观察者模式

观察者模式 定义了对象之间的一对多依赖，这样一来，当一个对象改变时，他的所有依赖者都会收到通知并自动更新。

#include <iostream>
#include <string>
#include <vector>

using namespace std;


struct Observer {
    virtual void update() {};
};

struct Observable {
public:
    void addObserver(Observer *observer) {
        list.push_back(observer);
    }
    void deleteObserver(Observer *observer) {
        vector<Observer *>::iterator it;

        for(it=list.begin(); it!=list.end(); ++it) {
            if ((*it) == observer) {
                list.erase(it);
                break;
            }
        }
    }
    void notifyObserver() {
        vector<Observer *>::iterator it;
        for(it=list.begin(); it!=list.end(); ++it) {
            (*it)->update();
        }
    }
private:
    vector<Observer *> list;
};


struct WeatherData : public Observable {
public:
    int getTemperature() {
        return temperature;
    }

    int getHumidity() {
        return humidity;
    }

    int getPressure() {
        return pressure;
    }

    void setTemperature(int mtemperature) {
        temperature = mtemperature;
    }

    void setHumidity(int mhumidity) {
        humidity = mhumidity;
    }

    void setPressure(int mpressure) {
        pressure = mpressure;
    }

    void notifyDisplay() {
        notifyObserver();
    }
private:
    int temperature;
    int humidity;
    int pressure;
};


struct GeneralDisplay : public Observer {
public:
    GeneralDisplay(WeatherData *mweatherdata) {
        weatherdata = mweatherdata;
        weatherdata->addObserver(this);
    }

    ~GeneralDisplay() {
        weatherdata->deleteObserver(this);
    }

    virtual void update() {
        cout << "GeneralDisplay: " <<
            " Temperature: " << weatherdata->getTemperature() <<
            " Humidity: " << weatherdata->getHumidity() <<
            " Pressure: " << weatherdata->getPressure() << endl;
    }

    virtual string get_name() {
        return "GeneralDisplay";
    }

private:
    WeatherData *weatherdata;
};

struct StatisticsDisplay : public Observer {
public:
    StatisticsDisplay(WeatherData *mweatherdata) {
        weatherdata = mweatherdata;
        weatherdata->addObserver(this);
    }

    ~StatisticsDisplay() {
        weatherdata->deleteObserver(this);
    }

    virtual void update() {
        cout << "StatisticsDisplay: " <<
            " Temperature: " << weatherdata->getTemperature() <<
            " Humidity: " << weatherdata->getHumidity() <<
            " Pressure: " << weatherdata->getPressure() << endl;
    }

private:
    WeatherData *weatherdata;
};

struct ForecaseDisplay : public Observer {
public:
    ForecaseDisplay(WeatherData *mweatherdata) {
        weatherdata = mweatherdata;
        weatherdata->addObserver(this);
    }

    ~ForecaseDisplay() {
        weatherdata->deleteObserver(this);
    }

    virtual void update() {
        cout << "ForecaseDisplay: " <<
            " Temperature: " << weatherdata->getTemperature() <<
            " Humidity: " << weatherdata->getHumidity() <<
            " Pressure: " << weatherdata->getPressure() << endl;
    }

private:
    WeatherData *weatherdata;
};

int main(int argc, char **argv)
{
    WeatherData *weatherData = new WeatherData();
    GeneralDisplay *generaldisplay = new GeneralDisplay(weatherData);
    StatisticsDisplay *statisticsDisplay = new StatisticsDisplay(weatherData);
    ForecaseDisplay *forecaseDisplay = new ForecaseDisplay(weatherData);

    weatherData->setTemperature(1);
    weatherData->setHumidity(2);
    weatherData->setPressure(3);
    weatherData->notifyDisplay();

    delete forecaseDisplay;
    delete statisticsDisplay;
    delete generaldisplay;
    delete weatherData;
}