如何实现虚函数回调？

发布于 2025-01-08 01:32:35 字数 394 浏览 1 评论 0原文

我正在使用 wxWigets，但我想这个问题更多的是如何实现虚函数回调。这是我的代码的（非常）简化版本：

// MyGUI.h 
Class MyGUI : public wxFrame {

  ...
  protected:
     virtual void onFeedButton_cb( wxCommandEvent& event ) { event.Skip(); }
  ...
}

// Animal.h 
Class Animal {

  public: 
       void Feed(); 
}

一个简单的问题：如何实现 onFeedButton_cb 回调，以便它可以访问 Animal 的 Feed() 函数？即在运行时回调必须能够访问 Animal 的实例。

原文

I am using wxWigets, but I suppose this question is more of how to implement callbacks that are virtual functions. This is a (very) simplified version of my code:

// MyGUI.h 
Class MyGUI : public wxFrame {

  ...
  protected:
     virtual void onFeedButton_cb( wxCommandEvent& event ) { event.Skip(); }
  ...
}

// Animal.h 
Class Animal {

  public: 
       void Feed(); 
}

A trivial question: How do I implement the onFeedButton_cb callback so that it can access Animal's Feed() function?? i.e. during run time the callback must have access to an instance of Animal.

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女皇必胜 2025-01-15 01:32:35

定义一个为您调用该虚拟函数的非虚拟函数，并将该非虚拟函数附加到回调中。

#include <memory>
#include <iostream>

class Animal { virtual void Roar() { std::cout << "Roar!\n"; } };
class Rabbit : public class Animal { virtual void Roar() {
    std::cout << "Rabbits don't roar, silly!\n"; } };

typedef void (*NonVirtualCallbackType)(Animal *);

void Callback(Animal *foo)
{
    //Virtual call happens inside the callback
    foo->Roar();
}

void FunctionUsingCallback(NonVirtualCallbackType callback, Animal *instance)
{
    callback(instance);
}

int main()
{
    std::unique_ptr<Animal> generals(new Animal());
    std::unique_ptr<Animal> wabbits(new Rabbit());
    FunctionUsingCallback(Callback, generals);
    FunctionUsingCallback(Callback, wabbits);
}

请注意，这种转换正是 std::mem_fun 在 STL 函子的幕后所做的事情，尽管它依赖于编译时而不是运行时多态性。

Define a non-virtual function that calls the virtual function for you, and attach the non-virtual function to the callback.

#include <memory>
#include <iostream>

class Animal { virtual void Roar() { std::cout << "Roar!\n"; } };
class Rabbit : public class Animal { virtual void Roar() {
    std::cout << "Rabbits don't roar, silly!\n"; } };

typedef void (*NonVirtualCallbackType)(Animal *);

void Callback(Animal *foo)
{
    //Virtual call happens inside the callback
    foo->Roar();
}

void FunctionUsingCallback(NonVirtualCallbackType callback, Animal *instance)
{
    callback(instance);
}

int main()
{
    std::unique_ptr<Animal> generals(new Animal());
    std::unique_ptr<Animal> wabbits(new Rabbit());
    FunctionUsingCallback(Callback, generals);
    FunctionUsingCallback(Callback, wabbits);
}

Note that this kind of conversion is exactly what std::mem_fun does under the covers for STL functors, though it relies on compile time rather than runtime polymorphism.

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美男兮 2025-01-15 01:32:35

鉴于您评论中的解释，似乎您需要：

使 MyGUI.h 中的代码了解 Animal
为指向唯一 Animal 实例的指针定义

也许类似this：

// MyGUI.h 
#include "Animal.h"

Class MyGUI : public wxFrame {

  ...
  protected:
     virtual void onFeedButton_cb( wxCommandEvent& event ) {
        Animal::getTheAnimal()->Feed();
        event.Skip(); }
  ...
}

// Animal.h 
Class Animal {
  private:
       static Animal* theAnimal;

  public:
       static Animal& getTheAnimal() { return *theAnimal; }

  public:
       Animal() { theAnimal = this; }

  public: 
       void Feed(); 
}

另请参阅 Singleton 模式。

Given the explanations in your comments, it seems you need to:

make the code in MyGUI.h aware of Animal
define a global storage for a pointer to the only Animal instance

Perhaps something like this:

// MyGUI.h 
#include "Animal.h"

Class MyGUI : public wxFrame {

  ...
  protected:
     virtual void onFeedButton_cb( wxCommandEvent& event ) {
        Animal::getTheAnimal()->Feed();
        event.Skip(); }
  ...
}

// Animal.h 
Class Animal {
  private:
       static Animal* theAnimal;

  public:
       static Animal& getTheAnimal() { return *theAnimal; }

  public:
       Animal() { theAnimal = this; }

  public: 
       void Feed(); 
}