C++编程思想 第2卷 第10章 设计模式 观察者模式 观察者模式举例

具备了Observer和Observable头文件和内部类方法知识
看观察者模式的例子

//: C10:ObservedFlower.cpp
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// 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();
  getchar();
} ///:~

输出
Hummingbird A's breakfast time!
Bee B's breakfast time!
Bee A's breakfast time!
Hummingbird B's bed time!
Hummingbird A's bed time!
Bee B's bed time!
Hummingbird B's bed time!
Hummingbird A's bed time!
Bee B's bed time!

感兴趣的事件是Flower的打开或关闭
由于内部类方法的使用
两个事件成为可以独立进行观察的现象