronome and make sure the EventHandler delegate is ready
Metronome metronome = new Metronome();
// wires up the metronome_Tick method to the EventHandler delegate
Listener listener = new Listener(metronome);
metronome.OnTick();
}
}
<小时>
public class Metronome
{
// a delegate
// so every time Tick is called, the runtime calls another method
// in this case Listener.metronome_Tick
public event EventHandler Tick;
public void OnTick()
{
while (true)
{
Thread.Sleep(2000);
// because using EventHandler delegate, need to include the sending object and eventargs
// although we are not using them
Tick(this, EventArgs.Empty);
}
}
}
<小时>
public class Listener
{
public Listener(Metronome metronome)
{
metronome.Tick += new EventHandler(metronome_Tick);
}
private void metronome_Tick(object sender, EventArgs e)
{
Console.WriteLine("Heard it");
}
}
n.b.代码重构自 http://www.codeproject.com/KB/cs/simplesteventexample.aspx
推荐答案
有几点我想提一下:
Metronome.OnTick 似乎没有正确命名.从语义上讲,OnTick"告诉我它会在Tick"s 时被调用,但这并不是真正发生的事情.我会称它为Go".
Metronome.OnTick doesn't seem to be named correctly. Semantically, "OnTick" tells me it will be called when it "Tick"s, but that isn't really what's happening. I would call it "Go" instead.
通常接受的模型是执行以下操作.OnTick
是一个引发事件的虚方法.这样,您可以轻松覆盖继承类中的默认行为,并调用基类来引发事件.
The typically accepted model, however would be to do the following. OnTick
is a virtual method that raises the event. This way, you can override the default behavior in inherited classes easily, and call the base to raise the event.
class Metronome
{
public event EventHandler Tick;
protected virtual void OnTick(EventArgs e)
{
//Raise the Tick event (see below for an explanation of this)
var tickEvent = Tick;
if(tickEvent != null)
tickEvent(this, e);
}
public void Go()
{
while(true)
{
Thread.Sleep(2000);
OnTick(EventArgs.Empty); //Raises the Tick event
}
}
}
<小时>
另外,我知道这是一个简单的例子,但如果没有附加侦听器,您的代码将抛出 Tick(this, EventArgs.Empty)
.您至少应该包含一个空保护来检查侦听器:
Also, I know this is a simple example, but if there are no listeners attached, your code will throw on Tick(this, EventArgs.Empty)
. You should at least include a null guard to check for listeners:
if(Tick != null)
Tick(this, EventArgs.Empty);
然而,如果监听器在保护和调用之间未注册,这在多线程环境中仍然容易受到攻击.最好的办法是先捕获当前的听众并调用它们:
However, this is still vulnerable in a multithreaded environment if the listener is unregistered between the guard and the invocation. The best would be to capture the current listeners first and call them:
var tickEvent = Tick;
if(tickEvent != null)
tickEvent(this, EventArgs.Empty);
我知道这是一个旧答案,但由于它仍在收集投票,这里是 C# 6 的做事方式.整个守卫"概念可以用条件方法调用代替,并且编译器确实在捕获侦听器方面做了正确的事情(TM):
I know this is an old answer, but since it's still gathering upvotes, here's the C# 6 way of doing things. The whole "guard" concept can be replaced with a conditional method call and the compiler does indeed do the Right Thing(TM) in regards to capturing the listeners:
Tick?.Invoke(this, EventArgs.Empty);
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