为什么c#是这样设计的?

根据我的理解,一个接口只描述行为,并且服务于描述实现接口的类的契约义务。

如果类希望在共享方法中实现这种行为,为什么不应该呢?

以下是我想到的一个例子:

// These items will be displayed in a list on the screen.
public interface IListItem {
  string ScreenName();
  ...
}

public class Animal: IListItem {
    // All animals will be called "Animal".
    public static string ScreenName() {
        return "Animal";
    }
....
}

public class Person: IListItem {

    private string name;

    // All persons will be called by their individual names.
    public string ScreenName() {
        return name;
    }

    ....

 }

当前回答

假设你在问为什么你不能这样做:

public interface IFoo {
    void Bar();
}

public class Foo: IFoo {
    public static void Bar() {}
}

This doesn't make sense to me, semantically. Methods specified on an interface should be there to specify the contract for interacting with an object. Static methods do not allow you to interact with an object - if you find yourself in the position where your implementation could be made static, you may need to ask yourself if that method really belongs in the interface. To implement your example, I would give Animal a const property, which would still allow it to be accessed from a static context, and return that value in the implementation.

public class Animal: IListItem {
    /* Can be tough to come up with a different, yet meaningful name!
     * A different casing convention, like Java has, would help here.
     */
    public const string AnimalScreenName = "Animal";
    public string ScreenName(){ return AnimalScreenName; }
}

对于更复杂的情况,您总是可以声明另一个静态方法并委托给它。在尝试给出一个例子的过程中,我想不出您在静态和实例上下文中都要做一些非平凡的事情的任何理由,因此我将给您一个FooBar blob,并将其作为它可能不是一个好主意的指示。

其他回答

接口指定对象的行为。

静态方法不指定对象的行为,而是指定以某种方式影响对象的行为。

因为接口的目的是允许多态性,能够传递任意数量的已定义类的实例,这些类都已定义,以实现已定义的接口……确保在多态调用中,代码能够找到您正在调用的方法。允许静态方法实现接口是没有意义的,

你怎么称呼它??


public interface MyInterface { void MyMethod(); }
public class MyClass: MyInterface
{
    public static void MyMethod() { //Do Something; }
}

 // inside of some other class ...  
 // How would you call the method on the interface ???
    MyClass.MyMethod();  // this calls the method normally 
                         // not through the interface...

    // This next fails you can't cast a classname to a different type... 
    // Only instances can be Cast to a different type...
    MyInterface myItf = MyClass as MyInterface;  

事实上,确实如此。

截至2022年年中,当前版本的c#完全支持所谓的静态抽象成员:

interface INumber<T>
{
    static abstract T Zero { get; }
}

struct Fraction : INumber<Fraction>
{
    public static Fraction Zero { get; } = new Fraction();

    public long Numerator;
    public ulong Denominator;

    ....
}

请注意,根据你的Visual Studio版本和你安装的。net SDK,你必须至少更新其中一个(或两个),或者你必须启用预览功能(参见在Visual Studio中使用预览功能和预览语言)。

看到更多:

https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/tutorials/static-virtual-interface-members https://blog.ndepend.com/c-11-static-abstract-members/ https://khalidabuhakmeh.com/static-abstract-members-in-csharp-10-interfaces: ~:文本=静态% 20文摘% 20成员% 20允许% 20,像% 20 % 20其他% 20接口% 20的定义。

假设你在问为什么你不能这样做:

public interface IFoo {
    void Bar();
}

public class Foo: IFoo {
    public static void Bar() {}
}

This doesn't make sense to me, semantically. Methods specified on an interface should be there to specify the contract for interacting with an object. Static methods do not allow you to interact with an object - if you find yourself in the position where your implementation could be made static, you may need to ask yourself if that method really belongs in the interface. To implement your example, I would give Animal a const property, which would still allow it to be accessed from a static context, and return that value in the implementation.

public class Animal: IListItem {
    /* Can be tough to come up with a different, yet meaningful name!
     * A different casing convention, like Java has, would help here.
     */
    public const string AnimalScreenName = "Animal";
    public string ScreenName(){ return AnimalScreenName; }
}

对于更复杂的情况,您总是可以声明另一个静态方法并委托给它。在尝试给出一个例子的过程中,我想不出您在静态和实例上下文中都要做一些非平凡的事情的任何理由,因此我将给您一个FooBar blob,并将其作为它可能不是一个好主意的指示。

因为接口是继承结构,静态方法继承不好。