[ZZ]C++中回调(CallBack)的使用方法

时间：2011-05-30 来源：wk23415

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;

};

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;
    }

};

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->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;
}

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;

}