//: C10:Observer.h // The Observer interface. #ifndef OBSERVER_H #define OBSERVER_H class Observable; class Argument {}; class Observer { public: // Called by the observed object, whenever // the observed object is changed: virtual void update(Observable* o, Argument* arg) = 0; virtual ~Observer() {} }; #endif // OBSERVER_H ///:~
Listado 9.30. C10/Observer.h
//: C10:Observable.h // The Observable class. #ifndef OBSERVABLE_H #define OBSERVABLE_H #include <set> #include "Observer.h" class Observable { bool changed; std::set<Observer*> observers; protected: virtual void setChanged() { changed = true; } virtual void clearChanged() { changed = false; } public: virtual void addObserver(Observer& o) { observers.insert(&o); } virtual void deleteObserver(Observer& o) { observers.erase(&o); } virtual void deleteObservers() { observers.clear(); } virtual int countObservers() { return observers.size(); } virtual bool hasChanged() { return changed; } // If this object has changed, notify all // of its observers: virtual void notifyObservers(Argument* arg = 0) { if(!hasChanged()) return; clearChanged(); // Not "changed" anymore std::set<Observer*>::iterator it; for(it = observers.begin();it != observers.end(); it++) (*it)->update(this, arg); } virtual ~Observable() {} }; #endif // OBSERVABLE_H ///:~
Listado 9.31. C10/Observable.h
//: C10:InnerClassIdiom.cpp // Example of the "inner class" idiom. #include <iostream> #include <string> using namespace std; class Poingable { public: virtual void poing() = 0; }; void callPoing(Poingable& p) { p.poing(); } class Bingable { public: virtual void bing() = 0; }; void callBing(Bingable& b) { b.bing(); } class Outer { string name; // Define one inner class: class Inner1; friend class Outer::Inner1; class Inner1 : public Poingable { Outer* parent; public: Inner1(Outer* p) : parent(p) {} void poing() { cout << "poing called for " << parent->name << endl; // Accesses data in the outer class object } } inner1; // Define a second inner class: class Inner2; friend class Outer::Inner2; class Inner2 : public Bingable { Outer* parent; public: Inner2(Outer* p) : parent(p) {} void bing() { cout << "bing called for " << parent->name << endl; } } inner2; public: Outer(const string& nm) : name(nm), inner1(this), inner2(this) {} // Return reference to interfaces // implemented by the inner classes: operator Poingable&() { return inner1; } operator Bingable&() { return inner2; } }; int main() { Outer x("Ping Pong"); // Like upcasting to multiple base types!: callPoing(x); callBing(x); } ///:~
Listado 9.32. C10/InnerClassIdiom.cpp
//: C10:ObservedFlower.cpp // Demonstration of "observer" pattern. #include <algorithm> #include <iostream> #include <string> #include <vector> #include "Observable.h" using namespace std; class Flower { bool isOpen; public: Flower() : isOpen(false), openNotifier(this), closeNotifier(this) {} void open() { // Opens its petals isOpen = true; openNotifier.notifyObservers(); closeNotifier.open(); } void close() { // Closes its petals isOpen = false; closeNotifier.notifyObservers(); openNotifier.close(); } // Using the "inner class" idiom: class OpenNotifier; friend class Flower::OpenNotifier; class OpenNotifier : public Observable { Flower* parent; bool alreadyOpen; public: OpenNotifier(Flower* f) : parent(f), alreadyOpen(false) {} void notifyObservers(Argument* arg = 0) { if(parent->isOpen && !alreadyOpen) { setChanged(); Observable::notifyObservers(); alreadyOpen = true; } } void close() { alreadyOpen = false; } } openNotifier; class CloseNotifier; friend class Flower::CloseNotifier; class CloseNotifier : public Observable { Flower* parent; bool alreadyClosed; public: CloseNotifier(Flower* f) : parent(f), alreadyClosed(false) {} void notifyObservers(Argument* arg = 0) { if(!parent->isOpen && !alreadyClosed) { setChanged(); Observable::notifyObservers(); alreadyClosed = true; } } void open() { alreadyClosed = false; } } closeNotifier; }; class Bee { string name; // An "inner class" for observing openings: class OpenObserver; friend class Bee::OpenObserver; class OpenObserver : public Observer { Bee* parent; public: OpenObserver(Bee* b) : parent(b) {} void update(Observable*, Argument *) { cout << "Bee " << parent->name << "'s breakfast time!" << endl; } } openObsrv; // Another "inner class" for closings: class CloseObserver; friend class Bee::CloseObserver; class CloseObserver : public Observer { Bee* parent; public: CloseObserver(Bee* b) : parent(b) {} void update(Observable*, Argument *) { cout << "Bee " << parent->name << "'s bed time!" << endl; } } closeObsrv; public: Bee(string nm) : name(nm), openObsrv(this), closeObsrv(this) {} Observer& openObserver() { return openObsrv; } Observer& closeObserver() { return closeObsrv;} }; class Hummingbird { string name; class OpenObserver; friend class Hummingbird::OpenObserver; class OpenObserver : public Observer { Hummingbird* parent; public: OpenObserver(Hummingbird* h) : parent(h) {} void update(Observable*, Argument *) { cout << "Hummingbird " << parent->name << "'s breakfast time!" << endl; } } openObsrv; class CloseObserver; friend class Hummingbird::CloseObserver; class CloseObserver : public Observer { Hummingbird* parent; public: CloseObserver(Hummingbird* h) : parent(h) {} void update(Observable*, Argument *) { cout << "Hummingbird " << parent->name << "'s bed time!" << endl; } } closeObsrv; public: Hummingbird(string nm) : name(nm), openObsrv(this), closeObsrv(this) {} Observer& openObserver() { return openObsrv; } Observer& closeObserver() { return closeObsrv;} }; int main() { Flower f; Bee ba("A"), bb("B"); Hummingbird ha("A"), hb("B"); f.openNotifier.addObserver(ha.openObserver()); f.openNotifier.addObserver(hb.openObserver()); f.openNotifier.addObserver(ba.openObserver()); f.openNotifier.addObserver(bb.openObserver()); f.closeNotifier.addObserver(ha.closeObserver()); f.closeNotifier.addObserver(hb.closeObserver()); f.closeNotifier.addObserver(ba.closeObserver()); f.closeNotifier.addObserver(bb.closeObserver()); // Hummingbird B decides to sleep in: f.openNotifier.deleteObserver(hb.openObserver()); // Something changes that interests observers: f.open(); f.open(); // It's already open, no change. // Bee A doesn't want to go to bed: f.closeNotifier.deleteObserver( ba.closeObserver()); f.close(); f.close(); // It's already closed; no change f.openNotifier.deleteObservers(); f.open(); f.close(); } ///:~
Listado 9.33. C10/ObservedFlower.cpp