C++设计模式：观察者模式_virtual void update() = 0;-优快云博客

本文介绍了一种使用C++实现的观察者模式，通过Subject和Observer类的定义，演示了如何在状态改变时通知所有观察者并更新其显示。具体包括二进制、八进制和十六进制的字符串表示。

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一、源代码：

#include<iostream>
#include<memory>
#include<vector>
#include<bitset>

using namespace std;

class Subject;
class Observer
{
public:
    virtual void update() = 0;
    virtual ~Observer() = default;
protected:
    shared_ptr<Subject> _subject;
};

class Subject
{
public:
    void notifyAllObserver()
    {
        for(const auto& observer:_observers)
        {
            observer->update();
        }
    }
    int getState()
    {
        return _state;
    }
    void setState(int state)
    {
        this->_state = state;
        notifyAllObserver();
    }
    void attach(shared_ptr<Observer> observer)
    {
        _observers.push_back(observer);
    }
private:
    vector<shared_ptr<Observer>> _observers={};
    int _state;
};

class BinaryObserver:public Observer
{
public:
    BinaryObserver(shared_ptr<Subject> subject)
    {
        this->_subject = subject;
    }
    virtual void update() override
    {
        bitset<10> b(_subject->getState());
        cout<<"  Binary String: "<<b<<endl;
    }
};

class OctalObserver:public Observer
{
public:
    OctalObserver(shared_ptr<Subject> subject)
    {
        this->_subject = subject;
    }
    virtual void update() override
    {
        cout<<"  Octal String: "<<oct<<_subject->getState()<<endl;
    }
};

class HexObserver:public Observer
{
public:
    HexObserver(shared_ptr<Subject> subject)
    {
        this->_subject = subject;
    }
    virtual void update() override
    {
        cout<<"  Hex String: "<<hex<<_subject->getState()<<endl;
    }
};

int main()
{
    shared_ptr<Subject> subject = make_shared<Subject>();
    shared_ptr<Observer> b = make_shared<BinaryObserver>(subject);
    shared_ptr<Observer> o = make_shared<OctalObserver>(subject);
    shared_ptr<Observer> h = make_shared<HexObserver>(subject);

    subject->attach(b);
    subject->attach(o);
    subject->attach(h);

    cout<<"First state change: 15"<<endl;
    subject->setState(15);
    cout<<"Second state change: 10"<<endl;
    subject->setState(10);
}

二、运行结果：