blocks|key|1510232|text|您可以将function()关键字看作一个构造函数，每次创建一个新对象(闭包)。因此，如果您只将闭包创建为一个参数，而没有在任何地方保留引用，那么就没有办法在其他地方获得“相同”的闭包。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1510233|最明显的解决方案是你不喜欢的，在使用函数之前定义它。当然，它仍然可以是一个完整的闭包，而不仅仅是一个“静态的”函数。只需在您想要的上下文中定义它，并将其分配给一个局部变量。|1510234|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

You can think of the function() keyword as a constructor, creating a new object (a closure) each time. Therefore, if you create the closure just for as a parameter and don't retain a reference anywhere, there's no way to get a hold of "the same" closure somewhere else.

The obvious solution is what you don't like, defining the function before using it. Of course, it can still be a full closure and not just a 'static-like' function. simply define it in the context you want, and assign it to a local variable.

blocks|key|1725375|text|我不确定这是否会奏效，但值得一试：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1725376|root.removeEventListener("click",+arguments.callee+);|code-block|syntax|javascript|1725377|有关它的更多信息，请访问Flex+lang+ref。|offset|length|1725378|entityMap|0|LINK|mutability|MUTABLE|url|http://livedocs.adobe.com/flex/2/langref/arguments.html#callee^0|0|0|C|D|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

I'm not sure if this will work but its worth a shot: 

<pre><code>root.removeEventListener("click", arguments.callee );
</code></pre>

More information about it can be found <a href="http://livedocs.adobe.com/flex/2/langref/arguments.html#callee" rel="nofollow noreferrer">Flex lang ref</a>

blocks|key|1725414|text|下面是删除我在生产项目中使用过的事件侦听器的一般方法|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1725415|addEventListener
(
++++Event.ACTIVATE,+
++++function(event:Event):void
++++{
++++++++(event.target+as+EventDispatcher).removeEventListener(event.type,+arguments.callee)+++++++++++++
++++}
)|code-block|syntax|javascript|1725416|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Here's a generic way of removing event listeners that i have used on production projects

<pre><code>
addEventListener
(
 Event.ACTIVATE, 
 function(event:Event):void
 {
 (event.target as EventDispatcher).removeEventListener(event.type, arguments.callee) 
 }
)
</code></pre>

blocks|key|1725465|text|这只是我在Adobe网站上的Flex+in+a+Week教程中遇到的关于你的代码的附带说明。在那里，他们说你应该总是使用事件类型的常量，而不是字符串。这样你就能得到打字错误的保护。如果您在事件类型字符串中输入错误(例如"clse")，您的事件处理程序将被注册，但当然不会被调用。取而代之的是使用Event.CLOSE，这样编译器就会捕捉到拼写错误。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1725466|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Just a side note on your code that I came across in the Flex In A Week set of tutorials on the Adobe web site. There, they said you should always use the constants for the event types rather than the string. That way you get typo protection. If you make a typo in the event type string (like say "clse"), your event handler will get registered but of course never invoked. Instead, use Event.CLOSE so the compiler will catch the typo.

blocks|key|1510450|text|我不知道您实际在做什么，但在这个特定的示例中，您可能会有一个_clickEnabled全局变量。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1510451|然后，在事件处理程序中，您只需检查_clickEnabled，如果为false，则立即执行return。|offset|length|style|CODE|1510452|然后，您可以启用和禁用整个事件，而无需分离和重新附加它。|1510453|entityMap^0|0|19|6|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@$D|N|E|O|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|K|$]]

I dont know what you're actually doing but in this particular example perhaps you could have a _clickEnabled global variable.

Then inside the event handler you just check _clickEnabled, and if its false you just <code>return</code> immediately.

Then you can enable and disable the overall event without detaching and reattaching it.

blocks|key|1510458|text|我有时会用到这个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1510459|var+closure:Function+=+null;
root.addEventListener("click",+
+++closure+=+function+()+
+++{+
++++++navigateToURL(ClickURLRequest,"_self");+
+++});

root.removeEventListener("click",+closure);|code-block|syntax|javascript|1510460|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I use this sometimes:

<pre><code>var closure:Function = null;
root.addEventListener("click", 
 closure = function () 
 { 
 navigateToURL(ClickURLRequest,"_self"); 
 });

root.removeEventListener("click", closure);
</code></pre>

blocks|key|1510501|text|如前所述，您可以从闭包本身的侦听器链中删除闭包。这是通过使用arguments.callee完成的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1510502|myDispatcher.addEventListener("click",+function(event:Event):void
{
++++IEventDispatcher(event.target).removeEventListener(event.type,+arguments.callee);

++++//+Whatever+else+needs+doing+goes+here
});|code-block|syntax|javascript|1510503|这将有效地将闭包转换为事件的一次性侦听器，只需在事件触发后将其自身分离。虽然在语法上冗长，但对于那些真正只触发一次(或者你只关心一次)的事件来说，它是一种令人难以置信的有用技术，例如，在Flex中使用"creationComplete“。在下载数据时，我一直在使用它，因为我认为内联回调代码会更容易理解。这就像隐藏了异步性：|1510504|myLoader.addEventListener("complete",+function(event:Event):void
{
++++/*+Even+though+the+load+is+asynchronous,+having+the+callback+code+inline
+++++*+like+this+instead+of+scattered+around+makes+it+easier+to+understand,
+++++*+in+my+opinion.+*/
});|1510505|但是，如果您想要多次监听事件，由于显而易见的原因，这将不会非常有效。在这种情况下，您需要在某个地方存储对闭包的引用。方法与ActionScript中的任何其他对象一样，都是可以传递的对象。因此，我们可以将代码修改为如下所示：|1510506|var+closure:Function;

myDispatcher.addEventListener("click",+function(event:Event):void
{
++++closure+=+arguments.callee;

++++//+Whatever+else+needs+doing+goes+here
});|1510507|当您需要删除事件侦听器时，使用'closure‘引用，如下所示：|1510508|myDispatcher.removeEventListener("click",+closure);|1510509|显然，这是一个抽象的例子，但是使用像这样的闭包是非常有用的。但是，它们也有缺点，比如效率低于命名方法。另一个缺点是，如果需要的话，您实际上必须存储对闭包的引用。然后，必须注意保持该引用的完整性，就像任何其他变量一样。|1510510|因此，虽然不同的语法可能有其用途，但它并不总是最好的解决方案。这是一种苹果和橙子之类的东西。|1510511|entityMap^0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|12|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|14|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|S|3|T|5|6|7|16|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|17|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|X|$]]

As has already been suggested, you may remove the closure from the chain of listeners from within the closure itself. This is done through the use of arguments.callee:

<pre><code>myDispatcher.addEventListener("click", function(event:Event):void
{
 IEventDispatcher(event.target).removeEventListener(event.type, arguments.callee);

 // Whatever else needs doing goes here
});
</code></pre>

This will effectively turn the closure into a one-time listener of the event, simply detaching itself once the event has fired. While syntactically verbose, it's an incredibly useful technique for those many events that really only fire once (or that you only care about once) like "creationComplete" in Flex, for instance. I use this all the time when downloading data, since I think having the callback code inline makes it easier to understand. It is like hiding away the asynchronous-ness:

<pre><code>myLoader.addEventListener("complete", function(event:Event):void
{
 /* Even though the load is asynchronous, having the callback code inline
 * like this instead of scattered around makes it easier to understand,
 * in my opinion. */
});
</code></pre>

However, if you want to listen to the event multiple times, this will not be very effective for obvious reasons. In that case, you need to store a reference to the closure somewhere. Methods are objects like anything else in ActionScript and can be passed around. Thus, we can alter our code to look like this:

<pre><code>var closure:Function;

myDispatcher.addEventListener("click", function(event:Event):void
{
 closure = arguments.callee;

 // Whatever else needs doing goes here
});
</code></pre>

When you need to remove the event listener, use the 'closure' reference, like so:

<pre><code>myDispatcher.removeEventListener("click", closure);
</code></pre>

Obviously, this is an abstract example but using closures like this can be pretty useful. They do have drawbacks though, such as being less efficient than named methods. Another drawback is the fact that you actually have to store away a reference to the closure if you ever need it. Care must then be taken to preserve the integrity of that reference, just like with any other variable.

Thus, while the different syntax may have its uses, it's not always the best solution. It's an apples and oranges kind of thing.

I tried doing this:

<pre><code>root.addEventListener("click", 
 function () 
 { 
 navigateToURL(ClickURLRequest,"_self"); 
 });
</code></pre>

And it does add the event listener. I like using closures because they work well in this situation,

however, removing the event listener requires a reference to the original function, and since I used an anonymous closure, it does not work, I tried:

<pre><code> root.removeEventListener("click", 
 function () 
 { 
 navigateToURL(ClickURLRequest,"_self"); 
 });
</code></pre>

as well as:

<pre><code> root.removeEventListener("click", function () {} );
</code></pre>

The only way I found it would work was to ditch the anonymous closure and point the event listeners at a pre-existing function:

<pre><code> function OnClick (e:Event)
 {
 navigateToURL(ClickURLRequest,"_self");
 }

 root.addEventListener("click", OnClick);
 root.removeEventListener("click", OnClick);
</code></pre>

Does anyone know a way to use anonymous closures for event handlers while still retaining the ability to remove them?

ActionScript 3.0 using closures for event handlers

编译器

我试过这样做：root.addEventListener("click",    function ()    {       navigateToURL(ClickURLRequest,"_self");    });并且它确实添加了事件侦听器。我喜欢使用闭包，因为它们在这种情况下工作得很好。但是，删除事件侦听器需要...

问为事件处理程序使用闭包的ActionScript 3.0
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