如何获得ReadOnlyCollection还< T> T，S>该键在Dictionary&LT的; [英] How to get a ReadOnlyCollection<T> of the Keys in a Dictionary<T, S>

问题描述

我的类包含一个词典< T，S>字典，我要揭露一个 ReadOnlyCollection还< T> 的关键。我怎么能做到这一点不复制词典< T，S> .KeyCollection dict.Keys 到一个数组，然后露出了数组作为 ReadOnlyCollection还？

My class contains a Dictionary<T, S> dict, and I want to expose a ReadOnlyCollection<T> of the keys. How can I do this without copying the Dictionary<T, S>.KeyCollection dict.Keys to an array and then exposing the array as a ReadOnlyCollection?

我要的 ReadOnlyCollection还是一个合适的包装，即得。以反映底层词典变化，据我了解复制集合到一个数组是不会这样做的（以及低效似乎 - 我其实不愿意一个新的集合，只是揭露键底层集合.. ）。任何想法，将不胜感激。

I want the ReadOnlyCollection to be a proper wrapper, ie. to reflect changes in the underlying Dictionary, and as I understand it copying the collection to an array will not do this (as well as seeming inefficient - I don't actually want a new collection, just to expose the underlying collection of keys...). Any ideas would be much appreciated!

编辑：我使用C＃2.0，因此不具备扩展方法，如.ToList（容易）可用。

I'm using C# 2.0, so don't have extension methods such as .ToList (easily) available.

推荐答案

如果你真的想使用ReadOnlyCollection还< T>中，问题是，ReadOnlyCollection还与LT的构造; T>需要一个IList< T> ;,而词典的KeyCollection只是一个ICollection的< T>

If you really want to use ReadOnlyCollection<T>, the issue is that the constructor of ReadOnlyCollection<T> takes an IList<T>, while the KeyCollection of the Dictionary is only a ICollection<T>.

所以，如果你想换行KeyCollection在ReadOnlyCollection还你将不得不创建一个适配器（或包装）类型，实施的IList< T> ;,包裹KeyCollection。因此，它看起来像：

So if you want to wrap the KeyCollection in a ReadOnlyCollection, you'll have to create an adapter (or wrapper) type, implementing IList<T>, wrapping the KeyCollection. So it would look like:

var dictionary = ...;
var readonly_keys = new ReadOnlyCollection<T> (new CollectionListWrapper<T> (dictionary.Keys)
);

不是很优雅，虽然，特别是作为KeyCollection已经是一个只读集合，你可以简单地传递围绕它作为一个ICollection的< T> ：）

Not very elegant though, especially as the KeyCollection is already a readonly collection, and that you could simply pass it around as an ICollection<T> :)

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