blocks|key|3466960|text|如果我要执行一个已经指定了类型的|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3466961|循环，为什么要在ArrayList上使用ToArray(类型)呢？|blockquote|3466962|3466963|3466964|一般来说，您可能不想这样做。调用ToArray()实际上会创建一个新的值数组。|offset|length|style|CODE|3466965|如果您的循环要修改ArrayList，那么这样做可能会有好处。你不能在枚举时修改大多数集合，所以你会得到一个异常。通过添加ToArray调用，可以枚举集合的副本(作为数组)，因此可以修改原始集合。|3466966|注意，一般来说，如果是这样的话，我会使用ToList()，而不是ToArray()，因为它通常会更高效一些(通常会减少一个内存分配)。我还建议在任何新代码中使用List(Of+Integer)而不是ArrayList，因为这样可以保证类型安全。|3466967|entityMap^0|0|0|0|0|G|9|0|9|9|1P|7|0|K|8|W|9|28|G|2R|9|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$]]|$1|E|3|-4|5|6|7|U|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|V|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|W|8|@$I|X|J|Y|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|Z|8|@$I|10|J|11|K|L]|$I|12|J|13|K|L]]|9|@]|A|$]]|$1|O|3|P|5|6|7|14|8|@$I|15|J|16|K|L]|$I|17|J|18|K|L]|$I|19|J|1A|K|L]|$I|1B|J|1C|K|L]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]]|R|$]]

<blockquote>
 Why would I want to use ToArray(type) on an ArrayList if I will be doing a For Each loop where the type is already specified?
</blockquote>

In general, you likely don't want to do this. Calling <code>ToArray()</code> actually creates a new array of your values.

The one place where this could be beneficial is if your loop is going to modify the <code>ArrayList</code>. You can't modify most collections while enumerating them, so you'd get an exception. By adding the <code>ToArray</code> call, you are enumerating a copy of the collection (as an array), so you can modify the original.

Note that, in general, if that's the case, I'd use <code>ToList()</code>, and not <code>ToArray()</code>, as it's typically a bit more efficient (often one fewer memory allocation). I'd also recommend using <code>List(Of Integer)</code> instead of <code>ArrayList</code> for any new code, as you get type safety.

blocks|key|1496660|text|您不需要在For+each循环中的ArrayList上调用ToArray：i已经声明为Integer，因此将自动为您执行类型转换。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1496661|有时，您可能需要对查询结果调用数组，以便将数据复制到内存中。它的一个优点是将数据库查询的结果复制到内存中，因为您可以更快地关闭连接。此外，当查询引用已修改的变量时，或者当多次生成IEnumerable的代价很高时，调用ToList可以帮助您。|1496662|entityMap^0|5|8|H|9|T|7|11|1|17|7|0|2H|B|31|6|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$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|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|I|$]]

You do not need to call <code>ToArray</code> on an <code>ArrayList</code> in a <code>For each</code> loop: <code>i</code> is already declared as <code>Integer</code>, so the type conversion will be performed for you automatically.

Sometimes you may need to call an array on results of a query to copy the data into memory. One place where it gives you advantages is copying results of a database query into memory, because you can close the connection sooner. In addition, calling <code>ToList</code> could help you in situations when a query would otherwise reference a modified variable, or when <code>IEnumerable</code> is expensive to produce multiple times.

blocks|key|1494119|text|在该ArrayList上调用.ToArray()有两个原因：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1494120|1494121|，因此您不需要在ArrayList中强制转换项。数组是强类型的，因此将它们放在第一位意味着编译器知道数组列表中的所有内容都是整数。|ordered-list-item|1494122|，这样您就可以将数组列表传递给需要数组作为参数的方法。|1494123|1494124|entityMap^0|E|A|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|R|8|@]|D|@]|E|$]]|$1|G|3|H|5|I|7|S|8|@]|D|@]|E|$]]|$1|J|3|K|5|I|7|T|8|@]|D|@]|E|$]]|$1|L|3|-4|5|6|7|U|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

There are two reasons you might call <code>.ToArray()</code> on that ArrayList:

<ol>
<li>So you don't need to cast the items in the ArrayList. The array is strongly typed, and so putting them there first means the compiler knows that everything in the arraylist is an integer.</li>
<li>So you could pass the arraylist to a method that expects an array as argument.</li>
</ol>

blocks|key|353528|text|在旧的代码库中进行防御性编程。大概当时他们还没有可用的"List(Of+Integer)“。有几个原因让你希望在"For+Each“语句中失败(如果”in“包含一个非Integer)，而不是在循环的后面：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|353529|353530|显然，你不想浪费时间。循环中的操作可能需要很长时间。在开始循环之前失败要比在迭代99999中失败要好。|ordered-list-item|353531|您可能想要在整个ArrayList上执行“全部或不执行”操作。|353532|353533|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|L|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|M|8|@]|9|@]|A|$]]|$1|F|3|G|5|E|7|N|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|P|8|@]|9|@]|A|$]]]|J|$]]

Defensive programming in an old code base. Presumably they didn't have "List(Of Integer)" available at the time. There are a couple reasons you want to fail at the "For Each" statement (if "ints" contains a non-Integer) rather than later on in the loop:

<ol>
<li>Obviously, you don't want to waste time. The operations inside the loop may take a long time. Better to fail before beginning the loop than at iteration 99999.</li>
<li>You may want to do "all or none" of the operations on the whole ArrayList.</li>
</ol>

blocks|key|3467153|text|在您的情况下，更改为此代码，您不需要：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3467154|Dim+i+As+Integer
Dim+ints+As+New+Generic.List(Of+Integer)
ints.Add(1)
'...+lets+say+we+add+more+Integers

For+each+i+in+ints
'Do+something
Next|code-block|syntax|javascript|3467155|在处理LINQ结果时，ToArray很方便。如果您的集合大小是可测量的，则可以执行ToArray。大多数较旧的.NET函数更喜欢使用数组。String.Join就是一个很好的例子。因此，您可能需要经常使用它来实现调用之间的类型兼容性。这样做的另一个原因是在调试器中更容易检查数组。|offset|length|style|CODE|3467156|在任何情况下，你都应该证明这种需求是合理的。如果您的目标是严格类型，最好使用为此目的而创建的类型，例如上面的Generic.List(Of+T)。|3467157|entityMap^0|0|0|B|7|15|7|1X|B|0|1I|I|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@$I|T|J|U|K|L]|$I|V|J|W|K|L]|$I|X|J|Y|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|Z|8|@$I|10|J|11|K|L]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|P|$]]

In your case, change to this code and you don't need to:

<pre><code>Dim i As Integer
Dim ints As New Generic.List(Of Integer)
ints.Add(1)
'... lets say we add more Integers

For each i in ints
'Do something
Next
</code></pre>

<code>ToArray</code> comes handy when dealing with LINQ results. If your collection size is measurable, you can do <code>ToArray</code>. Most older .NET functions prefer to use arrays. Good example is <code>String.Join</code>. So you may need to use it often for type compatibility between calls. Another reason to do so is that arrays are easier to inspect in debugger.

In any case, you should always justify the need. If your goal is strict typing, better use types that were created for this purpose, such as the above <code>Generic.List(Of T)</code>.

The code base where I work has code similar to the following in a few places:

<pre><code>Dim i As Integer
Dim ints As New ArrayList
ints.Add(1)

'... lets say we add more Integers

For each i in ints.ToArray(GetType(Integer))
'Do something
Next
</code></pre>

I'm wondering what benefit is gained from the <code>.ToArray(GetType(Integer))</code> since omitting that has nearly the same result at run-time. That is calling <code>For Each i In ints</code>. The only difference I see is that if some type other than Integer is in the <code>ArrayList</code> the resulting error message is more helpful if you do not call <a href="http://msdn.microsoft.com/en-us/library/fcyyh2hb.aspx" rel="nofollow">.ToArray()</a>

Why would I want to use <code>ToArray(type)</code> on an <code>ArrayList</code> if I will be doing a <code>For Each</code> loop where the type is already specified?

Why should I call ArrayList.ToArray?

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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在我工作的代码库中，有几个地方的代码类似于以下代码：Dim i As IntegerDim ints As New ArrayListints.Add(1)'... lets say we add more IntegersFor each i in ints.ToArray(GetType(Integer))'Do ...

问为什么我要调用ArrayList.ToArray？
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问为什么我要调用ArrayList.ToArray？EN