C++設計模式——觀察者模式

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：

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

#ifndef SUBJECT_H
#define SUBJECT_H
#include "observer.h"
class subject
{
public:
    subject();
    virtual ~subject();
    virtual void registerObserver(Observer* o) = 0;
    virtual void removeObserver(Observer* o)= 0;
    virtual void notifyObservers() = 0;
};

#endif // SUBJECT_H

#ifndef OBSERVER_H
#define OBSERVER_H

class Observer
{
public:
    Observer();
    virtual ~Observer();
    virtual void update(float temp,float humidity,float pressure) = 0;

};

#endif // OBSERVER_H

#include "weather_data.h"

WeatherData::WeatherData()
{
    m_vecObserver.clear();
}
WeatherData::~WeatherData()
{

}

void WeatherData::registerObserver(Observer *o)
{
    m_vecObserver.append(o);

}

void WeatherData::removeObserver(Observer* o)
{
  int index =  m_vecObserver.indexOf(o);
  if(index >=0)
  {
      m_vecObserver.remove(index);
  }
}

void WeatherData::notifyObservers()
{
    for(int i = 0;i < m_vecObserver.size();i++)
    {
        m_vecObserver.at(i)->update(this->temperature,this->humidity,this->pressure);
    }
}

void WeatherData::setMeasureMents(float temperature, float humidity, float pressure)
{
    this->temperature = temperature;
    this->humidity = humidity;
    this->pressure = pressure;
    measurementsChanged();
}
float WeatherData::getTemperature()
{
    return this->temperature;
}

float WeatherData::getHumidity()
{
    return this->humidity;
}

float WeatherData::getPressure()
{
    return this->pressure;
}

void WeatherData::measurementsChanged()
{
   notifyObservers();
}

#include "concreteobserver.h"
#include <QDebug>
#include <weather_data.h>
ConcreteObserver::ConcreteObserver(subject *weatherData)
{
    this->weatherData = weatherData;
    weatherData->registerObserver(this);

}

void ConcreteObserver::update(float temp, float humidity, float pressure)
{
    this->temperature = temp;
    this->humidity = humidity;
    display();
}

void ConcreteObserver::display()
{
    qDebug()<<"當前溫度："<<this->temperature<<"當前海拔："<<this->humidity;
}

#include <QCoreApplication>
#include "concreteobserver.h"
#include "weather_data.h"
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
   WeatherData* subject = new WeatherData();
    ConcreteObserver* observer = new ConcreteObserver(subject);
   subject->setMeasureMents(20,30,40);
   subject->setMeasureMents(40,50,20);


    return a.exec();
}

參考資料：HeadFirst 設計模式

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