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意圖：
定義對(duì)象間的一種一對(duì)多的依賴關(guān)系，當(dāng)一個(gè)對(duì)象的狀態(tài)發(fā)生變化時(shí)，所有依賴于它的對(duì)象都得到通知并被自動(dòng)更新
UML圖：

適用
當(dāng)一個(gè)抽象模型有兩個(gè)方面，其中一個(gè)方面依賴于另一方面。將這兩者封裝在獨(dú)立的對(duì)象中以使他們可以各自獨(dú)立地改變和復(fù)用
當(dāng)對(duì)一個(gè)對(duì)象的改變需要同時(shí)改變其他對(duì)象，而不知道具體有多少對(duì)象待改變
當(dāng)一個(gè)對(duì)象必須通知其他對(duì)象，而他又不能假定其他對(duì)象是誰(shuí)。換言之，你不希望這些對(duì)象是緊密耦合的

//test.h

#include <list>

typedef int STATE;

using namespace std;

//////////////////////////////////////////////////////////////////////////

class Observer;

class Subject

{

public:

Subject() : m_nSubjectState(-1){}

virtual ~Subject();

void Notify(); //通知對(duì)象改變狀態(tài)

void Attach(Observer *pObserver); //新增對(duì)象

void Detach(Observer *pObserver); //刪除對(duì)象

virtual void Setstate(STATE nState);

virtual STATE Getstate();

protected:

STATE m_nSubjectState;

list<Observer*> m_listObserver;

};

//被更新的類

class Observer

{

public:

Observer() : m_nObserverState(-1){}

virtual ~Observer(){}

virtual void Update(Subject* pSubject) = 0; //更新?tīng)顟B(tài)

protected:

STATE m_nObserverState;

};

class ConCreateSubject : public Subject

{

public:

ConCreateSubject() : Subject(){}

virtual ~ConCreateSubject(){}

virtual void SetState(STATE nState);

virtual STATE GetState();

};

class ConCreateObserver : public Observer

{

public:

ConCreateObserver() : Observer(){}

virtual ~ConCreateObserver(){}

virtual void Update(Subject* pSubject);

};

// test.cpp : Defines the entry point for the console application.

//

#include "stdafx.h"

#include <iostream>

#include <algorithm>

#include "test.h"

using namespace std;

//////////////////////////////////////////////////////////////////////////

void Subject::Attach(Observer *pObserver)

{

cout << "Attach an Observer\n";

m_listObserver.push_back(pObserver);

}

void Subject::Detach(Observer *pObserver)

{

list<Observer*>::iterator iter;

iter = find(m_listObserver.begin(),m_listObserver.end(),pObserver);

if (m_listObserver.end() != iter)

{

m_listObserver.erase(iter);

}

cout << "Detach an ObServer\n";

}

void Subject::Notify()

{

cout << "Notify Observer's state\n";

list<Observer*>::iterator iter1,iter2;

for (iter1 = m_listObserver.begin(),iter2 = m_listObserver.end(); iter1 != iter2; ++iter1)

{

(*iter1)->Update(this); //更新鏈表中所有對(duì)象的狀態(tài)

}

void Subject::Setstate(STATE nState)

{

cout << "SetState by Subject \n";

m_nSubjectState = nState;

}

STATE Subject::Getstate()

{

cout << "Getstate by Subject\n";

return m_nSubjectState;

}

Subject::~Subject()

{

list<Observer*>::iterator iter1,iter2,temp;

for (iter1 = m_listObserver.begin(),iter2 = m_listObserver.end(); iter1 != iter2;)

{

temp = iter1;

++iter1;

delete (*temp);

}

m_listObserver.clear();

}

void ConCreateSubject::SetState(STATE nState)

{

cout << "Setstate by ConCreateSubject\n";

m_nSubjectState = nState;

}

STATE ConCreateSubject::GetState()

{

cout << "Getstate by ConCreateSubject\n";

return m_nSubjectState;

}

void ConCreateObserver::Update(Subject* pSubject)

{

if (NULL == pSubject)

{

return;

}

m_nObserverState = pSubject->Getstate();

cout << "The ObserverState is" << m_nObserverState<< endl;

}

//////////////////////////////////////////////////////////////////////////

int main(int argc, char* argv[])

{

Observer *p1 = new ConCreateObserver;

Observer *p2 = new ConCreateObserver;

Subject *p = new ConCreateSubject;

p->Attach(p1);

p->Attach(p2);

p->Setstate(4);

p->Notify();

p->Detach(p1);

p->Setstate(10);

p->Notify();

delete p;

system("pause");

return 0;

}

posted on 2008-08-21 23:38 黑色天使閱讀(842) 評(píng)論(1) 編輯收藏引用所屬分類: 設(shè)計(jì)模式

FeedBack:

# re: C++設(shè)計(jì)模式-Observer

2012-05-09 15:58 | no7dw

ConCreateSubject::SetState(STATE nState);

STATE Subject::Setstate()

has a little typing error ,('S' should not a CAPical letter ) this error leads to ConCreateSubject::SetState NOT a virtual effect 回復(fù) 更多評(píng)論

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