在C++中实现事件(委托)(续)

在上文在C++中实现事件(委托) 中我们实现的C#里委托方式的事件处理，虽然使用很方便，但是感觉似乎少了一点C#的味道，下面我们尝试把它改成真正的C#版。

其实要改成真正的C#版，我们主要要做2件事，一是吧CEventHandler放到外面，可以让外部直接构造，二是实现operator +=和operator -=，下面是我的实现代码:

#pragma once

#include <functional>
#include <algorithm>
#include <vector>
#include <assert.h>

namespace Common
{
    typedef void* cookie_type;

    template<typename TR, typename T1, typename T2>
    class CEventHandler
    {
    public:
        typedef TR return_type;
        typedef T1 first_type;
        typedef T2 second_type;

        typedef std::function<return_type (first_type, second_type)> handler_type;

        CEventHandler(const CEventHandler& h)
        {
            _handler = h._handler;
            assert(_handler != nullptr);
        }

        CEventHandler(handler_type h)
        {
            _handler = h;
            assert(_handler != nullptr);
        }

        template<typename class_type, typename class_fun>
        CEventHandler(class_type* pThis, class_fun object_function)
        {
            using namespace std::placeholders;
            _handler = std::bind(object_function, pThis, _1, _2);
            assert(_handler != nullptr);
        }

        return_type operator()(first_type p1, second_type p2)
        {
            return_type ret = return_type();
            assert(_handler != nullptr);
            if(_handler != nullptr) ret = _handler(p1, p2);
            return ret;
        }

        handler_type _handler;
    };

    template<typename EventHandler>
    class CEvent
    {
    public:
        typedef EventHandler event_handler_type;
        typedef typename event_handler_type::return_type return_type;
        typedef typename event_handler_type::first_type first_type;
        typedef typename event_handler_type::second_type second_type;
        typedef typename event_handler_type::handler_type handler_type;

        ~CEvent()
        {
            Clear();
        }

        return_type operator()(first_type p1, second_type p2)
        {
            return_type ret = return_type();
            size_t size = _handlers.size();
            for(auto p : _handlers)
            {
                ret = p->operator()(p1, p2);
            }
            return ret;
        }

        cookie_type AddHandler(const event_handler_type& h)
        {
            event_handler_type*p = new(nothrow)  event_handler_type(h);
            if(p != nullptr) _handlers.push_back(p);
            return (cookie_type)p;
        }

        void RemoveHandler(cookie_type cookie)
        {
            event_handler_type* p = (event_handler_type*)cookie;

            auto itr = std::find(_handlers.begin(), _handlers.end(), p);
            if(itr != _handlers.end())
            {
                _handlers.erase(itr);
                delete p;
            }
            else
            {
                assert(false);
            }
        }

        cookie_type operator += (const event_handler_type& pHandler)
        {
            return AddHandler(pHandler);
        }

        void operator -= (cookie_type cookie)
        {
            RemoveHandler(cookie);
        }

        void Clear()
        {
            if(!_handlers.empty())
            {
                int n = _handlers.size();
                std::for_each(_handlers.begin(), _handlers.end(), [](event_handler_type* p)
                {
                    assert(p != nullptr);
                    delete p;
                });
                _handlers.clear();
            }
        }

    private:
        std::vector<event_handler_type*> _handlers;
    };

} //Common

然后我们就可以这样使用了:

// EventTest.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

#include <iostream>
#include "event2.h"

using namespace std;

class CObjectX
{

};

class CClickEventArgs: public CObjectX
{

};

class CButton: public CObjectX
{
public:
    void FireClick()
    {
        CClickEventArgs args;
        OnClicked(this, args);
    }

    typedef Common::CEventHandler<int, CObjectX*, CClickEventArgs&> ButtonClickEventHandler;
    Common::CEvent<ButtonClickEventHandler> OnClicked;
};

class CMyClass
{
public:
    int OnBtuttonClicked(CObjectX* pButton, CClickEventArgs& args)
    {
        cout << "CMyClass: Receive button clicked event" << endl;
        return 1;
    }
};

int OnBtuttonClicked_C_fun(CObjectX* pButton, CClickEventArgs& args)
{
    cout << "C Style Function: Receive button clicked event" << endl;
    return 1;
}

class CMyFunObj
{
public:
    int operator()(CObjectX* pButton, CClickEventArgs& args)
    {
        cout << "Functor: Receive button clicked event" << endl;
        return 1;
    }
};

int _tmain(int argc, _TCHAR* argv[])
{
    CButton btn;

    CMyClass obj;
    Common::cookie_type c1 = btn.OnClicked += CButton::ButtonClickEventHandler(&obj, &CMyClass::OnBtuttonClicked);

    Common::cookie_type c2 = btn.OnClicked += CButton::ButtonClickEventHandler(OnBtuttonClicked_C_fun);

    CMyFunObj functor;
    Common::cookie_type c3 = btn.OnClicked += CButton::ButtonClickEventHandler(functor);

    btn.FireClick();

    btn.OnClicked -= c2;

    std::cout << endl;

    btn.FireClick();

    system("pause");

    return 0;
}

怎么样，是不是感觉和C#一样了！

最后，我们比较一下2种实现方式:
第一种方法把委托函数类型封装起来了，对外部来说是透明的，使用起来更简单。
第二种方式把委托函数的类型暴露了出来，适用于事件处理函数类型各异，比较强调事件处理函数类型的场合。

其实对于C++来说，个人觉得还是第一种方式更合理，不知道大家怎么看？

注: 如果你不想用C++11的新特性或是你手头的编译器不支持C++11, 下面是一种不借助function和bind的实现方式，

直接用下面的CEventHandler替代上面的就可以了。

一种不借助C++11 function和bind的实现方式

template<typename TR, typename T1, typename T2>
    class CEventHandler
    {
    public:
        typedef TR return_type;
        typedef T1 first_type;
        typedef T2 second_type;

    private:
        class CFunctionBase
        {
        public:
            virtual return_type Invoke(first_type p1, second_type p2) = 0;
            virtual CFunctionBase* Clone() = 0;
            virtual ~CFunctionBase() { }
        };

        template<typename TFunType>
        class CFunction: public CFunctionBase
        {
        public:
            CFunction(const TFunType& f): _f(f) { }
            virtual return_type Invoke(first_type p1, second_type p2)
            {
                return _f(p1, p2);
            }
            virtual CFunctionBase* Clone()
            {
                return new CFunction(this->_f);
            }

        private:
            TFunType _f;
        };

        template<typename TClassPtr, typename TMemFunType>
        class CClassMemFun: public CFunctionBase
        {
        public:
            CClassMemFun(TClassPtr pObj, const TMemFunType& f): _pObj(pObj), _pMemFun(f) { }
            virtual return_type Invoke(first_type p1, second_type p2)
            {
                return ((*_pObj).*_pMemFun)(p1, p2);
            }
            virtual CFunctionBase* Clone()
            {
                return new CClassMemFun(this->_pObj, this->_pMemFun);
            }

        private:
            TClassPtr _pObj;
            TMemFunType _pMemFun;
        };

    public:
        template<typename TFunType>
        CEventHandler(const TFunType& f): _pFun(new CFunction<TFunType>(f)) { }

        template<typename TClassPtr, typename TMemFunType>
        CEventHandler(TClassPtr pObj, TMemFunType pFun): _pFun(new CClassMemFun<TClassPtr, TMemFunType>(pObj, pFun)) { }

        CEventHandler(const CEventHandler& f)
        {
            _pFun = f._pFun->Clone();
        }

        ~CEventHandler()
        {
            delete _pFun;
        }

        CEventHandler& operator = (const CEventHandler& f)
        {
            if(this != &f)
            {
                delete _pFun;
                _pFun = f._pFun->Clone();
            }

            return *this;
        }

        return_type operator()(first_type p1, second_type p2)
        {
            return_type ret = return_type();
            if(_pFun != nullptr)
            {
                _pFun->Invoke(p1, p2);
            }
            else
            {
                assert(false);
            }

            return ret;
        }

    private:
        CFunctionBase* _pFun;

posted on 2013-01-31 17:46 Richard Wei 阅读(2987) 评论(5) 编辑收藏举报