由于这段时间较忙，自从上次我发布了一个供初学者学习的“MFC”程序后，就没怎么写文章了。这段时间在忙新的项目，项目逻辑还算复杂，用了好多有闪光点的技术，下面我要讨论的是闪光点之一：在C++中实现C#的delegate机制。
用过C#的朋友都觉得C#的确是个好语言，但有时由于特殊需要，不得不用C++，在C++中要想实现C#中的Thread等也是可行的，不过代码要稍复杂。
以例子来说明：
class Sdk
{
public:
void DoSomething();
};
class client
{
public:
Sdk m_sdk;
void DoSomething{}
{
m_sdk.DoSomething();
}
void OnMessage()
{
//
}
}
这个例子比较简单，Sdk用来实现某个功能，client是客户程序，要想在m_sdk做处理的时候能发送通知到client，有几个方法可以实现， 其一是发线程消息，其一是回调，但传统的回调对面向对象的支持并不好，这就是实现delegate的出发点。 下面是一个实现：
class Delegate
{
public:
virtual ~Delegate(void){ }
virtual void operator()(void) = 0;
};
template <typename C>
class DelegateImpl : public Delegate
{
private:
typedef void (C::*F)(void);
C* m_class;
F m_fun;
public:
DelegateImpl(C* c, F f){ m_class = c; m_fun = f; }
virtual void operator()(void)
{
if(m_class)
return (m_class-> *m_fun)();
}
};
有了上面代码，再稍加修改sdk和client代码就能实现事件通知了：
class Sdk
{
public:
Delegate* pEvent;
sdk(): pEvent(NULL) { }
void DoSomething()
{
cout < <"opened" < <endl;
if(pEvent != NULL)
(*pEvent)( );
}
};
class client
{
private:
Sdk m_sdk;
public:
client()
{
m_sdk.pEvent = new Delegate <client> (this, OnOpen);
}
void DoSomething()
{
m_sdk.DoSomething();
}
void OnDoSomething()
{
cout < <"event fired" < <endl;
}
}
上面的实现有不少局限性，事件处理方法的返回值和参数设置不是十分灵活，因此可以用宏定义优代以上代码，下面给出我的全部代码，请朋友指正。
//////////////////////////////////////////////////////////////////////////
//delegate 0
#define DEFINE_DELEGATE(NAME, R)\
class NAME##Delegate\
{\
public:\
virtual ~NAME##Delegate(void){ }\
virtual R operator()(void) = 0;\
};\
template<typename C>\
class NAME##DelegateImpl : public NAME##Delegate\
{\
private:\
typedef R (C::*F)(void);\
C* m_class;\
F m_fun;\
public:\
NAME##DelegateImpl(C* c, F f){ m_class = c; m_fun = f; }\
virtual R operator()(void)\
{\
if(m_class)\
return (m_class->*m_fun)();\
}\
};\
template<typename C, typename F>\
NAME##Delegate* Make##NAME##Delegate(C* c, F f)\
{\
return new NAME##DelegateImpl<C>(c, f);\
}
//////////////////////////////////////////////////////////////////////////
//delegate 1
#define DEFINE_DELEGATE(NAME, R, P1)\
class NAME##Delegate\
{\
public:\
virtual ~NAME##Delegate(void){ }\
virtual R operator()(P1 p1) = 0;\
};\
template<typename C>\
class NAME##DelegateImpl : public NAME##Delegate\
{\
private:\
typedef R (C::*F)(P1);\
C* m_class;\
F m_fun;\
public:\
NAME##DelegateImpl(C* c, F f){ m_class = c; m_fun = f; }\
virtual R operator()(P1 p1)\
{\
if(m_class)\
return (m_class->*m_fun)(p1);\
}\
};\
template<typename C, typename F>\
NAME##Delegate* Make##NAME##Delegate(C* c, F f)\
{\
return new NAME##DelegateImpl<C>(c, f);\
}
//////////////////////////////////////////////////////////////////////////
//delegate 2
#define DEFINE_DELEGATE(NAME, R, P1, P2)\
class NAME##Delegate\
{\
public:\
virtual ~NAME##Delegate(void){ }\
virtual R operator()(P1 p1, P2 p2) = 0;\
};\
template<typename C>\
class NAME##DelegateImpl : public NAME##Delegate\
{\
private:\
typedef R (C::*F)(P1, P2);\
C* m_class;\
F m_fun;\
public:\
NAME##DelegateImpl(C* c, F f){ m_class = c; m_fun = f; }\
virtual R operator()(P1 p1, P2 p2)\
{\
if(m_class)\
return (m_class->*m_fun)(p1, p2);\
}\
};\
template<typename C, typename F>\
NAME##Delegate* Make##NAME##Delegate(C* c, F f)\
{\
return new NAME##DelegateImpl<C>(c, f);\
}
/*
//////////////////////////////////////////////////////////////////////////
//sample
DEFINE_DELEGATE(Open, void, int, string)
class sdk
{
public:
OpenDelegate* pEvent;
sdk(): pEvent(NULL) { }
void Open()
{
cout<<"opened"<<endl;
if(pEvent != NULL)
(*pEvent)(100, "你好");
}
};
class client
{
private:
sdk m_sdk;
public:
client()
{
m_sdk.pEvent = MakeOpenDelegate(this, OnOpen2);
}
void Open()
{
m_sdk.Open();
}
void OnOpen()
{
cout<<"Open event fired"<<endl;
}
void OnOpen2(int t, string str)
{
cout<<"Open event fired, Param = "<<t<<"param2 = "<<str.c_str()<<endl;
}
};
*/
