[行为型模式] 观察者模式的理解

墨蓝 2022-04-11 05:52 191阅读 0赞

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\[color=red\]\[b\]头文件\[/b\]\[/color\]

//ObserverPattern.h
    
    #ifndef OBSERVER_PATTERN_H
    #define OBSERVER_PATTERN_H
    
    #include <Windows.h>
    #include <iostream>
    #include <list>
    using namespace std;
    
    namespace ObserverPattern
    {
       
        class Observer
        {
       
        public:
            virtual void Update(int) = 0;
        };
    
        class Subject
        {
       
        public:
            virtual void Attach(Observer *) = 0;
            virtual void Detach(Observer *) = 0;
            virtual void Notify() = 0;
        };
    
        class ConcreteObserver : public Observer
        {
       
        public:
            ConcreteObserver(Subject *pSubject) : m_pSubject(pSubject){}
    
            void Update(int value)
            {
       
                cout<<"ConcreteObserver get the update. New State:"<<value<<endl;
            }
    
        private:
            Subject *m_pSubject;
        };
    
        class ConcreteObserver2 : public Observer
        {
       
        public:
            ConcreteObserver2(Subject *pSubject) : m_pSubject(pSubject){}
    
            void Update(int value)
            {
       
                cout<<"ConcreteObserver2 get the update. New State:"<<value<<endl;
            }
    
        private:
            Subject *m_pSubject;
        };
    
        class ConcreteSubject : public Subject
        {
       
        public:
            void Attach(Observer *pObserver);
            void Detach(Observer *pObserver);
            void Notify();
    
            void SetState(int state)
            {
       
                m_iState = state;
            }
    
        private:
            std::list<Observer *> m_ObserverList;
            int m_iState;
        };
    
        //
        void ObserverPattern_Test();
    }
    
    #endif

\[color=red\]\[b\]实现\[/b\]\[/color\]

#include "ObserverPattern.h"
    
    namespace ObserverPattern
    {
       
        void ConcreteSubject::Attach(Observer *pObserver)
        {
       
            m_ObserverList.push_back(pObserver);
        }
    
        void ConcreteSubject::Detach(Observer *pObserver)
        {
       
            m_ObserverList.remove(pObserver);
        }
    
        void ConcreteSubject::Notify()
        {
       
            std::list<Observer *>::iterator it = m_ObserverList.begin();
            while (it != m_ObserverList.end())
            {
       
                (*it)->Update(m_iState);
                ++it;
            }
        }
    
        //
        void ObserverPattern_Test()
        {
       
            // Create Subject
            ConcreteSubject *pSubject = new ConcreteSubject();
    
            // Create Observer
            Observer *pObserver = new ConcreteObserver(pSubject);
            Observer *pObserver2 = new ConcreteObserver2(pSubject);
    
            // Change the state
            pSubject->SetState(2);
    
            // Register the observer
            pSubject->Attach(pObserver);
            pSubject->Attach(pObserver2);
    
            pSubject->Notify();
    
            // Unregister the observer
            pSubject->Detach(pObserver);
    
            pSubject->SetState(3);
            pSubject->Notify();
    
            delete pObserver;
            delete pObserver2;
            delete pSubject;
        }
    }

\[color=red\]\[b\]客户端\[/b\]\[/color\]

#include "ObserverPattern.h"
    using namespace ObserverPattern;
    
    void main()
    {
       
        ObserverPattern_Test();
    }

运行结果  
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