当一个对象的内在状态改变时允许改变其行为，这个对象看起来像是改变了其类。
上下文环境（Context）：
它定义了客户程序需要的接口并维护一个具体状态角色的实例，将与状态相关的操作委托给当前的Concrete State对象来处理。
抽象状态（State）：
定义一个接口以封装使用上下文环境的的一个特定状态相关的行为。
具体状态（ConcreteState）：
实现抽象状态定义的接口。
1 //State.h
2 # ifndef _STATE_H_
3 # define _STATE_H_
4
5 class Context;
6
7 class State
8 {
9 public:
10 State();
11 virtual ~State();
12 virtual void OperationInterface(Context*);
13 virtual void OperationChangeState(Context*);
14 protected:
15 bool ChangeState(Context*, State*);
16 private:
17 };
18
19 class ConcreteStateA:public State
20 {
21 public:
22 ConcreteStateA();
23 virtual ~ConcreteStateA();
24 virtual void OperationInterface(Context*);
25 virtual void OperationChangeState(Context*);
26 protected:
27 private:
28 };
29
30 class ConcreteStateB:public State
31 {
32 public:
33 ConcreteStateB();
34 virtual ~ConcreteStateB();
35 virtual void OperationInterface(Context*);
36 virtual void OperationChangeState(Context*);
37 protected:
38 private:
39 };
40
41 # endif
1 //State.cpp
2 # include <iostream>
3 # include "State.h"
4 # include "Context.h"
5 using namespace std;
6
7 State::State()
8 {
9 cout << "Construct State" << endl;
10 }
11 State::~State()
12 {
13 cout << "Destruct State" << endl;
14 }
15 void State::OperationInterface(Context* con)
16 {
17 cout << "State::OperationInterface" << endl;
18 }
19 void State::OperationChangeState(Context* con)
20 {
21 cout << "State::OperationChangeState" << endl;
22 }
23 bool State::ChangeState(Context* con, State* st)
24 {
25 con->ChangeState(st);
26 return true;
27 }
28
29 ConcreteStateA::ConcreteStateA()
30 {
31 cout << "Construct ConcreteStateA" << endl;
32 }
33 ConcreteStateA::~ConcreteStateA()
34 {
35 cout << "Destruct ConcreteStateA" << endl;
36 }
37 void ConcreteStateA::OperationInterface(Context* con)
38 {
39 cout << "ConcreteStateA::OperationInterface" << endl;
40 }
41 void ConcreteStateA::OperationChangeState(Context* con)
42 {
43 OperationInterface(con);
44 this->ChangeState(con, new ConcreteStateB());
45 }
46
47 ConcreteStateB::ConcreteStateB()
48 {
49 cout << "Construct ConcreteStateB" << endl;
50 }
51 ConcreteStateB::~ConcreteStateB()
52 {
53 cout << "Destruct ConcreteStateB" << endl;
54 }
55 void ConcreteStateB::OperationInterface(Context* con)
56 {
57 cout << "ConcreteStateB::OperationInterface" << endl;
58 }
59 void ConcreteStateB::OperationChangeState(Context* con)
60 {
61 OperationInterface(con);
62 this->ChangeState(con, new ConcreteStateA());
63 }
1 //Context.h
2 # ifndef _CONTEXT_H_
3 # define _CONTEXT_H_
4
5 class State;
6 class Context
7 {
8 public:
9 Context();
10 Context(State*);
11 ~Context();
12 void OperationInterface();
13 void OperationChangeState();
14 protected:
15 private:
16 friend class State;
17 bool ChangeState(State*);
18 State* p_state;
19 };
20
21 # endif
1 //Context.cpp
2 # include <iostream>
3 # include "Context.h"
4 # include "State.h"
5 using namespace std;
6
7 Context::Context()
8 {
9 cout << "Construct Context" << endl;
10 }
11 Context::Context(State* state)
12 {
13 this->p_state = state;
14 cout << "Construct Context" << endl;
15 }
16 Context::~Context()
17 {
18 delete p_state;
19 cout << "Destruct Context" << endl;
20 }
21 void Context::OperationInterface()
22 {
23 p_state->OperationInterface(this);
24 }
25 bool Context::ChangeState(State* state)
26 {
27 this->p_state = state;
28 return true;
29 }
30 void Context::OperationChangeState()
31 {
32 p_state->OperationChangeState(this);
33 }
1 //main.cpp
2 # include <iostream>
3 # include "State.h"
4 # include "Context.h"
5 using namespace std;
6
7 int main()
8 {
9 State* st = new ConcreteStateA();
10 Context* con = new Context(st);
11 con->OperationInterface();
12 con->OperationInterface();
13 if(con != NULL)
14 delete con;
15 if(st != NULL)
16 st = NULL;
17 return 0;
18 }
result:
blank@linux-bai:~/Projects/State> g++ -o a *.cpp && ./a
Construct State
Construct ConcreteStateA
Construct Context
ConcreteStateA::OperationInterface
ConcreteStateA::OperationInterface
Destruct ConcreteStateA
Destruct State
Destruct Context
State Pattern（状态模式）,布布扣,bubuko.com
原文：http://www.cnblogs.com/blank031x/p/3872727.html