C ++：Derived + Base类实现单个接口？ [英] C++: Derived + Base class implement a single interface?

问题描述

在C ++中，是否可以有一个基类加派生类实现单个接口？

In C++, is it possible to have a base plus derived class implement a single interface?

例如：

class Interface
{
    public:
        virtual void BaseFunction() = 0;
        virtual void DerivedFunction() = 0;
};

class Base
{
    public:
        virtual void BaseFunction(){}
};

class Derived : public Base, public Interface
{
    public: 
        void DerivedFunction(){}
};

void main()
{
    Derived derived;
}

此操作失败，因为Derived无法实例化。就编译器而言，Interface :: BaseFunction从未定义过。

This fails because Derived can not be instantiated. As far as the compiler is concerned Interface::BaseFunction is never defined.

到目前为止，我发现的唯一解决方案是在Derived中声明一个传递函数。 / p>

So far the only solution I've found would be to declare a pass through function in Derived

class Derived : public Base, public Interface
{
    public: 
        void DerivedFunction(){}
        void BaseFunction(){ Base::BaseFunction(); }
};

有更好的解决方案吗？

编辑：如果重要的话，这里是一个现实世界的问题，我使用MFC对话框。

If it matters, here is a real world problem I had using MFC dialogs.

我有一个对话框类（MyDialog让我们说）从CDialog派生。由于依赖问题，我需要创建一个抽象接口（MyDialogInterface）。使用MyDialogInterface的类需要使用特定于MyDialog的方法，但也需要调用CDialog :: SetParent。我只是通过创建MyDialog :: SetParent并将它传递给CDialog :: SetParent，但是想知道是否有更好的方法。

I have a dialog class (MyDialog lets say) that derives from CDialog. Due to dependency issues, I need to create an abstract interface (MyDialogInterface). The class that uses MyDialogInterface needs to use the methods specific to MyDialog, but also needs to call CDialog::SetParent. I just solved it by creating MyDialog::SetParent and having it pass through to CDialog::SetParent, but was wondering if there was a better way.

推荐答案

C ++不会注意到继承自Base的函数已经实现了 BaseFunction ：该函数必须在从 Interface 。以这种方式更改：

C++ doesn't notice the function inherited from Base already implements BaseFunction: The function has to be implemented explicitly in a class derived from Interface. Change it this way:

class Interface
{
    public:
        virtual void BaseFunction() = 0;
        virtual void DerivedFunction() = 0;
};

class Base : public Interface
{
    public:
        virtual void BaseFunction(){}
};

class Derived : public Base
{
    public: 
        virtual void DerivedFunction(){}
};

int main()
{
    Derived derived;
}

如果你只想实现其中一个， 接口分成两个接口：

If you want to be able to get away with only implementing one of them, split Interface up into two interfaces:

class DerivedInterface
{
    public:
        virtual void DerivedFunction() = 0;
};

class BaseInterface
{
    public:
        virtual void BaseFunction() = 0;
};

class Base : public BaseInterface
{
    public:
        virtual void BaseFunction(){}
};

class Derived : public DerivedInterface
{
    public: 
        virtual void DerivedFunction(){}
};  

class Both : public DerivedInterface, public Base {
    public: 
        virtual void DerivedFunction(){}
};

int main()
{
    Derived derived;
    Base base;
    Both both;
}

注意：main必须返回int

注意：好的做法是保持 virtual 在派生的成员函数前面是虚拟的基础，即使不是严格要求。

Note: main must return int
Note: it's good practise to keep virtual in front of member functions in the derived that were virtual in the base, even if it's not strictly required.

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