blocks|key|1493557|text|foreach使用枚举器。使用foreach循环的集合必须实现IEnumerable+(或IEnumerable<T>)。然后，foreach调用该集合的GetEnumerator方法，并使用Enumerator遍历该集合。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1493558|entityMap^0|V|B|19|E|2O|A|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|O|8|@]|D|@]|E|$]]]|G|$]]

foreach uses an enumerator.
The collection over which you loop using foreach, has to implement <code>IEnumerable</code> (or <code>IEnumerable&lt;T&gt;</code>).
Then, foreach calls the GetEnumerator method of that collection, and uses the <code>Enumerator</code> to traverse the collection.

blocks|key|309900|text|在大多数情况下，foreach针对实时集合(无显式克隆)工作，如果您在枚举集合时尝试更改集合，则枚举器会中断并引发异常。因此，如果您要添加到Pages中，请预料到会出现问题。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|309901|entityMap^0|8|7|1Y|5|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

In most cases, <code>foreach</code> works against the live collection (no explicit clone), and if you try to change the collection while enumerating it, then the enumerator breaks with an exception. So if you are adding to <code>Pages</code>, expect problems.

blocks|key|309929|text|看起来代码并没有修改Pages集合，而是修改了Pages集合中Page对象中对象的内容。至少具有类似集合的方法的Page类型。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|309930|一般来说，每个集合都以适合自己的方式实现迭代，并且在迭代时通常是不可修改的，但可以通过获取自身的快照来实现迭代的集合。|309931|没有检测循环退出的机制，这将允许在该点采取操作(考虑这将如何与循环主体中的异常、中断和返回进行交互)。|309932|entityMap^0|A|5|N|5|V|4|1K|4|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@$9|M|A|N|B|C]|$9|O|A|P|B|C]|$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|U|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|V|8|@]|D|@]|E|$]]|$1|J|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|K|$]]

It looks like the code doesn't modify the <code>Pages</code> collection, but the content of the objects in the <code>Page</code> objects in the <code>Pages</code> collection. The <code>Page</code> type having at least collection like method.

In general each collection implements iteration in a way suitable for itself, and generally becomes unmodifiable while iterating, but one could implelment a collection which iterates by taking a snapshot of itself.

There is no mechanism to detect exit from a loop which would allow action to be taken at that point (consider how this would interact with exceptions, break and return in the body of the loop).

blocks|key|1611845|text|我非常确定您会抛出一个异常，抱怨底层集合已被修改|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1611846|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|$]]

I'm pretty sure you'll get an exception thrown complaining that the underlying collection was modified

blocks|key|88800|text|您没有修改您正在枚举的集合，因此使用此代码不会有任何问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|88801|如果正在枚举集合的克隆，这也是不相关的，因为集合和克隆包含的对象仍然是相同的(引用等于)。|88802|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 are not modifying the collection you are enumerating, therefore you won't have any problems with this code.

It is also irrelevant, if an clone of the collection is being enumerated, because the objects contained by both, collection and clone, are still the same (reference equals).

blocks|key|1611888|text|我认为最安全的方法是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1611889|Array<Page>+newpages+=+new+Array<Page>();++++
foreach(Page+page+in+pages)
{
++++newpages.AddRange(RetrieveSubPages(page.Id));
}

pages.AddRange(newpages);|code-block|syntax|javascript|1611890|如果您想要递归到子页面中，则必须扩展一下这一点。|1611891|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I think the safest way is this:

<pre><code>Array&lt;Page&gt; newpages = new Array&lt;Page&gt;(); 
foreach(Page page in pages)
{
 newpages.AddRange(RetrieveSubPages(page.Id));
}

pages.AddRange(newpages);
</code></pre>

You'd have to extend this a bit if you wanted to recurse into the subpages.

blocks|key|310015|text|在回答您的问题时，它不会复制。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|310016|它创建一个枚举数并遍历集合。如果在此枚举发生时，在foreach本身中或异步地更改了集合，您将得到一个异常：|310017|mscorlib.dll中出现'System.InvalidOperationException‘类型的未经处理的异常|310018|附加信息:集合已修改；枚举操作可能无法执行。|310019|您可以使用临时集合并在以后连接这两个集合，也可以不使用枚举器。|310020|++++for+(int+i+=+0;+i+<+pages.Count;+i%2B%2B)
++++{
++++++++test.AddRange(RetrieveSubPages(pages[i].Id));
++++}|code-block|syntax|javascript|310021|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|S|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|T|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|U|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|V|8|@]|9|@]|A|$M|N]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

In response to you question, it does not make a copy. 

It creates an enumerator and iterates through the collection. If the collection is changed while this enumeration is happening, in the foreach itself, or asynchronously, you will get an exception:

An unhandled exception of type 'System.InvalidOperationException' occurred in mscorlib.dll

Additional information: Collection was modified; enumeration operation may not execute.

You can, use a temporary collection and join the two afterwards, or just not use an enumerator.

<pre><code> for (int i = 0; i &lt; pages.Count; i++)
 {
 test.AddRange(RetrieveSubPages(pages[i].Id));
 }
</code></pre>

This is the situation:

I'm browsing through some code and I wondered if the following statement takes a reference of the selected collection or a copy with which it replaces the original object when the foreach loop finishes. If the first, will it take the new found pages and join them in the loop?

<pre><code>foreach(Page page in Pages)
{
 page.AddRange(RetrieveSubPages(page.Id));
}
</code></pre>

Edit: I'm sorry, I made a typo.

It should be this:

<pre><code>foreach(Page page in pages)
{
 pages.AddRange(RetrieveSubPages(page.Id));
}
</code></pre>

What i tried to say is that if i add some objects to the enumerating collection, will it join those objects in the foreach?

Foreach while adding items to the looping collection

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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情况是这样的：我正在浏览一些代码，我想知道下面的语句是接受所选集合的引用，还是在foreach循环结束时用来替换原始对象的副本。如果是第一个，它会将新找到的页面加入到循环中吗？foreach(Page page in Pages){    page.AddRange(RetrieveSubPages(page.Id))...

问将项添加到循环集合时的Foreach
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