C++ 信号2 槽回调是否可以包含 Objective-C/C++ 类/选择器（方法）信息？

Question

这对你们中的某些人来说一定很明显，但我找不到这样的例子：

我需要一个 boost::signals2 信号来连接作为 C++ 类成员函数或函子的槽回调，因此我可以将模型回调制作成 Objective-C/C++ 控制器代码。

该回调需要存储可以在 C++ 回调函数中调用的 Objective-C/C++ 方法实例的类和选择器。 （我假设没有办法实际提供 Objective-C/C++ 方法的直接回调函数地址）。我假设我需要创建一个 C++ 类/仿函数的实例来包含用于调用 Objective-C/C++ 方法的信息。

我也不确定是否可以分离出 Class 和 SEL（选择器）并将它们存储在 C++ 类的实例中以进行回调而不将它们作为 void* 传递。一旦 signal() 调用了 C++ 回调，我希望我可以使用 class_getInstanceMethod 和 method_getImplementation 将它们转换为可用（可调用）的形式。

此外，我可能希望将至少一个带有任意结构（“EventInfo”）的参数从信号发送到槽，它可以提供有关信号性质的信息。

任何人都可以照亮黑暗吗？

Answer 1

我花了很长时间，但我终于想通了。可能有更简单的方法可以做到这一点，但我发现我需要在 .mm 文件中创建一个 C++ 类，作为 boost::signals2 信号和 Objective-C 回调函数之间的桥梁：

在 CPPToCocoaModelMessageCallbacks.h 中：

/* ------------------------------------------------------------------------
    class CPPToCocoaModelMessageCallback - 
--------------------------------------------------------------------------- */
class CPPToCocoaModelMessageCallback
{
public:
    CPPToCocoaModelMessageCallback( PMD_Signal_Messenger<PrefEvent> *theSignalClass, 
                                    int         whichPrefIdxToObserve, 
                                    id          pObjCClass, 
                                    SEL         pObjCMethod);

    ~CPPToCocoaModelMessageCallback();

    void    CallBackMessage(PrefEvent* pPrefEvent);


private:

    id          fpObjCClass;
    SEL         fpObjCMethod;

    ls_index    fWhichPrefIdxToObserve;

    boost::signals2::connection fTheConnection;

};  // CPPToCocoaModelMessageCallback

在 CPPToCocoaModelMessageCallbacks.mm 中

/* ------------------------------------------------------------------------
    CPPToCocoaModelMessageCallback - CONSTRUCTOR

    whichPrefIdxToObserve - the preference idx to observe

    Pass the id and selector of the Objective-C/C++ object & method to be
    called.
--------------------------------------------------------------------------- */
CPPToCocoaModelMessageCallback::CPPToCocoaModelMessageCallback(PMD_Signal_Messenger<PrefEvent> *theSignalClass, int whichPrefIdxToObserve, id pObjCClass, SEL pObjCMethod) 
        :   fpObjCClass (pObjCClass),
            fpObjCMethod (pObjCMethod),
            fWhichPrefIdxToObserve (whichPrefIdxToObserve)
{
    fTheConnection = theSignalClass->ObserveSignal(&CPPToCocoaModelMessageCallback::CallBackMessage, this);
}

/* ------------------------------------------------------------------------
    ~CPPToCocoaModelMessageCallback - DESTRUCTOR

    Pass the id and selector of the Objective-C/C++ object & method to be
    called.
--------------------------------------------------------------------------- */
CPPToCocoaModelMessageCallback::~CPPToCocoaModelMessageCallback()
{
    fTheConnection.disconnect();
}


/* ------------------------------------------------------------------------
    CPPToCocoaModelMessageCallback::CallBackMessage - 

    Handles single and range-type preference change events.
--------------------------------------------------------------------------- */
void CPPToCocoaModelMessageCallback::CallBackMessage(PrefEvent* pPrefEvent)
{
    // Only make the callback if this event is the preference we're observing

    if (pPrefEvent->GetChangedPrefIdx() == fWhichPrefIdxToObserve) {
        [fpObjCClass performSelector:fpObjCMethod];
    }
}

/////////////////////////////////////// ////////////////////////////

在你的 controller.mm 中：

// set up messaging from Model.  The message callback functions must be destructed in dealloc.  
// I've done this in awakeFromNib but it could be elsewhere

- (void)awakeFromNib {

    PMD_Signal_Messenger<MyEventKind>* theModelClass = GetMyModelClassPointer();

    displayMenuPrefChangedCallBack = new CPPToCocoaModelMessageCallback(theModelClass, kAppPrefDictionaryDisplayShortDef, self, @selector(displayMenuChanged));
}


/* ------------------------------------------------------------------------
    displayMenuChanged - this gets called when the model fires a signal
        (via CPPToCocoaModelMessageCallback::CallBackMessage())

--------------------------------------------------------------------------- */
- (void) displayMenuChanged
{
    NSLog(@"displayMenuChanged\n");

    // DO SOMETHING TO RESPOND TO THE SIGNAL (in this case I'm reloading an NSWebView):

    [self reloadWebViewText];
}

/////////////////////////////////////// ///////////////////////////

与模型类结合用于向观察者发出信号的类：

PMD_Signal_Messenger.h：

/* ------------------------------------------------------------------------
    class PMD_Signal_Messenger<MyEventKind> -

        This class is designed to be multiple inherited with various
        Model classes.
--------------------------------------------------------------------------- */
template <class MyEventKind>
class PMD_Signal_Messenger {
public:

    PMD_Signal_Messenger() { }
    ~PMD_Signal_Messenger() { }

        template<typename Fn, typename Obj>
            boost::signals2::connection ObserveSignal(Fn callback, Obj &object) {
                return fSignalObservers.connect(boost::bind(callback, object, _1));
            }

protected:
    boost::signals2::signal<void (MyEventKind*)> fSignalObservers;  // all observers of my preference changes

private:
    PMD_Signal_Messenger(const PMD_Signal_Messenger& thePMD_Signal_Messenger)   { assert(false); }  // prevent copy constructor
};

在您要发出模型更改信号的 .cpp MODEL 文件中：

// construct theEvent (your own struct) and fire the signal with your event structure that gets passed to CPPToCocoaModelMessageCallback::CallBackMessage()

MyEventKind theEvent(someUsefulParams);

fSignalObservers(&theEvent);

Answer 2

您可以使用此解决方案： https://github.com/godexsoft/objc_callback

#pragma once
#ifndef _OBJC_CALLBACK_H_
#define _OBJC_CALLBACK_H_

template<typename Signature> class objc_callback;

template<typename R, typename... Ts>
class objc_callback<R(Ts...)>                                                              
{                              
public:                                                    
    typedef R (*func)(id, SEL, Ts...);                                              

    objc_callback(SEL sel, id obj)                  
    : sel_(sel)                                     
    , obj_(obj)                                     
    , fun_((func)[obj methodForSelector:sel])       
    {
    }     

    inline R operator ()(Ts... vs)
    {                                                   
        return fun_(obj_, sel_, vs...);      
    }                                                   
private:                                                
    SEL sel_;                                           
    id obj_;                                            
    func fun_;                                          
};      

#endif // _OBJC_CALLBACK_H_