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https://github.com/JakubVojvoda/design-patterns-cpp.git
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126 lines
2.3 KiB
C++
126 lines
2.3 KiB
C++
/*
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* C++ Design Patterns: Observer
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* Author: Jakub Vojvoda [github.com/JakubVojvoda]
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* 2016
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*
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* Source code is licensed under MIT License
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* (for more details see LICENSE)
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*
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*/
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#include <iostream>
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#include <vector>
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class Subject;
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/*
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* Observer
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* defines an updating interface for objects that should be notified
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* of changes in a subject
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*/
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class Observer {
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public:
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virtual int getState() = 0;
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virtual void update(Subject *subject) = 0;
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// ...
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};
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/*
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* Concrete Observer
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* stores state of interest to ConcreteObserver objects and
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* sends a notification to its observers when its state changes
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*/
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class ConcreteObserver : public Observer {
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public:
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ConcreteObserver(int state)
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: observer_state(state) {}
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int getState() {
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return observer_state;
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}
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void update(Subject *subject);
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// ...
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private:
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int observer_state;
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// ...
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};
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/*
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* Subject
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* knows its observers and provides an interface for attaching
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* and detaching observers
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*/
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class Subject {
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public:
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void attach(Observer *observer) {
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observers.push_back(observer);
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}
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void detach(int index) {
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observers.erase(observers.begin() + index);
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}
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void notify() {
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for (unsigned int i = 0; i < observers.size(); i++) {
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observers.at(i)->update(this);
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}
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}
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virtual int getState() = 0;
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virtual void setState(int s) = 0;
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// ...
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private:
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std::vector<Observer *> observers;
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// ...
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};
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/*
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* Concrete Subject
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* stores state that should stay consistent with the subject's
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*/
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class ConcreteSubject : public Subject {
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public:
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int getState() {
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return subject_state;
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}
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void setState(int s) {
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subject_state = s;
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}
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// ...
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private:
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int subject_state;
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// ...
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};
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void ConcreteObserver::update(Subject *subject) {
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observer_state = subject->getState();
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std::cout << "Observer state updated." << std::endl;
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}
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int main()
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{
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ConcreteObserver observer1(1);
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ConcreteObserver observer2(2);
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std::cout << "Observer 1 state: " << observer1.getState() << std::endl;
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std::cout << "Observer 2 state: " << observer2.getState() << std::endl;
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Subject *subject = new ConcreteSubject;
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subject->attach(&observer1);
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subject->attach(&observer2);
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subject->setState(10);
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subject->notify();
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std::cout << "Observer 1 state: " << observer1.getState() << std::endl;
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std::cout << "Observer 2 state: " << observer2.getState() << std::endl;
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return 0;
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}
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