C++中的观察者模式

目录

观察者模式（Observer Pattern）

实际应用

股票价格监控系统

发布-订阅系统

总结

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观察者模式（Observer Pattern）

观察者模式是一种行为型设计模式，它定义了对象间的一对多依赖关系。当一个对象的状态发生改变时，所有依赖于它的对象都会得到通知并自动更新。观察者模式主要包含以下角色：
1. Subject（主题）：保存对观察者的引用，并提供注册和注销观察者的方法。
2. Observer（观察者）：定义一个更新接口，用于接收主题的通知。
3. ConcreteSubject（具体主题）：具体实现主题，维护其状态并在状态改变时通知观察者。
4. ConcreteObserver（具体观察者）：具体实现观察者，响应主题的通知并进行相应的更新。

实际应用

股票价格监控系统

-- 实现一个股票价格监控系统，当股票价格发生变化时，所有注册的观察者（例如投资者）都会收到通知。

#include <iostream>
#include <vector>
#include <string>
#include <memory>// 观察者接口
class Observer {
public:virtual void update(const std::string& stockName, float price) = 0;
};// 主题接口
class Subject {
public:virtual void registerObserver(std::shared_ptr<Observer> observer) = 0;virtual void removeObserver(std::shared_ptr<Observer> observer) = 0;virtual void notifyObservers() = 0;
};// 具体主题
class Stock : public Subject {
private:std::string name;float price;std::vector<std::shared_ptr<Observer>> observers;public:Stock(const std::string& name, float price) : name(name), price(price) {}void setPrice(float newPrice) {price = newPrice;notifyObservers();}float getPrice() const {return price;}void registerObserver(std::shared_ptr<Observer> observer) override {observers.push_back(observer);}void removeObserver(std::shared_ptr<Observer> observer) override {observers.erase(std::remove(observers.begin(), observers.end(), observer), observers.end());}void notifyObservers() override {for (auto& observer : observers) {observer->update(name, price);}}
};// 具体观察者
class Investor : public Observer {
private:std::string name;public:Investor(const std::string& name) : name(name) {}void update(const std::string& stockName, float price) override {std::cout << "Investor " << name << " is notified that " << stockName << " price changed to " << price << std::endl;}
};// 客户端代码
int main() {auto stock = std::make_shared<Stock>("AAPL", 150.0);auto investor1 = std::make_shared<Investor>("Alice");auto investor2 = std::make_shared<Investor>("Bob");stock->registerObserver(investor1);stock->registerObserver(investor2);stock->setPrice(155.0);stock->setPrice(160.0);stock->removeObserver(investor1);stock->setPrice(165.0);return 0;
}

发布-订阅系统

-- 实现一个简单的发布-订阅系统，当发布者发布新消息时，所有订阅者都会收到通知。

#include <iostream>
#include <vector>
#include <string>
#include <memory>// 观察者接口
class Subscriber {
public:virtual void update(const std::string& message) = 0;
};// 主题接口
class Publisher {
public:virtual void registerSubscriber(std::shared_ptr<Subscriber> subscriber) = 0;virtual void removeSubscriber(std::shared_ptr<Subscriber> subscriber) = 0;virtual void notifySubscribers() = 0;
};// 具体主题
class NewsPublisher : public Publisher {
private:std::string latestNews;std::vector<std::shared_ptr<Subscriber>> subscribers;public:void publishNews(const std::string& news) {latestNews = news;notifySubscribers();}void registerSubscriber(std::shared_ptr<Subscriber> subscriber) override {subscribers.push_back(subscriber);}void removeSubscriber(std::shared_ptr<Subscriber> subscriber) override {subscribers.erase(std::remove(subscribers.begin(), subscribers.end(), subscriber), subscribers.end());}void notifySubscribers() override {for (auto& subscriber : subscribers) {subscriber->update(latestNews);}}
};// 具体观察者
class ConcreteSubscriber : public Subscriber {
private:std::string name;public:ConcreteSubscriber(const std::string& name) : name(name) {}void update(const std::string& message) override {std::cout << "Subscriber " << name << " received: " << message << std::endl;}
};// 客户端代码
int main() {auto publisher = std::make_shared<NewsPublisher>();auto subscriber1 = std::make_shared<ConcreteSubscriber>("Alice");auto subscriber2 = std::make_shared<ConcreteSubscriber>("Bob");publisher->registerSubscriber(subscriber1);publisher->registerSubscriber(subscriber2);publisher->publishNews("Breaking News: Observer Pattern in Action!");publisher->publishNews("Latest Update: New Design Patterns Discovered!");publisher->removeSubscriber(subscriber1);publisher->publishNews("Exclusive: Observer Pattern Simplified!");return 0;
}

总结

观察者模式帮助我们定义了对象间的一对多依赖关系，使得对象之间的通信变得更加灵活和可扩展。