我真的不明白接口存在的原因。据我所知，这是c#中不存在的多继承的一种工作(至少我是这么被告知的)。
我所看到的是，您预定义了一些成员和函数，然后必须在类中再次重新定义它们。从而使接口成为冗余。它只是感觉像句法……嗯，垃圾对我来说(请没有冒犯的意思。Junk是指无用的东西)。
在下面的例子中，我将创建一个名为Pizza的基类，而不是一个接口。
简单示例(取自不同的堆栈溢出贡献)
public interface IPizza
{
public void Order();
}
public class PepperoniPizza : IPizza
{
public void Order()
{
//Order Pepperoni pizza
}
}
public class HawaiiPizza : IPizza
{
public void Order()
{
//Order HawaiiPizza
}
}
当前回答
接口定义了某种功能的提供者和相应的使用者之间的契约。它将实现与契约(接口)解耦。您应该了解一下面向对象的体系结构和设计。你可能想从维基百科开始:http://en.wikipedia.org/wiki/Interface_(computing)
其他回答
考虑到你不能在c#中使用多重继承，然后再看看你的问题。
关键是接口代表一个契约。任何实现类都必须拥有的一组公共方法。从技术上讲，接口只控制语法，即有什么方法，它们得到什么参数以及它们返回什么。通常它们也封装语义，尽管只是通过文档。
然后，您可以拥有一个接口的不同实现，并随意交换它们。在您的示例中，由于每个披萨实例都是IPizza，因此在处理未知披萨类型实例的任何地方都可以使用IPizza。任何类型继承自IPizza的实例都保证是可排序的，因为它有一个Order()方法。
Python is not statically-typed, therefore types are kept and looked up at runtime. So you can try calling an Order() method on any object. The runtime is happy as long as the object has such a method and probably just shrugs and says »Meh.« if it doesn't. Not so in C#. The compiler is responsible for making the correct calls and if it just has some random object the compiler doesn't know yet whether the instance during runtime will have that method. From the compiler's point of view it's invalid since it cannot verify it. (You can do such things with reflection or the dynamic keyword, but that's going a bit far right now, I guess.)
还要注意，通常意义上的接口不一定是c#接口，它也可以是一个抽象类，甚至是一个普通类(如果所有子类都需要共享一些公共代码，这可以派上用场——然而，在大多数情况下，接口就足够了)。
接口用于应用不同类之间的连接。例如，你有一个关于汽车和树的类;
public class Car { ... }
public class Tree { ... }
您希望为这两个类添加一个可燃功能。但是每个职业都有自己的燃烧方式。所以你只要做;
public class Car : IBurnable
{
public void Burn() { ... }
}
public class Tree : IBurnable
{
public void Burn() { ... }
}
I share your sense that Interfaces are not necessary. Here is a quote from Cwalina pg 80 Framework Design Guidelines "I often here people saying that interfaces specify contracts. I believe this a dangerous myth. Interfaces by themselves do not specify much. ..." He and co-author Abrams managed 3 releases of .Net for Microsoft. He goes on to say that the 'contract' is "expressed" in an implementation of the class. IMHO watching this for decades, there were many people warning Microsoft that taking the engineering paradigm to the max in OLE/COM might seem good but its usefulness is more directly to hardware. Especially in a big way in the 80s and 90s getting interoperating standards codified. In our TCP/IP Internet world there is little appreciation of the hardware and software gymnastics we would jump through to get solutions 'wired up' between and among mainframes, minicomputers, and microprocessors of which PCs were just a small minority. So coding to interfaces and their protocols made computing work. And interfaces ruled. But what does solving making X.25 work with your application have in common with posting recipes for the holidays? I have been coding C++ and C# for many years and I never created one once.
这里有很多很好的答案，但我想从一个稍微不同的角度来尝试。
你可能熟悉面向对象设计的SOLID原则。总而言之:
S -单一责任原则 O -开/闭原则 利斯科夫替换原理 I -界面隔离原理 D -依赖倒置原理
遵循SOLID原则有助于生成干净、分解良好、内聚和松散耦合的代码。考虑到:
用法与例句:“依赖管理是软件在任何规模上的主要挑战”(唐纳德·克努特)
那么任何有助于依赖管理的东西都是一个巨大的胜利。接口和依赖倒置原则确实有助于将代码与具体类的依赖解耦，因此可以根据行为而不是实现来编写和推理代码。这有助于将代码分解成可以在运行时而不是编译时组合的组件，也意味着这些组件可以很容易地插入和取出，而无需更改其余代码。
Interfaces help in particular with the Dependency Inversion Principle, where code can be componentized into a collection of services, with each service being described by an interface. Services can then be "injected" into classes at runtime by passing them in as a constructor parameter. This technique really becomes critical if you start to write unit tests and use test driven development. Try it! You will quickly understand how interfaces help to break apart the code into manageable chunks that can be individually tested in isolation.
