观察者模式及c++实现

转载自：http://blog.csdn.net/mafuli007/article/details/7239709

观察者模式概念：定义对象间的一种一对多的依赖关系，以便当一个对象的状态发生改变时，所有依赖于它的对象都得到通知并自动更新。“Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.” – GoF

UML图



特点：

1.观察者模式定义了对象之间一对多的关系。

2.主题（也就是可观察者）用一个共同的接口来更新观察者。

3.观察者和可观察者用松耦合的方式结合，可观察者不知道观察者的细节，只知道观察者实现了观察者接口

4.有多个观察者时，不可以依赖特点的通知次序。

C++源代码：

Observer.h

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/*

观察者模式：在对象之间定义一对多的依赖，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。

*/



#include <iostream>

#include <vector>

using namespace std;



class Observer;



//Account抽象类，用作接口

class Account

{

protected:

vector<Observer*> observer;

double balance;

public:

virtual void add_observer(Observer *o)=0;

virtual void remove_observer(Observer *o)=0;

virtual void notify_observer()=0;

virtual void set_balance(double balance)=0;

virtual double get_balance()=0;

public:

virtual ~Account()

{

cout<<"in the destructor of Account"<<endl;

}

};



//Observer抽象类，用作接口

class Observer

{

protected:

Account *account;

public:

Observer(Account *account):account(account) {}

virtual void handle_event()=0;

virtual void set_account_balance(double balance)=0;

virtual ~Observer()

{

cout<<"in the destructor of Observer"<<endl;

}

};



//BankAccount具体类，继承了ACcount抽象类

class BankAccount:public Account

{

public:



~BankAccount()

{

cout<<"in the destructor of BankAccount"<<endl;

}



public:

void add_observer(Observer *o)

{

observer.push_back(o);

}

void remove_observer(Observer *o)

{

for(vector<Observer*>::iterator it=observer.begin(); it!=observer.end(); it++)

{

if(o==*it)

{

observer.erase(it);

return;

}

}

}

void notify_observer()

{

for(vector<Observer*>::const_iterator it=observer.begin(); it!=observer.end(); it++)

{

(*it)->handle_event();

}

}

void set_balance(double balance)

{

this->balance=balance;

notify_observer();

}

double get_balance()

{

return balance;

}



};



class ATM:public Observer

{

public:

ATM(Account *account):Observer(account)//将acount传递给基类Observer的构造函数

{

}

~ATM()

{

cout<<"in the destructor of ATM"<<endl;

}

public:

void handle_event()

{

cout<<"ATM: the balance of bank accont is changed to "<<account->get_balance()<<endl;

}

void set_account_balance(double balance)

{

account->set_balance(balance);

}

};



class InternetBankService:public Observer

{

public:

InternetBankService(Account *account):Observer(account) {}

~InternetBankService()

{

cout<<"in the destructor InternetBankService "<<endl;

}

public:

void handle_event()

{

cout<<"IBS: the balance of bank account is changed to:"<<account->get_balance()<<endl;

}

void set_account_balance(double balance)

{

account->set_balance(balance);

}



};

Observer.cpp



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#include "Observer.h"

int main(int argc, char **argv)

{

Account *account=new BankAccount();

Observer *atm_observer=new ATM(account);

Observer *ibs_observer=new InternetBankService(account);



account->add_observer(atm_observer);

account->add_observer(ibs_observer);



account->set_balance(1000.12);



cout<<"Event is triggered by atm_observer"<<endl;

cout<<"============="<<endl;

atm_observer->set_account_balance(1000.23);



cout<<"Event is triggered by ibs_observer"<<endl;

cout<<"============="<<endl;

ibs_observer->set_account_balance(1000.36);



delete atm_observer;

delete ibs_observer;

return 0;

}

例2：

Test_Observer.cpp

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/*

千万要注意对象分割问题的出现。一定要理解。

*/

#include <iostream>

#include <string>

#include <vector>

using namespace std;



class Observer

{

protected:

string name;

public:

virtual void update()

{

cout<<"Observer"<<endl;

}

};



class Man:public Observer

{

public:

Man(string name)

{

this->name=name;

}

void update()

{

cout<<name<<" Man is coming"<<endl;

}

};

class Woman:public Observer

{

public:

Woman(string name)

{

this->name=name;

}

void update()

{

cout<<name<<" Woman is leaving"<<endl;

}

};



class Subject

{

private:

vector<Observer*> obser;

public:

void add(Observer &ob)

{

obser.push_back(&ob);

}

void notify()

{

for (vector<Observer*>::iterator it=obser.begin(); it!=obser.end(); it++)

{

(*it)->update();

}

}

};



int main()

{

Subject secret;

Man m1("m1--");

Man m2("m2--");

Woman w1("w1");

Woman w2("w2");



secret.add(m1);

secret.add(m2);

secret.add(w1);

secret.add(w2);



secret.notify();

return 0;



}