什么是C＃中使用“抽象覆盖”的？ [英] What is the use of 'abstract override' in C#?

问题描述

只是出于好奇，我试图重写在基类中的抽象方法，和方法的实施抽象。如下图所示：

 公共抽象类FirstAbstract
{
    公共抽象无效的someMethod（）;
}公共抽象类SecondAbstract：FirstAbstract
{
    公共抽象覆盖无效的someMethod（）;
    //？这确实让什么意义？没有implementaion无论如何都会迫使派生类实现抽象的方法？
}
 

想知道为什么C＃编译器允许写抽象覆盖。是不是多余的？应该是一个编译时错误做这样的事情。它是否满足某些用例？

感谢您的关注。

解决方案

有一个有用的例子，这个上的 MSDN - 基本上你可以强制派生类中提供的方法的新的实施

  D公共类
{
    公共虚拟无效的DoWork（int i）以
    {
        //原始的实现。
    }
}公共抽象E类：D
{
    公共抽象覆盖无效的DoWork（int i）以;
}公共F类：电子
{
    公共覆盖无效的DoWork（int i）以
    {
        //新的实现。
    }
}
 

  

如果一个虚拟方法声明抽象的，它仍然是虚拟的任何
  类从抽象类继承。 类的继承
  抽象方法不能访问原始实施
  方法 - 在previous例如，DoWork的对F级不能打电话的DoWork
  对D类放大器的这样，抽象类可以强制派生类
  为虚拟方法提供了新的方法实现

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 MSDN - 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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