观察者模式-C++实现

观察者模式概念：定义对象间的一种一对多的依赖关系，以便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自动更新。“Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.” GoF

UML图

特点：

1.观察者模式定义了对象之间一对多的关系。

2.主题（也就是可观察者）用一个共同的接口来更新观察者。

3.观察者和可观察者用松耦合的方式结合，可观察者不知道观察者的细节，只知道观察者实现了观察者接口

4.有多个观察者时，不可以依赖特点的通知次序。

C++源代码：

Observer.h

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1. /*
2. 观察者模式：在对象之间定义一对多的依赖，这样一来，当一个对象改变状态，
3. 依赖它的对象都会收到通知，并自动更新。
4. */
6. #include <iostream>
7. #include <vector>
8. using namespace std;
10. class Observer;
12. //Account抽象类，用作接口
13. class Account
14. {
15. protected:
16. vector<Observer*> observer;
17. double balance;
18. public:
19. virtual void add_observer(Observer *o)=0;
20. virtual void remove_observer(Observer *o)=0;
21. virtual void notify_observer()=0;
22. virtual void set_balance(double balance)=0;
23. virtual double get_balance()=0;
24. public:
25. virtual ~Account()
26. {
27. cout<<"in the destructor of Account"<<endl;
28. }
29. };
31. //Observer抽象类，用作接口
32. class Observer
33. {
34. protected:
35. Account *account;
36. public:
37. Observer(Account *account):account(account) {}
38. virtual void handle_event()=0;
39. virtual void set_account_balance(double balance)=0;
40. virtual ~Observer()
41. {
42. cout<<"in the destructor of Observer"<<endl;
43. }
44. };
46. //BankAccount具体类，继承了ACcount抽象类
47. class BankAccount:public Account
48. {
49. public:
51. ~BankAccount()
52. {
53. cout<<"in the destructor of BankAccount"<<endl;
54. }
56. public:
57. void add_observer(Observer *o)
58. {
59. observer.push_back(o);
60. }
61. void remove_observer(Observer *o)
62. {
63. for(vector<Observer*>::iterator it=observer.begin(); it!=observer.end(); it++)
64. {
65. if(o==*it)
66. {
67. observer.erase(it);
68. return;
69. }
70. }
71. }
72. void notify_observer()
73. {
74. for(vector<Observer*>::const_iterator it=observer.begin(); it!=observer.end(); it++)
75. {
76. (*it)->handle_event();
77. }
78. }
79. void set_balance(double balance)
80. {
81. this->balance=balance;
82. notify_observer();
83. }
84. double get_balance()
85. {
86. return balance;
87. }
89. };
91. class ATM:public Observer
92. {
93. public:
94. ATM(Account *account):Observer(account)//将acount传递给基类Observer的构造函数
95. {
96. }
97. ~ATM()
98. {
99. cout<<"in the destructor of ATM"<<endl;
100. }
101. public:
102. void handle_event()
103. {
104. cout<<"ATM: the balance of bank accont is changed to "<<account->get_balance()<<endl;
105. }
106. void set_account_balance(double balance)
107. {
108. account->set_balance(balance);
109. }
110. };
112. class InternetBankService:public Observer
113. {
114. public:
115. InternetBankService(Account *account):Observer(account) {}
116. ~InternetBankService()
117. {
118. cout<<"in the destructor InternetBankService "<<endl;
119. }
120. public:
121. void handle_event()
122. {
123. cout<<"IBS: the balance of bank account is changed to:"<<account->get_balance()<<endl;
124. }
125. void set_account_balance(double balance)
126. {
127. account->set_balance(balance);
128. }
130. };

Observer.cpp

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1. #include "Observer.h"
2. int main(int argc, char **argv)
3. {
4. Account *account=new BankAccount();
5. Observer *atm_observer=new ATM(account);
6. Observer *ibs_observer=new InternetBankService(account);
8. account->add_observer(atm_observer);
9. account->add_observer(ibs_observer);
11. account->set_balance(1000.12);
13. cout<<"Event is triggered by atm_observer"<<endl;
14. cout<<"============="<<endl;
15. atm_observer->set_account_balance(1000.23);
17. cout<<"Event is triggered by ibs_observer"<<endl;
18. cout<<"============="<<endl;
19. ibs_observer->set_account_balance(1000.36);
21. delete atm_observer;
22. delete ibs_observer;
23. return 0;
24. }

例2：

Test_Observer.cpp

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1. /*
2. 千万要注意对象分割问题的出现。一定要理解。
3. */
4. #include <iostream>
5. #include <string>
6. #include <vector>
7. using namespace std;
9. class Observer
10. {
11. protected:
12. string name;
13. public:
14. virtual void update()
15. {
16. cout<<"Observer"<<endl;
17. }
18. };
20. class Man:public Observer
21. {
22. public:
23. Man(string name)
24. {
25. this->name=name;
26. }
27. void update()
28. {
29. cout<<name<<" Man is coming"<<endl;
30. }
31. };
32. class Woman:public Observer
33. {
34. public:
35. Woman(string name)
36. {
37. this->name=name;
38. }
39. void update()
40. {
41. cout<<name<<" Woman is leaving"<<endl;
42. }
43. };
45. class Subject
46. {
47. private:
48. vector<Observer*> obser;
49. public:
50. void add(Observer &ob)
51. {
52. obser.push_back(&ob);
53. }
54. void notify()
55. {
56. for (vector<Observer*>::iterator it=obser.begin(); it!=obser.end(); it++)
57. {
58. (*it)->update();
59. }
60. }
61. };
63. int main()
64. {
65. Subject secret;
66. Man m1("m1--");
67. Man m2("m2--");
68. Woman w1("w1");
69. Woman w2("w2");
71. secret.add(m1);
72. secret.add(m2);
73. secret.add(w1);
74. secret.add(w2);
76. secret.notify();
77. return 0;
79. }