C++設計模式——觀察者模式

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觀察者模式：定義了對象之閒的一對多依賴，這樣一來，儅一個對象改變狀態時，它的所有依賴者都會收到通知並自動更新。

觀察者模式的類圖：

代碼樣本 ：利用WeatherData對象取得數據，更新concreteobserver 並顯示出來，以下是代碼樣本：

 1 #ifndef SUBJECT_H 2 #define SUBJECT_H 3 #include "observer.h" 4 class subject 5 { 6 public: 7     subject(); 8     virtual ~subject(); 9     virtual void registerObserver(Observer* o) = 0;10     virtual void removeObserver(Observer* o)= 0;11     virtual void notifyObservers() = 0;12 };13 14 #endif // SUBJECT_H

Subject

 1 #ifndef OBSERVER_H 2 #define OBSERVER_H 3  4 class Observer 5 { 6 public: 7     Observer(); 8     virtual ~Observer(); 9     virtual void update(float temp,float humidity,float pressure) = 0;10 11 };12 13 #endif // OBSERVER_H

Observer

 1 #include "weather_data.h" 2  3 WeatherData::WeatherData() 4 { 5     m_vecObserver.clear(); 6 } 7 WeatherData::~WeatherData() 8 { 9 10 }11 12 void WeatherData::registerObserver(Observer *o)13 {14     m_vecObserver.append(o);15 16 }17 18 void WeatherData::removeObserver(Observer* o)19 {20   int index =  m_vecObserver.indexOf(o);21   if(index >=0)22   {23       m_vecObserver.remove(index);24   }25 }26 27 void WeatherData::notifyObservers()28 {29     for(int i = 0;i < m_vecObserver.size();i++)30     {31         m_vecObserver.at(i)->update(this->temperature,this->humidity,this->pressure);32     }33 }34 35 void WeatherData::setMeasureMents(float temperature, float humidity, float pressure)36 {37     this->temperature = temperature;38     this->humidity = humidity;39     this->pressure = pressure;40     measurementsChanged();41 }42 float WeatherData::getTemperature()43 {44     return this->temperature;45 }46 47 float WeatherData::getHumidity()48 {49     return this->humidity;50 }51 52 float WeatherData::getPressure()53 {54     return this->pressure;55 }56 57 void WeatherData::measurementsChanged()58 {59    notifyObservers();60 }

weather_data

 1 #include "concreteobserver.h" 2 #include <QDebug> 3 #include <weather_data.h> 4 ConcreteObserver::ConcreteObserver(subject *weatherData) 5 { 6     this->weatherData = weatherData; 7     weatherData->registerObserver(this); 8  9 }10 11 void ConcreteObserver::update(float temp, float humidity, float pressure)12 {13     this->temperature = temp;14     this->humidity = humidity;15     display();16 }17 18 void ConcreteObserver::display()19 {20     qDebug()<<"當前溫度："<<this->temperature<<"當前海拔："<<this->humidity;21 }

concreteobserver

 1 #include <QCoreApplication> 2 #include "concreteobserver.h" 3 #include "weather_data.h" 4 int main(int argc, char *argv[]) 5 { 6     QCoreApplication a(argc, argv); 7    WeatherData* subject = new WeatherData(); 8     ConcreteObserver* observer = new ConcreteObserver(subject); 9    subject->setMeasureMents(20,30,40);10    subject->setMeasureMents(40,50,20);11 12 13     return a.exec();14 }

main

參考資料：HeadFirst 設計模式

源碼：

C++設計模式——觀察者模式