C++中回调(CallBack)的使用方法

回调函数是一个很有用，也很重要的概念。当发生某种事件时，系统或其他函数将会 自动调用你定义的一段函数。回调函数在windows编程使用的场合很多，比如Hook回调函数：MouseProc,GetMsgProc以及 EnumWindows,DrawState的回调函数等等，还有很多系统级的回调过程。 一般情况下, 我们使用的回调函数基本都是采用C语言风格. 这里介绍一种C++风格的回调对象方法. 采用template实现.

template  <  class  Class,  typename  ReturnType,  typename  Parameter >
class  SingularCallBack
{

   public :

    typedef  ReturnType (Class::*Method)(Parameter);

    SingularCallBack(Class* _class_instance, Method _method)
    {
       //取得对象实例地址,及调用方法地址
       class_instance = _class_instance;
       method        = _method;
    };

    ReturnType operator()(Parameter parameter)
    {
       // 调用对象方法
       return  (class_instance->*method)(parameter);
    };

    ReturnType execute(Parameter parameter)
    {
       // 调用对象方法
       return  operator()(parameter);
    };


   private :

    Class*  class_instance;
    Method  method;

};

template < class Class, typename ReturnType, typename Parameter > class SingularCallBack { public: typedef ReturnType (Class::*Method)(Parameter); SingularCallBack(Class* _class_instance, Method _method) { //取得对象实例地址,及调用方法地址 class_instance = _class_instance; method = _method; }; ReturnType operator()(Parameter parameter) { // 调用对象方法 return (class_instance->*method)(parameter); }; ReturnType execute(Parameter parameter) { // 调用对象方法 return operator()(parameter); }; private: Class* class_instance; Method method; };

示例:

以下是两个类实现.

class  A
{

   public :

    void  output()
    {
       std::cout << "I am class A :D"  << std::endl;
    };

};

class  B
{

   public :

    bool  methodB(A a)
    {
       a.output();
       return   true ;
    }

};

class A { public: void output() { std::cout << "I am class A :D" << std::endl; }; }; class B { public: bool methodB(A a) { a.output(); return true; } };

SingularCallBack的各种调用示例:

A a;
B b;

SingularCallBack< B,bool ,A >* cb;
cb = new  SingularCallBack< B, bool ,A >(&b,&B::methodB);

if ((*cb)(a))
{
   std::cout << "CallBack Fired Successfully!"  << std::endl;
}
else
{
   std::cout << "CallBack Fired Unsuccessfully!"  << std::endl;
}

A a; B b; SingularCallBack< B,bool,A >* cb; cb = new SingularCallBack< B,bool,A >(&b,&B::methodB); if((*cb)(a)) { std::cout << "CallBack Fired Successfully!" << std::endl; } else { std::cout << "CallBack Fired Unsuccessfully!" << std::endl; }

A a;
B b;

SingularCallBack< B,bool ,A >* cb;
cb = new  SingularCallBack< B, bool ,A >(&b,&B::methodB);

if (cb->execute(a))
{
   std::cout << "CallBack Fired Successfully!"  << std::endl;
}
else
{
   std::cout << "CallBack Fired Unsuccessfully!"  << std::endl;
}

A a; B b; SingularCallBack< B,bool,A >* cb; cb = new SingularCallBack< B,bool,A >(&b,&B::methodB); if(cb->execute(a)) { std::cout << "CallBack Fired Successfully!" << std::endl; } else { std::cout << "CallBack Fired Unsuccessfully!" << std::endl; }

A a;
B b;
SingularCallBack< B,bool ,A >cb(&b,&B::methodB);

if (cb(a))
{
   std::cout << "CallBack Fired Successfully!"  << std::endl;
}
else
{
   std::cout << "CallBack Fired Unsuccessfully!"  << std::endl;
}

A a; B b; SingularCallBack< B,bool,A >cb(&b,&B::methodB); if(cb(a)) { std::cout << "CallBack Fired Successfully!" << std::endl; } else { std::cout << "CallBack Fired Unsuccessfully!" << std::endl; }

class  AClass
{
   public :

     AClass(unsigned int  _id): id(_id){};
    ~AClass(){};

     bool  AMethod(std::string str)
     {
        std::cout << "AClass["  << id <<  "]: "  << str << std::endl;
        return   true ;
     };

   private :

    unsigned int  id;

};


typedef  SingularCallBack < AClass,  bool , std::string > ACallBack;


int  main()
{

   std::vector < ACallBack > callback_list;

   AClass a1(1);
   AClass a2(2);
   AClass a3(3);

   callback_list.push_back(ACallBack(&a1, &AClass::AMethod));
   callback_list.push_back(ACallBack(&a2, &AClass::AMethod));
   callback_list.push_back(ACallBack(&a3, &AClass::AMethod));

   for  (unsigned  int  i = 0; i < callback_list.size(); i++)
   {
      callback_list[i]("abc" );
   }

   for  (unsigned  int  i = 0; i < callback_list.size(); i++)
   {
      callback_list[i].execute("abc" );
   }

   return   true ;

}