C++中事件系统的原理是什么?

有很多不同的实现方式(不管是哪种语言),但抽象的想法是:

1. 有一个事件类型标识符来知道观察到的对象触发了哪些事件(可以是任何有效的事件);
2. 有一个观察者列表(或者几个,按事件类型一个?)在注册对象中注册-假设观察者是函子(函数指针或类似于函数的对象)或具有已知接口的对象(使用调用离子事件的虚拟方法);
3. 当一个事件被触发时(通过调用观察对象上的函数),我们只需浏览为事件类型注册的观察者列表,并将事件信息(id加上可能的数据)传递给要处理的观察者;

enum EventType
{
   Event_A,
   Event_B,
};

class Observer // for this example i'll suppose observer inherits this class
{
    virtual void catchEvent( EventType e ) = 0; // for sake of the example I just need the event type, not the data, but it's often required

    virtual ~Observer(){}; // virtual base classes require this to work fine.
};

class Observed
{
      typedef std::vector<Observer*> ObserverList; 
      typedef std::map< EventType, ObserverList > ObserversTable;
      ObserversTable m_observers; // we have observers for each event type

public:

     void addObserver( Observer& observer, EventType eType ) 
     { m_observers[ eType ].push_back( observer ); } // this is simplist, to say the least...

     void sendEvent( EventType event ) // here we send the event, it will be catched by observers
     { // note : often this type of system is "buffered", but here we will process it immediatly as it's a simple example

        ObserverList& observers = m_observers[ event ];  
        for ( ObserverList::iterator it = observers.begin(); it != observers.end(); ++it )
        {
              Observer* observer = *it;
              observer->catchEvent( event ); // here an observer receive the event
        }

     }
};

你看这个 excellent article 来自Pete Goodliffe,它根据所通知的事件类型路由到不同的方法。