观察者模式（Observer Pattern）
#include <iostream>
#include <vector>
#include <unordered_map>
#include <list>
// 抽象观察者
class Observer {
public:
virtual void handleMessage(int messageID) = 0;
virtual ~Observer() = default;
};
// 具体观察者1：观察者感兴趣的是消息 1 和 2
class Observer1 : public Observer {
public:
void handleMessage(int messageID) override {
if (messageID == 1 || messageID == 2) {
std::cout << "Observer1 received message: " << messageID << std::endl;
} else {
std::cout << "Observer1 ignored message: " << messageID << std::endl;
}
}
};
// 具体观察者2：观察者感兴趣的是消息 2
class Observer2 : public Observer {
public:
void handleMessage(int messageID) override {
if (messageID == 2) {
std::cout << "Observer2 received message: " << messageID << std::endl;
} else {
std::cout << "Observer2 ignored message: " << messageID << std::endl;
}
}
};
// 具体观察者3：观察者感兴趣的是消息 1 和 3
class Observer3 : public Observer {
public:
void handleMessage(int messageID) override {
if (messageID == 1 || messageID == 3) {
std::cout << "Observer3 received message: " << messageID << std::endl;
} else {
std::cout << "Observer3 ignored message: " << messageID << std::endl;
}
}
};
// 主题类
class Subject {
private:
// 维护消息ID到观察者列表的映射
std::unordered_map<int, std::list<Observer*>> observers;
public:
// 添加观察者
void addObserver(int messageID, Observer* observer) {
observers[messageID].push_back(observer);
}
// 通知观察者
void notifyObservers(int messageID) {
if (observers.find(messageID) != observers.end()) {
for (Observer* observer : observers[messageID]) {
observer->handleMessage(messageID);
}
} else {
std::cout << "No observers for message: " << messageID << std::endl;
}
}
};
// 主函数
int main() {
Subject subject;
Observer1 observer1;
Observer2 observer2;
Observer3 observer3;
// 添加观察者
subject.addObserver(1, &observer1);
subject.addObserver(2, &observer1);
subject.addObserver(2, &observer2);
subject.addObserver(1, &observer3);
subject.addObserver(3, &observer3);
// 测试通知
subject.notifyObservers(1); // 消息1通知
subject.notifyObservers(2); // 消息2通知
subject.notifyObservers(3); // 消息3通知
subject.notifyObservers(4); // 无人订阅的消息
return 0;
}