C++ 观察者模式样例
#include <iostream>
#include <set>
#include <string>
using namespace std;
/////////////////////抽象模式定义
class CObservable;
//观察者，纯虚基类
class CObserver
{
public:
CObserver::CObserver(){};
virtual CObserver::~CObserver(){};
//当被观察的目标发生变化时，通知调用该方法
//来自被观察者pObs, 扩展參数为pArg
virtual void Update(CObservable* pObs, void* pArg = NULL) = 0;
};
//被观察者，即Subject
class CObservable
{
public:
CObservable() : m_bChanged(false) {};
virtual ~CObservable() {};
//注冊观察者
void Attach(CObserver* pObs);
//注销观察者
void Detach(CObserver* pObs);
//注销全部观察者
void DetachAll();
//若状态变化，则遍历观察者，逐个通知更新
void Notify(void* pArg = NULL);
//測试目标状态是否变化
bool HasChanged();
//获取观察者数量
int GetObserversCount();
protected:
//设置状态变化!!!必须继承CObservable才干设置目标状态
void SetChanged();
//初始化目标为未变化状态
void ClearChanged();
private:
bool m_bChanged; //状态
set<CObserver*> m_setObs; //set保证目标唯一性
};
/////////////////////抽象模式实现
void CObservable::Attach(CObserver* pObs)
{
if (!pObs) return;
m_setObs.insert(pObs);
}
void CObservable::Detach(CObserver* pObs)
{
if (!pObs) return;
m_setObs.erase(pObs);
}
void CObservable::DetachAll()
{
m_setObs.clear();
}
void CObservable::SetChanged()
{
m_bChanged = true;
}
void CObservable::ClearChanged()
{
m_bChanged = false;
}
bool CObservable::HasChanged()
{
return m_bChanged;
}
int CObservable::GetObserversCount()
{
return m_setObs.size();
}
void CObservable::Notify(void* pArg /* = NULL */)
{
if (!HasChanged()) return;
cout << "notify observers…" << endl;
ClearChanged();
set<CObserver*>::iterator itr = m_setObs.begin();
for (; itr != m_setObs.end(); itr++)
{
(*itr)->Update(this, pArg);
}
}
/////////////////////详细应用类定义和实现
//bloger是公布者，即被观察者(subject)
class CBloger : public CObservable
{
public:
void Publish(const string &strContent)
{
cout << "bloger publish, content: " << strContent << endl;
SetChanged();
Notify(const_cast<char*>(strContent.c_str()));
}
};
//portal是公布者，即被观察者(subject)
class CPortal : public CObservable
{
public:
void Publish(const string &strContent)
{
cout << "portal publish, content: " << strContent << endl;
SetChanged();
Notify(const_cast<char*>(strContent.c_str()));
}
};
//RSS阅读器，观察者
class CRSSReader : public CObserver
{
public:
CRSSReader(const string &strName) : m_strName(strName){}
virtual void Update(CObservable* pObs, void* pArg = NULL)
{
char* pContent = static_cast<char*>(pArg);
//观察多个目标
if (dynamic_cast<CBloger*>(pObs))
{
cout << m_strName << " updated from bloger, content: " << pContent << endl;
}
else if (dynamic_cast<CPortal*>(pObs))
{
cout << m_strName << " updated from portal, content: " << pContent << endl;
}
}
private:
string m_strName;
};
//Mail阅读器，观察者
class CMailReader : public CObserver
{
public:
CMailReader(const string &strName) : m_strName(strName){}
virtual void Update(CObservable* pObs, void* pArg = NULL)
{
char* pContent = static_cast<char*>(pArg);
if (dynamic_cast<CBloger*>(pObs))
{
cout << m_strName << " updated from bloger, content: " << pContent << endl;
}
if (dynamic_cast<CPortal*>(pObs))
{
cout << m_strName << " updated from portal, content: " << pContent << endl;
}
}
private:
string m_strName;
};
/////////////////Main
int main()
{
//目标(被观察者)
CBloger* pBloger = new CBloger();
CPortal* pPortal = new CPortal();
//观察者. 一个观察者能够观察多个目标
CRSSReader* pRssReader = new CRSSReader("rss reader");
CMailReader* pMailReader = new CMailReader("mail reader");
pBloger->Attach(pRssReader); //bloger注冊观察者
pBloger->Attach(pMailReader); //bloger注冊观察者
pPortal->Attach(pRssReader); //portal注冊观察者
pPortal->Attach(pMailReader); //portal注冊观察者
//博客公布信息
pBloger->Publish("博客分享设计模式");
cout << endl;
//门户公布信息
pPortal->Publish("门户分享设计模式");
cout << "
portal detached mail reader" << endl;
pPortal->Detach(pMailReader);
cout << "portal observers count: " << pPortal->GetObserversCount() << endl << endl;
pPortal->Publish("门户分享设计模式");
system("pause");
return 0;
}