如何通过函数指针进行绑定？ [英] How to pass function pointer to bind?

问题描述

我有以下代码：

_createNewObjectlistener = eventDispatcher->addCustomEventListener(Constants::EVENT_CREATE_OBJECT, std::bind(&ObjectPlacementManager::receiveCreateObjectEvent, this, std::placeholders::_1));
_eventListeners.insert(_createNewObjectlistener);

_moveNewObjectlistener = eventDispatcher->addCustomEventListener(Constants::EVENT_MOVE_NEW_OBJECT, std::bind(&ObjectPlacementManager::receiveMoveCurrentGameObjectEvent, this, std::placeholders::_1));
_eventListeners.insert(_moveNewObjectlistener);

.... many more listeners created

每个侦听器的创建代码是 Constant :: EVENT_NAME ，并且正在调用该函数，我正在尝试将其封装为一个函数。

Since the only difference between the creation code for each listener, is the Constant::EVENT_NAME and the function being called, I am trying to encapsulate it into a function.

绑定的结果必须为const std :: function< void（EventCustom *）>&

The result of bind must be of type const std::function<void(EventCustom*)>&

像 ObjectPlacementManager :: receiveMoveCurrentGameObjectEvent 之类的函数都具有相同的签名：

The functions like ObjectPlacementManager::receiveMoveCurrentGameObjectEvent all have the same signature:

void receiveMoveCurrentGameObjectEvent(EventCustom* event){
 ....
}

我尝试了：如何将参数传递给std :: bind到函数？

typedef void (*callback_function)(EventCustom*);

EventListenerCustom* createCustomListener(callback_function func, std::string EVENT){
    auto eventDispatcher = _dragNode->getEventDispatcher();
    auto listener = eventDispatcher->addCustomEventListener(EVENT, std::bind(&func, this, std::placeholders::_1));
    _eventListeners.insert(_createNewObjectlistener);
    return listener;
}

但是我得到的错误是：

No viable conversion from '__bind<void (**)(cocos2d::EventCustom *), bejoi::ObjectPlacementManager *, const std::__1::placeholders::__ph<1> &>' to 'const std::function<void (EventCustom *)>'

我也尝试过制作一个函数：

I have also tried making a function:

EventListenerCustom* createCustomListener(void* func, std::string EVENT){
    auto eventDispatcher = _dragNode->getEventDispatcher();
    auto listener = eventDispatcher->addCustomEventListener(EVENT, std::bind(func, this, std::placeholders::_1));
    return listener;
}

但是我得到的错误是：

No viable conversion from '__bind<void *&, mynamespace:: ObjectPlacementManager *, const std::__1::placeholders::__ph<1> &>' to 'const std::function<void (EventCustom *)>'

推荐答案

第一个错误是因为您要获取函数指针的地址。因此，您要将指向函数的指针传递给 std :: bind 。

The first error is because you're taking the address of a function pointer. So you're passing a pointer to a pointer to a function to std::bind.

第二个错误是因为您使用了 void * 并以某种方式希望它能正常工作！

The second error is because you used a void * and somehow expected that to work!

尝试以下MCVE：

struct Event {};

struct Dispatcher {
  void addListener(int, const std::function<void(Event *)> &) {}
};

struct Manager {
  void receive(Event *) {}

  void addListener(int type, void (Manager::*receiver)(Event *)) {
    dis.addListener(type, std::bind(receiver, this, std::placeholders::_1));
  }

  void test() {
    addListener(42, &Manager::receive);
  }

  Dispatcher dis;
};

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