C++中事件機制的簡潔實現及需要放棄的特性

事件模型是被廣泛使用的好東西，但是C++標准庫裡沒有現成的，其他實現又復雜或者不優雅，比如需要使用宏。現在VC11可以用在XP下了，那麼就痛快的拿起C++11提供的先進設施組合出一個輕便的實現吧。

為了達到簡潔的目的，需要放棄一些特性：
1、不支持判斷函數是否已經綁定過（因為std::function不提供比較方法，自己實現function的話代碼又變多了）
2、需要使用者接收返回的回調函數標識來移除事件綁定（原因同上）
3、事件沒有返回值，不支持回調函數優先級、條件回調等事件高級特性（比如返回所有處理結果中的最大最小值；只回調與指定參數匹配的事件處理函數）
4、事件參數理論上無限，實際上有限，一般支持0~10個參數（VC11還沒有支持變長模板參數，GCC有了。不過可以通過缺省模板參數和偏特化來模擬，所以理論上無限制）
5、不是線程安全的

注：3、5兩條可以通過引入策略模式來提供靈活支持，就像標准庫和Loki做的那樣，實現一個完整的事件機制。

最簡單的實現
代碼如下：

#include <map>
#include <functional>
using namespace std;
template<class Param1, class Param2>
class Event
{
typedef void HandlerT(Param1, Param2);
int m_handlerId;
public:
Event() : m_handlerId(0) {}
template<class FuncT> int addHandler(FuncT func)
{
m_handlers.emplace(m_handlerId, forward<FuncT>(func));
return m_handlerId++;
}
void removeHandler(int handlerId)
{
m_handlers.erase(handlerId);
}
void operator ()(Param1 arg1, Param2 arg2)
{
for ( const auto& i : m_handlers )
i.second(arg1, arg2);
}
private:
map<int, function<HandlerT>> m_handlers;
};

addHandler把回調函數完美轉發給std::function，讓標准庫來搞定各種重載，然後返回一個標識符用來注銷綁定。試一下，工作的不錯：
代碼如下：

void f1(int, int)
{
puts("f1()");
}
struct F2
{
void f(int, int)
{
puts("f2()");
}
void operator ()(int, int)
{
puts("f3()");
}
};
int _tmain(int argc, _TCHAR* argv[])
{
Event<int, int> e;
int id = e.addHandler(f1);
e.removeHandler(id);
using namespace std::placeholders;
F2 f2;
e.addHandler(bind(&F2::f, f2, _1, _2));
e.addHandler(bind(f2, _1, _2));
e.addHandler([](int, int) {
puts("f4()");
});
e(1, 2);
return 0;
}

雖然這裡有一個小小的缺點，對於仿函數，如果想使用它的指針或引用是不可以直接綁定的，需要這樣做：
代碼如下：

e.addHandler(ref(f2));
e.addHandler(ref(*pf2)); // pf2是指向f2的指針 但是使用仿函數對象指針的情形不多，也不差多敲幾個

字符，何況在有Lambda表達式的情況下呢？
改進
1、有人不喜歡bind，用起來麻煩，放到addhandler裡面去：
代碼如下：

template<class ObjT, class FuncT> int addHandler(ObjT obj, FuncT func)
{
using namespace std::placeholders;
m_handlers.emplace(m_handlerId, std::bind(func, std::forward<ObjT>(obj), _1, _2));
return m_handlerId++;
}

2、擴展參數個數。沒有變長模板參數，變通一下：
代碼如下：

struct NullType {};
template<class P1 = Private::NullType, class P2 = Private::NullType>
class Event
{
public:
template<class ObjT, class FuncT> int addHandler(ObjT obj, FuncT func)
{
using namespace std::placeholders;
m_handlers.emplace(m_handlerId, std::bind(func, std::forward<ObjT>(obj), _1, _2));
return m_handlerId++;
}
void operator ()(P1 arg1, P2 arg2)
{
for ( const auto& i : m_handlers )
i.second(arg1, arg2);
}
};
template<>
class Event<Private::NullType, Private::NullType>
{
public:
template<class ObjT, class FuncT> int addHandler(ObjT obj, FuncT func)
{
using namespace std::placeholders;
m_handlers.emplace(m_handlerId, std::bind(func, std::forward<ObjT>(obj)));
return m_handlerId++;
}
void operator ()()
{
for ( const auto& i : m_handlers )
i.second();
}
};
template<class P1>
class Event<P1, Private::NullType>
{
public:
template<class ObjT, class FuncT> int addHandler(ObjT obj, FuncT func)
{
using namespace std::placeholders;
m_handlers.emplace(m_handlerId, std::bind(func, std::forward<ObjT>(obj), _1));
return m_handlerId++;
}
void operator ()(P1 arg1)
{
for ( const auto& i : m_handlers )
i.second(arg1);
}
};

現在支持0~2個參數了。注意到各個模板裡有公共代碼，提取出來放進基類，然後要做的就是打開文本生成器了
完整代碼
代碼下載
代碼如下：

View Code
#pragma once
#include <map>
#include <functional>
namespace Utility
{
namespace Private
{
struct NullType {};
template<class HandlerT>
class EventBase
{
public:
EventBase() : m_handlerId(0) {}
template<class FuncT> int addHandler(FuncT func)
{
m_handlers.emplace(m_handlerId, std::forward<FuncT>(func));
return m_handlerId++;
}
void removeHandler(int handlerId)
{
m_handlers.erase(handlerId);
}
protected:
int m_handlerId;
std::map<int, std::function<HandlerT>> m_handlers;
};
}
template<class P1 = Private::NullType, class P2 = Private::NullType, class P3 = Private::NullType, class P4 = Private::NullType, class P5 = Private::NullType, class P6 = Private::NullType, class P7 = Private::NullType, class P8 = Private::NullType, class P9 = Private::NullType, class P10 = Private::NullType>
class Event
: public Private::EventBase<void (P1, P2, P3, P4, P5, P6, P7, P8, P9, P10)>
{
public:
using Private::EventBase<void (P1, P2, P3, P4, P5, P6, P7, P8, P9, P10)>::addHandler;
template<class ObjT, class FuncT> int addHandler(ObjT obj, FuncT func)
{
using namespace std::placeholders;
m_handlers.emplace(m_handlerId, std::bind(func, std::forward<ObjT>(obj), _1, _2, _3, _4, _5, _6, _7, _8, _9, _10));
return m_handlerId++;
}
void operator ()(P1 arg1, P2 arg2, P3 arg3, P4 arg4, P5 arg5, P6 arg6, P7 arg7, P8 arg8, P9 arg9, P10 arg10)
{
for ( const auto& i : m_handlers )
i.second(arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9, arg10);
}
};
template<>
class Event<Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType>
: public Private::EventBase<void ()>
{
public:
using Private::EventBase<void ()>::addHandler;
template<class ObjT, class FuncT> int addHandler(ObjT const obj, FuncT func)
{
m_handlers.emplace(m_handlerId, std::bind(func, obj));
return m_handlerId++;
}
void operator ()()
{
for ( const auto& i : m_handlers )
i.second();
}
};
template<class P1>
class Event<P1, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType>
: public Private::EventBase<void (P1)>
{
public:
using Private::EventBase<void (P1)>::addHandler;
template<class ObjT, class FuncT> int addHandler(ObjT obj, FuncT func)
{
using namespace std::placeholders;
m_handlers.emplace(m_handlerId, std::bind(func, std::forward<ObjT>(obj), _1));
return m_handlerId++;
}
void operator ()(P1 arg1)
{
for ( const auto& i : m_handlers )
i.second(arg1);
}
};
template<class P1, class P2>
class Event<P1, P2, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType>
: public Private::EventBase<void (P1, P2)>
{
public:
using Private::EventBase<void (P1, P2)>::addHandler;
template<class ObjT, class FuncT> int addHandler(ObjT obj, FuncT func)
{
using namespace std::placeholders;
m_handlers.emplace(m_handlerId, std::bind(func, std::forward<ObjT>(obj), _1, _2));
return m_handlerId++;
}
void operator ()(P1 arg1, P2 arg2)
{
for ( const auto& i : m_handlers )
i.second(arg1, arg2);
}
};
template<class P1, class P2, class P3>
class Event<P1, P2, P3, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType>
: public Private::EventBase<void (P1, P2, P3)>
{
public:
using Private::EventBase<void (P1, P2, P3)>::addHandler;
template<class ObjT, class FuncT> int addHandler(ObjT obj, FuncT func)
{
using namespace std::placeholders;
m_handlers.emplace(m_handlerId, std::bind(func, std::forward<ObjT>(obj), _1, _2, _3));
return m_handlerId++;
}
void operator ()(P1 arg1, P2 arg2, P3 arg3)
{
for ( const auto& i : m_handlers )
i.second(arg1, arg2, arg3);
}
};
template<class P1, class P2, class P3, class P4>
class Event<P1, P2, P3, P4, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType>
: public Private::EventBase<void (P1, P2, P3, P4)>
{
public:
using Private::EventBase<void (P1, P2, P3, P4)>::addHandler;
template<class ObjT, class FuncT> int addHandler(ObjT obj, FuncT func)
{
using namespace std::placeholders;
m_handlers.emplace(m_handlerId, std::bind(func, std::forward<ObjT>(obj), _1, _2, _3, _4));
return m_handlerId++;
}
void operator ()(P1 arg1, P2 arg2, P3 arg3, P4 arg4)
{
for ( const auto& i : m_handlers )
i.second(arg1, arg2, arg3, arg4);
}
};
template<class P1, class P2, class P3, class P4, class P5>
class Event<P1, P2, P3, P4, P5, Private::NullType, Private::NullType, Private::NullType, Private::NullType, Private::NullType>
: public Private::EventBase<void (P1, P2, P3, P4, P5)>
{
public:
using Private::EventBase<void (P1, P2, P3, P4, P5)>::addHandler;
template<class ObjT, class FuncT> int addHandler(ObjT obj, FuncT func)
{
using namespace std::placeholders;
m_handlers.emplace(m_handlerId, std::bind(func, std::forward<ObjT>(obj), _1, _2, _3, _4, _5));
return m_handlerId++;
}
void operator ()(P1 arg1, P2 arg2, P3 arg3, P4 arg4, P5 arg5)
{
for ( const auto& i : m_handlers )
i.second(arg1, arg2, arg3, arg4, arg5);
}
};
template<class P1, class P2, class P3, class P4, class P5, class P6>
class Event<P1, P2, P3, P4, P5, P6, Private::NullType, Private::NullType, Private::NullType, Private::NullType>
: public Private::EventBase<void (P1, P2, P3, P4, P5, P6)>
{
public:
using Private::EventBase<void (P1, P2, P3, P4, P5, P6)>::addHandler;
template<class ObjT, class FuncT> int addHandler(ObjT obj, FuncT func)
{
using namespace std::placeholders;
m_handlers.emplace(m_handlerId, std::bind(func, std::forward<ObjT>(obj), _1, _2, _3, _4, _5, _6));
return m_handlerId++;
}
void operator ()(P1 arg1, P2 arg2, P3 arg3, P4 arg4, P5 arg5, P6 arg6)
{
for ( const auto& i : m_handlers )
i.second(arg1, arg2, arg3, arg4, arg5, arg6);
}
};
template<class P1, class P2, class P3, class P4, class P5, class P6, class P7>
class Event<P1, P2, P3, P4, P5, P6, P7, Private::NullType, Private::NullType, Private::NullType>
: public Private::EventBase<void (P1, P2, P3, P4, P5, P6, P7)>
{
public:
using Private::EventBase<void (P1, P2, P3, P4, P5, P6, P7)>::addHandler;
template<class ObjT, class FuncT> int addHandler(ObjT obj, FuncT func)
{
using namespace std::placeholders;
m_handlers.emplace(m_handlerId, std::bind(func, std::forward<ObjT>(obj), _1, _2, _3, _4, _5, _6, _7));
return m_handlerId++;
}
void operator ()(P1 arg1, P2 arg2, P3 arg3, P4 arg4, P5 arg5, P6 arg6, P7 arg7)
{
for ( const auto& i : m_handlers )
i.second(arg1, arg2, arg3, arg4, arg5, arg6, arg7);
}
};
template<class P1, class P2, class P3, class P4, class P5, class P6, class P7, class P8>
class Event<P1, P2, P3, P4, P5, P6, P7, P8, Private::NullType, Private::NullType>
: public Private::EventBase<void (P1, P2, P3, P4, P5, P6, P7, P8)>
{
public:
using Private::EventBase<void (P1, P2, P3, P4, P5, P6, P7, P8)>::addHandler;
template<class ObjT, class FuncT> int addHandler(ObjT obj, FuncT func)
{
using namespace std::placeholders;
m_handlers.emplace(m_handlerId, std::bind(func, std::forward<ObjT>(obj), _1, _2, _3, _4, _5, _6, _7, _8));
return m_handlerId++;
}
void operator ()(P1 arg1, P2 arg2, P3 arg3, P4 arg4, P5 arg5, P6 arg6, P7 arg7, P8 arg8)
{
for ( const auto& i : m_handlers )
i.second(arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8);
}
};
template<class P1, class P2, class P3, class P4, class P5, class P6, class P7, class P8, class P9>
class Event<P1, P2, P3, P4, P5, P6, P7, P8, P9, Private::NullType>
: public Private::EventBase<void (P1, P2, P3, P4, P5, P6, P7, P8, P9)>
{
public:
using Private::EventBase<void (P1, P2, P3, P4, P5, P6, P7, P8, P9)>::addHandler;
template<class ObjT, class FuncT> int addHandler(ObjT obj, FuncT func)
{
using namespace std::placeholders;
m_handlers.emplace(m_handlerId, std::bind(func, std::forward<ObjT>(obj), _1, _2, _3, _4, _5, _6, _7, _8, _9));
return m_handlerId++;
}
void operator ()(P1 arg1, P2 arg2, P3 arg3, P4 arg4, P5 arg5, P6 arg6, P7 arg7, P8 arg8, P9 arg9)
{
for ( const auto& i : m_handlers )
i.second(arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9);
}
};
} // namespace Utility

測試代碼
各種綁定方式
代碼如下：

View Code
#include "Event.h"
using namespace std;
void f1(int, int)
{
puts("f1()");
}
struct F2
{
F2() { puts("F2 construct"); }
F2(const F2 &) { puts("F2 copy"); }
F2(F2 &&) { puts("F2 move"); }
F2& operator=(const F2 &) { puts("F2 copy assign"); return *this; }
F2& operator=(F2 &&) { puts("F2 move assign"); return *this; }
void f(int, int)
{
puts("f2()");
}
void fc(int, int) const
{
puts("f2c()");
}
};
struct F3
{
F3() { puts("F3 construct"); }
F3(const F3 &) { puts("F3 copy"); }
F3(F3 &&) { puts("F3 move"); }
F3& operator=(const F3 &) { puts("F3 copy assign"); return *this; }
F3& operator=(F3 &&) { puts("F3 move assign"); return *this; }
void operator ()(int, int) const
{
puts("f3()");
}
};
int _tmain(int argc, _TCHAR* argv[])
{
Utility::Event<int, int> e;
// 一般函數
e.addHandler(f1);
int id = e.addHandler(&f1);
e.removeHandler(id); // 移除事件處理函數
// 成員函數
using namespace std::placeholders;
F2 f2;
const F2 *pf2 = &f2;
e.addHandler(bind(&F2::f, &f2, _1, _2)); // std::bind
e.addHandler(&f2, &F2::f);
e.addHandler(pf2, &F2::fc); // 常量指針
puts("----addHandler(f2, &F2::f)----");
e.addHandler(f2, &F2::f); // 對象拷貝構造
puts("----addHandler(F2(), &F2::f)----");
e.addHandler(F2(), &F2::f); // 對象轉移構造
puts("--------");
// 仿函數
F3 f3;
const F3 *pf3 = &f3;
puts("----addHandler(f3)----");
e.addHandler(f3); // 對象拷貝構造
puts("----addHandler(F3())----");
e.addHandler(F3()); // 對象轉移構造
puts("--------");
e.addHandler(ref(f3)); // 引用仿函數對象
e.addHandler(ref(*pf3)); // 引用仿函數常量對象
puts("--------");
// Lambda表達式
e.addHandler([](int, int) {
puts("f4()");
});
// 激發事件
e(1, 2);
return 0;
}