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,当对象改变时,它的依赖都会收到通知并自动更新。

 

 

// Weather.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <list>
#include <iostream>
using namespace std;

class IObserver
{
public:
	virtual void Update(float fTemp, float fHumidity, float fPressure) = 0;
};

class ISubject
{
public:
	virtual void RegisterObserver(IObserver* pObsvr) = 0;
	virtual void RemoveObserver(IObserver* pObsvr) = 0;
	virtual void NotifyObservers() = 0;
};

class IDisplayElem
{
public:
	virtual void Display() = 0;
};

class CWeatherData:public ISubject
{
public:
	CWeatherData()
	{
		m_fTemp = 0.0f;
		m_fPressure = 0.0f;
		m_fHumidity = 0.0f;
	}

	virtual ~CWeatherData()
	{
	}

public:
	//register object
	virtual void RegisterObserver(IObserver* pObsvr)
	{
		m_lsObsvr.push_back(pObsvr);
		pObsvr->Update(m_fTemp, m_fHumidity, m_fPressure);
	}

	//remove object
	virtual void RemoveObserver(IObserver* pObsvr)
	{
		LSOBSVR::iterator it;
		for (it = m_lsObsvr.begin(); it != m_lsObsvr.end(); it++)
		{
			if (*it == pObsvr)
			{
				m_lsObsvr.erase(it);
				return;
			}
		}
	}

	//notify objects
	virtual void NotifyObservers()
	{
		LSOBSVR::iterator it;
		for (it = m_lsObsvr.begin(); it != m_lsObsvr.end(); it++)
		{
			if (NULL != *it)
			{
				(*it)->Update(m_fTemp, m_fHumidity, m_fPressure);
			}
		}
	}

public:
	void MeasureChanged()
	{
		NotifyObservers();
	}

	void SetMeasurements(float fTemp, float fHumidity, float fPressure)
	{
		m_fTemp = fTemp;
		m_fPressure = fPressure;
		m_fHumidity = fHumidity;

		MeasureChanged();
	}

private:
	float	m_fTemp;
	float	m_fHumidity;
	float	m_fPressure;

	typedef list<IObserver*> LSOBSVR;
	LSOBSVR	m_lsObsvr;
};

class CCurrentConditionsDisplay:public IObserver, public IDisplayElem
{
public:
	CCurrentConditionsDisplay(ISubject* pSub)
	{
		if (NULL != pSub)
		{
			m_fTemp = 0.0f;
			m_fPressure = 0.0f;
			m_fHumidity = 0.0f;
			pSub->RegisterObserver(this);
		}
	}

	virtual ~CCurrentConditionsDisplay(){}

public:
	virtual void Update(float fTemp, float fHumidity, float fPressure)
	{
		m_fTemp = fTemp;
		m_fPressure = fPressure;
		m_fHumidity = fHumidity;

		Display();
	}

	virtual void Display()
	{
		cout << "tempteature: " << m_fTemp << "\tHumidity: " << m_fHumidity << "\tpressure:" << m_fPressure << endl;
	}

private:
	float	m_fTemp;
	float	m_fHumidity;
	float	m_fPressure;
};

int main()
{
	CWeatherData wea;
	CCurrentConditionsDisplay cc1(&wea);
	CCurrentConditionsDisplay cc2(&wea);
	CCurrentConditionsDisplay cc3(&wea);
	CCurrentConditionsDisplay cc4(&wea);
	CCurrentConditionsDisplay cc5(&wea);

	cout << "tempteature changed..." << endl;
	wea.SetMeasurements(27.0, 1.0, 2.0);

	return 0;
}