铸造一个泛型集合到基本类型 [英] Casting a generic collection to base type

问题描述

我有一个的IList＆LT; D​​erivedClass＆GT; ，我想转换为的ICollection＆LT; BaseClass的＆GT; 但是当我尝试显式转换，我得到空。是否有可能为此而不创建和填充新的集合？

I've got an IList<DerivedClass> that I want to cast to ICollection<BaseClass> but when I attempt an explicit cast, I get null. Is it possible to do this without creating and populating a new collection?

编辑： 因为我只想从集合中读取，我转而使用泛型方法：

Since I only want to read from the collection, I switched to using a generic method:

public void PopulateList<BaseClass>(ICollection<T> collection)

然后，我可以通过它的的IList＆LT; D​​erivedClass＆GT; 。有没有缓存此列表，以便我可以刷新它，当我需要一个好办法。我的第一个倾向是使用：

Then I can pass it an IList<DerivedClass>. Is there a good way to cache this list so I can refresh it when I need to. My first inclination is to use:

Object cachedCollection;
Type cachedType;
public void PopulateList<BaseClass>(ICollection<T> collection) {
    cachedCollection = collection;
    cachedType = T;

    // other stuff...
}

private void Refresh() {
    PopulateList<cachedType>(cachedCollection as ICollection<cachedType>);
}

有没有人有这样做的更好的办法？

Does anyone have a better way of doing this?

推荐答案

简短的回答是不。您将需要创建一个新的收藏与新BaseClass的类型和填充它。

The short answer is "No." You would need to create a new collection with the new BaseClass type and populate it.

如果你想想看，这是有道理的。如果你可以简单地投的集合BaseClass的，然后你可以坚持的东西，是类型BaseClass的进去，从而迫使一个简单的BaseClass对象转换为DerivedClass集合。这会破坏为目的创建具有类型安全的集合。

If you think about it, it makes sense. If you could simply "cast" your collection to BaseClass, you could then stick something that was of type "BaseClass" into it, thereby forcing a simple BaseClass object into a DerivedClass Collection. This would defeat the purpose creating a Collection with Type-Safety.

在极端情况下，如果您有两个派生类，Foo和酒吧，你可以强制酒吧对象进入美孚对象的集合按类型铸造收集回BaseClass的集合。

In the extreme case, if you had two derived classes, Foo and Bar, you could force Bar objects into a collection of Foo objects by type-casting the collection back to a collection of BaseClass.

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