在C＃中，为什么不能一个List＆LT;字符串＆GT;对象被存储在一个列表与所述;对象＆gt;变量 [英] In C#, why can't a List<string> object be stored in a List<object> variable

问题描述

看来，一个List对象不能存储在C＃中的列表变量，甚至不能明确地投的方式。

It seems that a List object cannot be stored in a List variable in C#, and can't even be explicitly cast that way.

List<string> sl = new List<string>();
List<object> ol;
ol = sl;

结果无法隐式转换类型 System.Collections.Generic.List＆LT;字符串＆GT; 到 System.Collections.Generic.List＆LT;对象＆gt;

然后......

List<string> sl = new List<string>();
List<object> ol;
ol = (List<object>)sl;

导致无法将类型 System.Collections.Generic.List＆LT;字符串＆GT; 到 System.Collections.Generic.List＆LT;对象＆gt;

当然，你可以拉出来的一切字符串列表，并把它放回一次做到这一点，但它是一个相当复杂的解决方案。

Of course, you can do it by pulling everything out of the string list and putting it back in one at a time, but it is a rather convoluted solution.

推荐答案

想想这样说，如果你做这样的演员阵容，然后Foo类型的对象添加到列表中，字符串列表没有不再是一致的。如果你要遍历第一个参考，你会得到一类转换异常，因为一旦你打美孚情况下，富不能转换成字符串！

Think of it this way, if you were to do such a cast, and then add an object of type Foo to the list, the list of strings is no longer consistent. If you were to iterate the first reference, you would get a class cast exception because once you hit the Foo instance, the Foo could not be converted to string!

作为一个方面说明，我认为这将是更显著您是否可以做相反的转换：

As a side note, I think it would be more significant whether or not you can do the reverse cast:

List<object> ol = new List<object>();
List<string> sl;
sl = (List<string>)ol;

我还没有在一段时间使用的是C＃，所以我不知道这是否是合法的，但那种投实际上是（可能）是有用的。在这种情况下，你会从一个从一般的延伸更一般的类（对象），以更具体的类（字符串）。这样一来，如果您添加到字符串列表，你不违反对象的列表。

I haven't used C# in a while, so I don't know if that is legal, but that sort of cast is actually (potentially) useful. In this case, you are going from a more general class (object) to a more specific class (string) that extends from the general one. In this way, if you add to the list of strings, you are not violating the list of objects.

是否有人知道，也可以测试是否这样的转换是合法的，在C＃？

Does anybody know or can test if such a cast is legal in C#?

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