blocks|key|2487795|text|前面的注释都没有解决两者之间最重要的区别:+KeyedCollection保持项目的添加顺序(添加的第一个项目在索引0处，最后添加的项目在最后一个索引处)。字典不会(或者至少它永远不会保证这样做)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2487796|KeyedCollection的这一额外优势确实具有很小的性能成本。在幕后，您需要支付维护一个字典和一个列表的费用。|2487797|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|$]]

None of the previous comments address the most important difference between the two:
KeyedCollection keeps your items in the order in which they are added (the first item added is at index 0 and the last added is at the last index). Dictionary does not (or at least it is never guaranteed to do so).

This extra benefit of KeyedCollection does have a small performance cost. Under the covers, you pay the cost of maintaining both a Dictionary and a List.

blocks|key|4598743|text|这里很好地解释了字典和KeyedCollection之间的差异：http://geekswithblogs.net/NewThingsILearned/archive/2010/01/07/using-keyedcollectionlttkey-titemgt.aspx|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4598744|要点是：|4598745|4598746|KeyedCollection是抽象的，所以你不能使用它directly.|unordered-list-item|4598747|KeyedCollection在情况下很有用，当键在实体本身中时，你可以在集合中封装键检索implementation.|4598748|There是KeyedCollection的通用实现(虽然不在框架中)，它允许你在集合构造函数中粘贴键检索委托，所以你不必在每次添加项时重复它。|4598749|4598750|更新:只要文章的原始链接被删除，就会添加到web存档的链接：https://web.archive.org/web/20200228045828/http://geekswithblogs.net/NewThingsILearned/archive/2010/01/07/using-keyedcollectionlttkey-titemgt.aspx|4598751|entityMap|0|LINK|mutability|MUTABLE|url|http://geekswithblogs.net/NewThingsILearned/archive/2010/01/07/using-keyedcollectionlttkey-titemgt.aspx|1|https://web.archive.org/web/20200228045828/http://geekswithblogs.net/NewThingsILearned/archive/2010/01/07/using-keyedcollectionlttkey-titemgt.aspx^0|W|2V|0|0|0|0|0|0|0|0|U|42|1|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|6|7|14|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|15|8|@]|9|@]|C|$]]|$1|G|3|H|5|I|7|16|8|@]|9|@]|C|$]]|$1|J|3|K|5|I|7|17|8|@]|9|@]|C|$]]|$1|L|3|M|5|I|7|18|8|@]|9|@]|C|$]]|$1|N|3|-4|5|6|7|19|8|@]|9|@]|C|$]]|$1|O|3|P|5|6|7|1A|8|@]|9|@$A|1B|B|1C|1|1D]]|C|$]]|$1|Q|3|-4|5|6|7|1E|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]|Y|$5|T|U|V|C|$W|Z]]]]

Here is good explanation about differences between Dictionary and KeyedCollection: <a href="http://geekswithblogs.net/NewThingsILearned/archive/2010/01/07/using-keyedcollectionlttkey-titemgt.aspx" rel="nofollow noreferrer">http://geekswithblogs.net/NewThingsILearned/archive/2010/01/07/using-keyedcollectionlttkey-titemgt.aspx</a>
Main points are:
<ul>
<li>KeyedCollection is abstract, so you can't use it directly.</li>
<li>KeyedCollection is useful for cases, when key is in entity itself, then you can encapsulate key retrieval within collection implementation.</li>
<li>There are generic implementations for KeyedCollection (not in the framework though), which allow you to paste key retrieval delegate in collection constructor, so you don't have to repeat it each time you add item.</li>
</ul>
Update: as long as original link to article was removed, adding link to web archive: <a href="https://web.archive.org/web/20200228045828/http://geekswithblogs.net/NewThingsILearned/archive/2010/01/07/using-keyedcollectionlttkey-titemgt.aspx" rel="nofollow noreferrer">https://web.archive.org/web/20200228045828/http://geekswithblogs.net/NewThingsILearned/archive/2010/01/07/using-keyedcollectionlttkey-titemgt.aspx</a>

blocks|key|2487845|text|KeyedCollection允许使用可变密钥和管理密钥更改的方法。字典不允许更改键。其次，如果你有一个需要查找的集合，从实体中提取关键字的逻辑仍然保留在一个地方-而维护字典将需要将关键字提取逻辑放在每个向字典添加项/从字典中删除项的位置。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2487846|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|$]]

A KeyedCollection allows mutable keys and ways to manage change in key. Dictionary does not allow changes to key. Secondly, if you have a collection which needs lookup, the logic to extract key from entity remains in one place - whereas maintaining dictionary will need to put key extraction logic at each place where items are added/removed from dictionary.

blocks|key|1863967|text|默认情况下，KeyedCollection在幕后创建一个字典。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1863968|如果键还具有作为值的一部分的含义，并且还定义了唯一性，那么这就是KeyedCollection的用途。|1863969|如果你想修改字典备份，那么使用这个ctor：|1863970|protected+KeyedCollection(
IEqualityComparer<TKey>+comparer,
int+dictionaryCreationThreshold)|code-block|syntax|javascript|1863971|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|O|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|P|8|@]|9|@]|A|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

By default a KeyedCollection creates a Dictionary under the covers. 
If the Key also has meaning as part of the Value and also defines uniqueness then that is the purpose of a KeyedCollection. 

If you want to modify the dictionary backing then use this ctor:

<pre><code>protected KeyedCollection(
IEqualityComparer&lt;TKey&gt; comparer,
int dictionaryCreationThreshold)
</code></pre>

blocks|key|2487878|text|当密钥在项本身上时，应该使用KeyedCollection。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2487879|默认情况下，KeyedCollection是字典的Collection<TItem>包装器。当您使用小集合和/或更喜欢直接检索项时，接受dictionaryCreationThreshold参数的KeyedCollection+provides+a+constructor指示切换到Dictionary的集合计数。|2487880|KeyedCollection的另一个方面是，您可以选择切换key属性(只要它们的类型匹配)。从性能上讲，我不认为包装字典有太多开销，除非你生成了一堆KeyedCollection实例，或者如果你使用非常大的集合(有一些内部null检查来确定是否有字典)。|2487881|我希望在KeyedCollection中看到的一件事是将其取消abstract，但您可以同样简单地创建一个通用的混凝土类型。|2487882|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/Microsoft/referencesource/blob/master/mscorlib/system/collections/objectmodel/keyedcollection.cs#L34^0|E|F|0|6|F|P|H|1W|R|2Q|F|3X|A|36|M|0|0|0|F|23|F|34|4|0|4|F|V|8|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@$9|17|A|18|1|19]]|E|$]]|$1|H|3|I|5|6|7|1A|8|@$9|1B|A|1C|B|C]|$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|1H|8|@$9|1I|A|1J|B|C]|$9|1K|A|1L|B|C]]|D|@]|E|$]]|$1|L|3|-4|5|6|7|1M|8|@]|D|@]|E|$]]]|M|$N|$5|O|P|Q|E|$R|S]]]]

A <code>KeyedCollection</code> should be used when the key is on the item itself.

By default, <code>KeyedCollection</code> is a <code>Collection&lt;TItem&gt;</code> wrapper around a dictionary. When you use small collections and/or you prefer retrieving items directly, the <code>KeyedCollection</code> <a href="https://github.com/Microsoft/referencesource/blob/master/mscorlib/system/collections/objectmodel/keyedcollection.cs#L34" rel="nofollow noreferrer">provides a constructor</a> that takes a <code>dictionaryCreationThreshold</code> parameter, that indicates at what collection count to switch to <code>Dictionary</code>. 
Another aspect in <code>KeyedCollection</code> is that you can choose to switch the key property (as long as their types match). This can be good for double keyed items etc.
Performancewise, I don't think wrapping a dictionary has much overhead except if you generate a bunch of <code>KeyedCollection</code> instances, or if you use really large collections (there are some internal <code>null</code> checks to determine if there is a dictionary). 
One thing I'd hope to see in <code>KeyedCollection</code> is un<code>abstract</code>ing it, but you can make a generic concrete type just as easy.

blocks|key|4598696|text|您不能使用KeyedCollection，因为它是抽象的：http://msdn.microsoft.com/en-us/library/ms132438.aspx。这意味着你不能创建它的对象。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4598697|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/ms132438.aspx^0|T|1H|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

You can't use KeyedCollection because it's abstract: <a href="http://msdn.microsoft.com/en-us/library/ms132438.aspx" rel="nofollow">http://msdn.microsoft.com/en-us/library/ms132438.aspx</a>. This means you can't create an object of it.

I have a class (<code>SomeClass</code>) which contains a property <code>Name</code> of <code>string</code> type. And I need to store an array of that class and find its items by their names. For this purpose there are two types of collections: <code>KeyedCollection</code> and <code>Dictionary</code>. My question is: What difference between them and in such case It is better to use <code>KeyedCollection</code> and <code>Dictionary</code>? Thanks for any help in explanation.

Dictionary or KeyedCollection?

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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我有一个包含string类型的属性Name的类(SomeClass)。我需要存储该类的一个数组，并根据它们的名称查找它们的项。为此，有两种类型的集合：KeyedCollection和Dictionary。我的问题是:它们之间有什么区别，在这种情况下，使用KeyedCollection和Dictionary更好？感谢您的任何帮助的解释。

问字典还是KeyedCollection？
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问字典还是KeyedCollection？
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