设计模式----观察者模式 实例

代码：

#include <iostream>

#include <vector>

using namespace std;

class Account;

//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;

}

};

//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;

}

};

//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();

} //这个接口很关键

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);

}

};

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;

}

编译、运行结果：

ngnsvr9 [** NONE **]/home/xionghailong/demo/observer $ g++ main.cpp -o main

ngnsvr9 [** NONE **]/home/xionghailong/demo/observer $ ./main

ATM: the balance of bank accont is changed to 1000.12

IBS: the balance of bank account is changed to:1000.12

Event is triggered by atm_observer

=============

ATM: the balance of bank accont is changed to 1000.23

IBS: the balance of bank account is changed to:1000.23

Event is triggered by ibs_observer

=============

ATM: the balance of bank accont is changed to 1000.36

IBS: the balance of bank account is changed to:1000.36

in the destructor of ATM

in the destructor of Observer

in the destructor InternetBankService

in the destructor of Observer