C# 中“抽象覆盖"的用途是什么? [英] What is the use of 'abstract override' in C#?

问题描述

出于好奇，我尝试覆盖基类中的抽象方法，并对实现抽象进行方法.如下:

公共抽象类 FirstAbstract{公共抽象无效 SomeMethod();}公共抽象类 SecondAbstract : FirstAbstract{公共抽象覆盖 void SomeMethod();//??这有什么意义?无论如何都没有实现会强制派生类实现抽象方法?}

想知道为什么 C# 编译器允许编写抽象覆盖".不是多余的吗?做这样的事情应该是一个编译时错误.它是否适用于某些用例?

感谢您的关注.

解决方案

Microsoft Docs - 基本上您可以强制派生类为方法提供新的实现.

公共类D{public virtual void DoWork(int i){//原始实现.}}公共抽象类 E : D{公共抽象覆盖 void DoWork(int i);}公开课 F : E{公共覆盖无效 DoWork(int i){//新的实现.}}

<块引用>

如果一个虚方法被声明为抽象的，它对任何人来说仍然是虚的从抽象类继承的类.一个类继承了一个抽象方法不能访问原始实现方法——在前面的例子中，F类上的DoWork不能调用DoWork在 D 类上.这样抽象类就可以强制派生类为虚方法提供新的方法实现.

Just out of curiosity I tried overriding a abstract method in base class, and method the implementation abstract. As below:

public abstract class FirstAbstract
{
    public abstract void SomeMethod();
}

public abstract class SecondAbstract : FirstAbstract
{
    public abstract override void SomeMethod();
    //?? what sense does this make? no implementaion would anyway force the derived classes to implement abstract method?
}

Curious to know why C# compiler allows writing 'abstract override'. Isn't it redundant? Should be a compile time error to do something like this. Does it serve to some use-case?

Thanks for your interest.

解决方案

There's a useful example for this on Microsoft Docs - basically you can force a derived class to provide a new implementation for a method.

public class D
{
    public virtual void DoWork(int i)
    {
        // Original implementation.
    }
}

public abstract class E : D
{
    public abstract override void DoWork(int i);
}

public class F : E
{
    public override void DoWork(int i)
    {
        // New implementation.
    }
}

If a virtual method is declared abstract, it is still virtual to any class inheriting from the abstract class. A class inheriting an abstract method cannot access the original implementation of the method—in the previous example, DoWork on class F cannot call DoWork on class D. In this way, an abstract class can force derived classes to provide new method implementations for virtual methods.

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