观察者模式

1.定义

在GOF的《设计模式:可复用面向对象软件的基础》一书中对观察者模式是这样说的：定义对象间的一种一对多的依赖关系，当一个对象的状态发生改变时，所有依赖于它的对象都得到通知并被自动更新。

2.代码简单实现

 1 #include<iostream>
 2 #include<string>
 3 #include<list>
 4 using namespace std;
 5 class AbObserver
 6 {
 7 public:
 8     virtual void getMessage(string message) = 0;
 9 };
10 
11 class AbSecretary
12 {
13 public:
14     virtual void sendMessage(string message) = 0;
15     virtual void addObserver(AbObserver * observer) = 0;
16 };
17 //开小差的同事类（观察者）
18 class Observer:public AbObserver
19 {
20 public:
21     void getMessage(string message)
22     {
23         cout << message << endl;
24     }
25 };
26 //秘书类（主题对象，通知者）
27 class Secretary:public AbSecretary
28 {
29 public:
30     void sendMessage(string message)
31     {
32         for (list<AbObserver *>::iterator it = observers.begin(); it != observers.end(); it++)
33         {
34             (*it)->getMessage(message);
35         }
36     }
37     void addObserver(AbObserver * observer)
38     {
39         observers.push_back(observer);
40     }
41 private:
42     list<AbObserver *> observers;
43 };
44 
45 int main()
46 {
47     Observer *observer1 = new Observer;
48     Observer *observer2 = new Observer;
49     Secretary * secretary = new Secretary;
50     secretary->addObserver(observer1);
51     secretary->addObserver(observer2);
52     secretary->sendMessage("老板来了");
53     secretary->sendMessage("老板走了");
54     system("pause");
55     return 0;
56 }