C＃中的接口继承 [英] Interfaces inheritance in C#

问题描述

我正在尝试在编写应用程序时遇到的问题（我）问题。
请看这个，请（为了简单起见，我会尝试缩短代码）：

I'm trying to overrun quite big (for me) problem that I came across while writing my application. Look at this, please (I will try to shorten the code for simplicity):

我有一个名为的根界面IRepository< T> ; 。
接下来， IBookRepository：IRepository< Book>
接下来，实现它的具体类： BookRepository：IBookRepository

在RepositoryManager类中，我声明了 private IRepository< IRepoItem> currentRepo;

In the RepositoryManager class I declared private IRepository<IRepoItem> currentRepo;

IRepoItem 是一个由Book类实现的接口。

IRepoItem is an interface that is implemented by Book class.

现在，当我尝试这样做时：

Now, when I try to do something like this:

currentRepo = new BookRepository();

VisualStudio提供错误消息：

VisualStudio gives error message:

无法将类型'BookRepository'隐式转换为'IRepository'。存在显式转换（您是否缺少演员？）

我试图显式转换，但抛出运行时异常...

I tried to cast explicitly, but runtime exception is thrown...

我知道（几乎可以肯定）这是一种叫做协方差的东西，这可能（可能）在.Net 4.0中解决了。
不幸的是我正在使用框架版本3.5编写，我无法改变它。请给我一些建议 - 如何超支这个问题？我想从RepoFactory获得currentRepo，它会产生几种存储库，具体取决于用户的需求。我不知道这里是否允许链接，但是我在 http://olgatherer.wordpress.com上写了一些博客。 / 我描述了应用程序创建。我的英语不好，但我希望能理解我。提前感谢您的回答。

I know (almost for sure) that it is something called covariance and this is (probably) solved in .Net 4.0. Unfortunately I'm writing using framework version 3.5, and I cannot change this. Please give me some advices what to do - how to overrun this problem? I'd like to get currentRepo from RepoFactory that would produce few kinds of repositories depends on user needs. I don't know whether links are allowed here, but I write some kind of blog on http://olgatherer.wordpress.com/ where I describe application creation. My English isn't good, but I hope that it's enough to understand me. Thank you in advance for answer.

祝你好运，
skrzeczowas

Best regards, skrzeczowas

推荐答案

在.NET 3.5中，您绝对不能将 IRepository< Book> 视为 IRepository< IRepoItem> 。

In .NET 3.5 you definitely can't treat an IRepository<Book> as an IRepository<IRepoItem>.

我们需要更多地了解您在 RepositoryManager 中使用存储库的内容真的知道如何解决它...但是你能创建一个非通用的 IRepository 接口，其中 IRepository< T> 扩展？使其包含所有不引用T的成员。然后，您可以将 currentRepo 声明为 IRepository 。

We'd need to know more about what you're using the repository for in RepositoryManager to really know how to solve it... but could you create a non-generic IRepository interface which IRepository<T> extends? Make it include all the members which don't refer to T. Then you can declare currentRepo as just an IRepository.

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