1）? 觀察者模式定義

略，各種設(shè)計(jì)模式的書(shū)上都有定義。

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2）? 觀察者模式一般實(shí)現(xiàn)

觀察者模式一般實(shí)現(xiàn)，都是“被觀察者”保存一個(gè)“觀察者”的列表，循環(huán)這個(gè)列表來(lái)通知“觀察者”。代碼，其中使用了boost的智能指針shared_ptr：

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[cpp]?view plaincopy

#include?<iostream>??

#include?<list>??

#include?"boost/shared_ptr.hpp"??

using?namespace?std;??

using?namespace?boost;??

??

//觀察者基類??

class?Observer??

{??

public:??

????//處理被觀察者的通知??

????virtual?void?update(const?int?i)?=?0;??

};??

??

//觀察者類A??

class?ObserverA?:?public?Observer??

{??

public:??

????virtual?void?update(const?int?i)??

????{??

????????cout?<<?"ObserverA.update("?<<?i?<<?")"?<<?endl;??

????}??

};??

??

//觀察者類B??

class?ObserverB?:?public?Observer??

{??

public:??

????virtual?void?update(const?int?i)??

????{??

????????cout?<<?"ObserverB.update("?<<?i?<<?")"?<<?endl;??

????}??

};??

??

//被觀察者基類??

class?Subject??

{??

public:??

????virtual?~Subject()??

????{??

??

????}??

????//注冊(cè)觀察者??

????virtual?void?reg(const?shared_ptr<Observer>&?pObs)?=?0;??

????//取消注冊(cè)觀察者??

????virtual?void?unreg(const?shared_ptr<Observer>&?pObs)?=?0;??

????//通知觀察者??

????virtual?void?notify(const?int?i)?=?0;??

};??

??

//被觀察者類A??

class?SubjectA?:?public?Subject??

{??

public:??

????virtual?void?reg(const?shared_ptr<Observer>&?pObs)??

????{??

????????m_lstObs.push_back(pObs);??

????}??

????virtual?void?unreg(const?shared_ptr<Observer>&?pObs)??

????{??

????????for?(list<shared_ptr<Observer>?>::iterator?it?=?m_lstObs.begin();??

????????????it?!=?m_lstObs.end();)??

????????{??

????????????if?(pObs?==?*it)?m_lstObs.erase(it++);??

????????????else?++it;??

????????}??

????}??

????virtual?void?notify(const?int?i)??

????{??

????????for?(list<shared_ptr<Observer>?>::iterator?it?=?m_lstObs.begin();??

????????????it?!=?m_lstObs.end();?++it)??

????????{??

????????????(*it)->update(i);??

????????}??

????}??

protected:??

????//觀察者類別??

????list<shared_ptr<Observer>?>?m_lstObs;??

};??

??

int?main()??

{??

????//被觀察者pSubA??

????shared_ptr<Subject>?pSubA(new?SubjectA);??

????//觀察者pObsA??

????shared_ptr<Observer>?pObsA(new?ObserverA);??

????//觀察者pObsB??

????shared_ptr<Observer>?pObsB(new?ObserverB);??

????//注冊(cè)pObsA??

????pSubA->reg(pObsA);??

????//注冊(cè)pObsB??

????pSubA->reg(pObsB);??

????//通知??

????pSubA->notify(1);????????????????//顯示??

????????????????????????????????????//ObserverA.update(1)??

????????????????????????????????????//ObserverB.update(1)??

????//取消pObsA的注冊(cè)??

????pSubA->unreg(pObsA);??

????//通知??

????pSubA->notify(2);????????????????//顯示??

????????????????????????????????????//ObserverB.update(2)??

????return?0;??

}??

?

?

3）? 觀察者模式Boost.Signals實(shí)現(xiàn)

Boost.Signals是基于函數(shù)指針或函數(shù)對(duì)象來(lái)實(shí)現(xiàn)觀察者模式的。其中Boost.Signals2是線程安全版本。代碼：

?

[cpp]?view plaincopy

#include?<iostream>??

#include?<list>??

#include?"boost/shared_ptr.hpp"??

#include?"boost/signal.hpp"??

using?namespace?std;??

using?namespace?boost;??

??

//使用函數(shù)對(duì)象來(lái)實(shí)現(xiàn)??

//觀察者類A??

class?ObserverA??

{??

public:??

????void?operator()(const?int?i)??

????{??

????????cout?<<?"ObserverA("?<<?i?<<?")"?<<?endl;??

????}??

};??

??

//觀察者類B??

class?ObserverB??

{??

public:??

????void?operator()(const?int?i)??

????{??

????????cout?<<?"ObserverB("?<<?i?<<?")"?<<?endl;??

????}??

};??

??

int?main()??

{??

????//被觀察者sig??

????signal<void?(const?int)>?sig;??

????//注冊(cè)觀察者ObserverA??

????signals::connection?connA?=?sig.connect(ObserverA());??

????//注冊(cè)觀察者ObserverB??

????sig.connect(ObserverB());??

??

????//通知??

????sig(1);?????????????????//顯示??

????????????????????????????//ObserverA(1)??

????????????????????????????//ObserverB(1)??

????//取消obsA的注冊(cè)??

????connA.disconnect();??

????//通知??

????sig(2);?????????????????//顯示??

????????????????????????????//ObserverB(2)??

????return?0;??

}??

?

Boost.Signals還支持被觀察者分組，可以對(duì)整個(gè)組進(jìn)行“通知”、取消注冊(cè)。另外，Boost.Signals需要編譯才能使用。

轉(zhuǎn)載于:https://www.cnblogs.com/lvdongjie/p/4452056.html

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