由接口指定的属性的多态性-C#/.NET问题

polymorphism for properties specified by interfaces(由接口指定的属性的多态性)

本文介绍了由接口指定的属性的多态性的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

为什么这不起作用?

 public class ClassOptions {}

 public interface Inode {
    ClassOptions Options {get;}
 }            

public class MyClass : Inode {
  public ClassOptions Options { get; set; }
}           

public class ClassDerivedOptions : ClassOptions {
}

public class MyDerivedClass : Inode {
    public ClassDerivedOptions Options { get; set; } << does not implement INode...
}

[ 编译器消息告诉我为什么它会中断，但我想知道编译器为什么不让它通过的原因 - 如果有任何解决方法?- 谢谢]

[ the compiler message tells me why it breaks but i'd like to know the reasoning behind why the compiler doesnt let this through - also if there are any work arounds? - thanks]

推荐答案

它不起作用，因为 INode 接口显式调用 ClassOptions 类型的 Options 属性.C# 不支持返回类型协方差(这是您在本例中所要求的).

It doesn't work because the INode interface explicitly calls for an Options property of type ClassOptions. C# doesn't support return type covariance (which is what you're asking for in this case).

对于它的价值，Microsoft Connect 上还有一个专门针对返回类型协方差的语言功能请求:

For what it's worth, there's also a language feature request on Microsoft Connect specifically for return type covariance:

需要 C#/所有 .NET 语言中的协变返回类型

如果您查看该页面，他们还提到常见的解决方法是使用显式接口实现:

If you look at the page, they also mention that the common work-around is to use Explicit Interface Implementation:

public class MyDerivedClass : INode
{
    public ClassDerivedOptions Options { get; set; }
    public ClassOptions INode.Options { get { return Options; } }
}

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