C++ Observer Pattern‌ Base

C++ObserverPattern‌Base.cpp

#include <iostream>
#include <set>

using namespace std;

// ---------------- Observer interface -----------------
class MyObserver {
  public:
	virtual void Notify() = 0;
};

// ---------------- Observable object -------------------
class MyObservable {
	static MyObservable *instance;
	set<MyObserver *> observers;
	MyObservable(){};

  public:
	static MyObservable *GetInstance();
	void AddObserver(MyObserver &o);
	void RemoveObserver(MyObserver &o);
	void NotifyObservers();
	void Trigger();
};

MyObservable *MyObservable::instance = NULL;

MyObservable *MyObservable::GetInstance()
{
	if (instance == NULL) {
	instance = new MyObservable();
	}

	return instance;
}

void MyObservable::AddObserver(MyObserver &o) { observers.insert(&o); }

void MyObservable::RemoveObserver(MyObserver &o) { observers.erase(&o); }

void MyObservable::NotifyObservers()
{
	set<MyObserver *>::iterator itr;
	for (itr = observers.begin(); itr != observers.end(); itr++)
	(*itr)->Notify();
}

// TEST METHOD TO TRIGGER
// IN THE REAL SCENARIO THIS IS NOT REQUIRED
void MyObservable::Trigger() { NotifyObservers(); }

// ------ Concrete class interested in notifications ---
class MyClass : public MyObserver {

	MyObservable *observable;

  public:
	MyClass()
	{
	observable = MyObservable::GetInstance();
	observable->AddObserver(*this);
	}

	~MyClass() { observable->RemoveObserver(*this); }

	void Notify() { cout << "Received a change event" << endl; }
};

int main()
{
	MyObservable *observable = MyObservable::GetInstance();
	MyClass *obj = new MyClass();
	observable->Trigger();

	return 0;
}