轉自
http://m.shnenglu.com/unixfy/archive/2011/04/26/145077.htmlPart of the red marker to add by YeHao，Order oneself to better understand.
觀察者模式-設計模式來自于《大話設計模式》
觀察者模式：定義了一種一對多的依賴關系，讓多個觀察者對象同時監聽某一個主題對象。這個主題對象在狀態發生時，會通知所有觀察者對象，使他們自動更新自己。
行為型模式。
UML 類圖：
代碼實現 C++：
1 #include <iostream>
2 #include <string>
3 #include <list>
4 #include <algorithm>
5 using namespace std;
6
7 class Subject;
8
9 class Observer //觀察者
10 {
11 protected:
12 string name;
13 Subject* sub;
14 public:
15 Observer(const string& n, Subject* s) : name(n), sub(s) {}
16 virtual void Update() = 0;
17 };
18
19 class Subject //被觀察者
20 {
21 protected:
22 list<Observer*> observers;
23 string action;
24 public:
25 virtual void Attach(Observer* ob) = 0; //增加觀察者對象
26 virtual void Detach(Observer* ob) = 0; //移除觀察者對象
27 virtual void Notify() = 0;
28 virtual void setAction(const string& s) = 0;
29 virtual string getAction() = 0;
30 };
31
32 class StockObserver : public Observer
33 {
34 public:
35 StockObserver(const string& name, Subject* s) : Observer(name, s) {}
36 virtual void Update()
37 {
38 cout << sub->getAction() << '\t' << name << " 關閉股票行情，繼續工作！" << endl;
39 }
40 };
41
42 class NBAObserver : public Observer
43 {
44 public:
45 NBAObserver(const string& name, Subject* s) : Observer(name, s) {}
46 virtual void Update()
47 {
48 cout << sub->getAction() << '\t' << name << " 關閉 NBA，繼續工作！" << endl;
49 }
50 };
51
52 class Boss : public Subject
53 {
54 //private:
55 // list<Observer*> observers;
56 // string action;
57 public:
58 virtual void Attach(Observer* ob)
59 {
60 observers.push_back(ob);
61 }
62 virtual void Detach(Observer* ob)
63 {
64 list<Observer*>::iterator iter= find(observers.begin(), observers.end(), ob);
65 if (iter != observers.end())
66 {
67 observers.erase(iter);
68 }
69 }
70 virtual void Notify()
71 {
72 for (list<Observer*>::iterator iter = observers.begin(); iter != observers.end(); ++iter)
73 {
74 (*iter)->Update();
75 }
76 }
77 virtual void setAction(const string& s)
78 {
79 action = s;
80 }
81 virtual string getAction()
82 {
83 return action;
84 }
85 };
86
87 class Secretary : public Subject
88 {
89 //private:
90 // list<Observer*> observers;
91 // string action;
92 public:
93 virtual void Attach(Observer* ob)
94 {
95 observers.push_back(ob);
96 }
97 virtual void Detach(Observer* ob)
98 {
99 list<Observer*>::iterator iter = find(observers.begin(), observers.end(), ob);
100 if (iter != observers.end())
101 {
102 observers.erase(iter);
103 }
104 }
105 virtual void Notify()
106 {
107 for (list<Observer*>::iterator iter = observers.begin(); iter != observers.end(); ++iter)
108 {
109 (*iter)->Update();
110 }
111 }
112 virtual void setAction(const string& s)
113 {
114 action = s;
115 }
116 virtual string getAction()
117 {
118 return action;
119 }
120 };
121
122
123
124 int main()
125 {
126 Boss* huhansan = new Boss;
127 StockObserver* so = new StockObserver("abc", huhansan);
128 NBAObserver* no = new NBAObserver("xyz", huhansan);
129
130 huhansan->Attach(so);
131 huhansan->Attach(no);
132 huhansan->setAction("我胡漢三又回來了！");
133 huhansan->Notify();
134
135 huhansan->Detach(no);
136 huhansan->setAction("開會！");
137 huhansan->Notify();
138
139 delete huhansan;
140
141 Secretary* s = new Secretary;
142 s->Attach(no);
143 s->Attach(so);
144 s->setAction("老板來了！");
145 cout << s->getAction() << endl;
146 s->Notify();
147
148 delete so;
149 delete no;
150 delete s;
151
152 return 0;
153 }