在此種模式中，一個(gè)目標(biāo)對(duì)象管理所有相依于它的觀(guān)察者對(duì)象，并且在它本身的狀態(tài)改變時(shí)主動(dòng)發(fā)出通知。這通常透過(guò)呼叫各觀(guān)察者所提供的方法來(lái)實(shí)現(xiàn)。此種模式通常被用來(lái)實(shí)作事件處理系統(tǒng)。

 通俗點(diǎn)來(lái)說(shuō)，就是一個(gè)主題類(lèi)(subject)在狀態(tài)發(fā)生改變時(shí)，通過(guò)觀(guān)察者(observer)提供的方法，來(lái)更新觀(guān)察者的狀態(tài)。首先觀(guān)察者需要到主題類(lèi)中注冊(cè)。

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附帶維基百科的代碼：

python:相對(duì)簡(jiǎn)潔

class AbstractSubject(object):
    def register(self, listener):
        raise NotImplementedError("Must subclass me")
 
    def unregister(self, listener):
        raise NotImplementedError("Must subclass me")
 
    def notify_listeners(self,event):
        raise NotImplementedError("Must subclass me")
 
class Listener(object):
    def __init__(self, name, subject):
        self.name= name
        subject.register(self)
 
    def notify(self,event):
        print self.name,"received event", event 
class Subject(AbstractSubject):
    def __init__(self):
        self.listeners= []
        self.data= None
 
    def getUserAction(self):
        self.data= raw_input('Enter something to do:')
return self.data
 
    # Implementabstract Class AbstractSubject
 
    def register(self, listener):
        self.listeners.append(listener)
 
    def unregister(self, listener):
        self.listeners.remove(listener)
 
    def notify_listeners(self,event):
for listener in self.listeners:
            listener.notify(event)
 
 
if __name__=="__main__":
    # make a subjectobject to spy on
    subject= Subject()
 
    # register two listeners to monitor it.
    listenerA= Listener("", subject)
    listenerB= Listener("", subject)
 
    # simulatedevent
    subject.notify_listeners ("")
    # outputs:
    # received event 
    # received event 
 
    action= subject.getUserAction()
    subject.notify_listeners(action)
    #Enter something todo:hello
    # outputs:
    # received event hello
    # received event hello

C++代碼，需要多理解：

#include 
#include
#include
#include
using namespace std;
 
// The Abstract Observerclass ObserverBoardInterface
{
public:
virtual void update(float a,float b,float c) = 0;
};
 
// Abstract Interface for Displaysclass DisplayBoardInterface
{
public:
virtual void show() = 0;
};
 
// The Abstract Subjectclass WeatherDataInterface
{
public:
virtual void registerob(ObserverBoardInterface* ob) = 0;
virtual void removeob(ObserverBoardInterface* ob) = 0;
virtual void notifyOb() = 0;
};
 
// The Concrete Subjectclass ParaWeatherData: public WeatherDataInterface
{
public:
void SensorDataChange(float a,float b,float c)
    {
        m_humidity= a;
        m_temperature= b;
        m_pressure= c;
        notifyOb();
    }
 
void registerob(ObserverBoardInterface* ob)
    {
        m_obs.push_back(ob);
    }
 
void removeob(ObserverBoardInterface* ob)
    {
        m_obs.remove(ob);
    }
protected:
void notifyOb()
    {
        list::iterator pos = m_obs.begin();
while (pos != m_obs.end())
        {
            ((ObserverBoardInterface* )(*pos))->update(m_humidity,m_temperature,m_pressure);
            (dynamic_cast(*pos))->show();
++pos;
        }
    }
 
private:
float        m_humidity;
float        m_temperature;
float        m_pressure;
    list m_obs;
};
 
// A Concrete Observerclass CurrentConditionBoard : public ObserverBoardInterface, public DisplayBoardInterface
{
public:
    CurrentConditionBoard(WeatherDataInterface& a):m_data(a)
    {
        m_data.registerob(this);
    }
void show()
    {
        cout<<"_____CurrentConditionBoard_____"<m_maxt)
        {
            m_maxt= t;
        }
if (tSensorDataChange(10.2, 28.2, 1001);
    wdata->SensorDataChange(12, 30.12, 1003);
    wdata->SensorDataChange(10.2, 26, 806);
    wdata->SensorDataChange(10.3, 35.9, 900);
 
    wdata->removeob(currentB);
 
    wdata->SensorDataChange(100, 40, 1900);  
 
    delete statisticB;
    delete currentB;
    delete wdata;
 
return 0;
}

當(dāng)前標(biāo)題：設(shè)計(jì)模式（二）：觀(guān)察者模式-創(chuàng)新互聯(lián)
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