观察者模式

观察者模式定义了对象之间的一对多的依赖，这样一来，当一个对象改变状态，依赖它的对象都会收到通知，并自动更新。

       模仿书中代码、、

//观察者模式
#include <iostream>
using namespace std;
#include<vector>

class Observer;
class Subject{
public:
	virtual void registerObserver( Observer &o ){};
	virtual void removeObserver( Observer &o ){};
	virtual void notifyObserves(){};
};
class Observer{
	int id;
public:
	virtual void update(float temp, float humidity, float pressure)
	{};
	void set_id( int id )
	{
		this->id = id;
	}
	int get_id(){
		return id;
	}
};
class DisplayElement{
public:
	virtual void display(){};
};
class WeatherData:public Subject{
	vector<Observer *> observers;
	float temperature;
	float humidity;
	float pressure;
public:
	void registerObserver( Observer &o )
	{
		observers.push_back( &o );
		o.set_id( observers.size() );
	}
	void removeObserver( Observer &o )
	{
		observers.erase( observers.begin() + o.get_id() - 1 );
	}
	void notifyObservers()
	{
		for( int i = 0; i < observers.size(); ++i )
		{
			Observer *observer = observers[i];
			observer->update( temperature, humidity, pressure );
		}
	}
	void measurementsChanged()
	{
		notifyObservers();
	}
	void setMeasurements( float temperature, float humidity, float pressure )
	{
		this->temperature = temperature;
		this->humidity = humidity;
		this->pressure = pressure;
		measurementsChanged();
	}
};
class CurrentConditionsDisplay: public Observer, public DisplayElement{
	float temperature;
	float humidity;
	Subject weatherData;
public:
	CurrentConditionsDisplay( Subject &weatherData )
	{
		this->weatherData = weatherData;
		weatherData.registerObserver(*this);
	}
	virtual void update( float temperature, float humidity, float pressure )
	{
		this->temperature = temperature;
		this->humidity = humidity;
		display();
	}
	void display()
	{
		cout.setf( ios::fixed );
		cout.precision(1);
		cout<<"Current conditions: "<<temperature<<"F degrees and "<<humidity<<"% humidity"<<endl;
	}
};
void test()
{
	WeatherData *weatherData = new WeatherData();
	CurrentConditionsDisplay *currentDisplay = 
		new CurrentConditionsDisplay( *weatherData );
	weatherData->setMeasurements( 80, 65, 30.4f );
	weatherData->removeObserver( *currentDisplay );
	weatherData->setMeasurements( 82, 70, 29.2f );
	weatherData->registerObserver( *currentDisplay );
	weatherData->setMeasurements( 78, 90, 29.2f );
}
int main()
{
	test();
	return 0;
};