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;
}
....
}
Regarding static methods used in non-generic contexts I agree that it doesn't make much sense to allow them in interfaces, since you wouldn't be able to call them if you had a reference to the interface anyway. However there is a fundamental hole in the language design created by using interfaces NOT in a polymorphic context, but in a generic one. In this case the interface is not an interface at all but rather a constraint. Because C# has no concept of a constraint outside of an interface it is missing substantial functionality. Case in point:
T SumElements<T>(T initVal, T[] values)
{
foreach (var v in values)
{
initVal += v;
}
}
这里没有多态性，泛型使用对象的实际类型并调用+=操作符，但这失败了，因为它不能确定该操作符是否存在。简单的解决方案是在约束中指定它;简单的解决方案是不可能的，因为操作符是静态的，静态方法不能在接口中，(这就是问题所在)约束被表示为接口。
c#需要的是一个真正的约束类型，所有的接口都是约束，但不是所有的约束都是接口，然后你可以这样做:
constraint CHasPlusEquals
{
static CHasPlusEquals operator + (CHasPlusEquals a, CHasPlusEquals b);
}
T SumElements<T>(T initVal, T[] values) where T : CHasPlusEquals
{
foreach (var v in values)
{
initVal += v;
}
}
已经有很多关于为所有数字类型创建i算术来实现的讨论，但是存在效率问题，因为约束不是多态构造，所以创建算术约束可以解决这个问题。
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。
