接口继承.没有实现接口错误 [英] Interface inheritance. Does not implement interface error

问题描述

我在使用继承接口时遇到问题.我将在下面的示例中解释我的问题.假设我有接口 IFlyable :

I have a problem with using inherited interface. I will explain my problem on example below. Let's say I have Interface IFlyable:

public interface IFlyable
{
    IVerticalSpeed Speed { get; set; }
}

它包含 IVerticalSpeed 接口.我创建了另一个名为 ISpeed 的接口，该接口继承自 IVerticalSpeed 接口:

It contains IVerticalSpeed interface. I created another interface called ISpeed which inherits from IVerticalSpeed interface:

public interface ISpeed : IVerticalSpeed
{
    int MaxSpeed { get; set; }
}

在下一步中，我创建了一个实现 IFlyable 接口的类 Fly :

In next step I created a class Fly which implement IFlyable interface:

public class Fly : IFlyable
{
    public IVerticalSpeed Speed { get; set; }
}

一切都很好...但是，如果我想将 IVerticalSpeed 接口替换为继承自 IVerticalSpeed 接口的 ISpeed 接口怎么办?

Everything is fine... but what if I wanted to replace IVerticalSpeed interface to ISpeed interface which inherits from IVerticalSpeed interface?

public class Fly : IFlyable
{
    public ISpeed Speed { get; set; }
}

我认为一切都应该没问题，因为我的 ISpeed 接口是 IVertialSpeed 接口+任何包含 ISpeed 接口的内容.但这是不对的.我收到错误消息:"Fly没有实现接口成员IFlyable.Speed(...).为什么?

I thought that everything should be fine because my ISpeed interface is IVertialSpeed interface + anything that ISpeed interface contatins. But that is not right. I get error which says: "Fly does not implement interface member IFlyable.Speed (...). Why?

推荐答案

所有答案都向您显示了可能的解决方案，但实际上没有一个答案可以回答这个重要问题:

All answers show you possible solutions but none actually answer the important question here:

我认为一切都应该没问题，因为我的 ISpeed 接口是 IVertialSpeed 接口+任何包含 ISpeed 接口的内容.但这是不对的.我收到错误消息:"Fly没有实现接口成员 IFlyable.Speed (...).为什么?

I thought that everything should be fine because my ISpeed interface is IVertialSpeed interface + anything that ISpeed interface contatins. But that is not right. I get error which says: "Fly does not implement interface member IFlyable.Speed (...). Why?

您自己说过的. ISpeed 是 IVerticalSpeed ，但并非所有 IVerticalSpeed 都是 ISpeed ，因此您根本不满足合同要求

You've said it yourself. ISpeed is an IVerticalSpeed, but not all IVerticalSpeeds are ISpeeds so you are not satisfying the contract at all.

如果您的代码被允许，而我想执行以下操作，将会发生什么事情:

What would happen if your code was allowed and I wanted to do the following:

public interface IMyOtherSpeed: IVerticalSpeed { ... }
IFlyable myFly = new Fly();
IMyOtherSpeed mySpeed = new MyOtherSpeed();

myFly.Speed = mySpeed; //Runtime error, mySpeed is not an ISpeed?!?

您现在看到问题了吗?您会违反接口的约定，因为您的类仅在应接受 any IVerticalSpeed 时接受 ISpeed .

You see the issue now? You'd be breaking the interface's contract, becuase your class only accepts ISpeed when it should accept any IVerticalSpeed.

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