设计模式——状态模式（State）

  • 定义：允许一个对象在其状态改变时，改变它的行为。看起来对象似乎修改了它的类。
  • 解决根据不同的对象状态进行不同的操作的问题
  • UML

  • 代码示例： 
      1 //==========================================
  2 //Context.h
  3 //==========================================
  4 #pragma once
  5 
  6 class State;
  7 class Context
  8 {
  9 public:
 10     Context(State* pState);
 11     ~Context();
 12     void Request();
 13 private:
 14     void UpdateState(State* pState);
 15     friend class ConcreteStateA;
 16     friend class ConcreteStateB;
 17 private:
 18     State* m_pState;
 19 };
 20 
 21 //==========================================
 22 //Context.cpp
 23 //==========================================
 24 #include "Context.h"
 25 #include <stdio.h>
 26 #include "State.h"
 27 
 28 Context::Context(State* pState)
 29     :m_pState(pState)
 30 {
 31 }
 32 
 33 Context::~Context()
 34 {
 35     delete m_pState;
 36 }
 37 
 38 void Context::Request()
 39 {
 40     if (NULL != m_pState)
 41     {
 42         m_pState->Handle(this);
 43     }
 44 }
 45 
 46 void Context::UpdateState(State* pState)
 47 {
 48     delete m_pState;
 49     m_pState = pState;
 50 }
 51 
 52 //==========================================
 53 //State.h
 54 //==========================================
 55 #pragma once
 56 
 57 class Context;
 58 class State
 59 {
 60 public:
 61     virtual ~State(){}
 62     virtual void Handle(Context* pContex) = 0;
 63 };
 64 
 65 class ConcreteStateA : public State
 66 {
 67 public:
 68     void Handle(Context* pContex);
 69 };
 70 
 71 class ConcreteStateB : public State
 72 {
 73 public:
 74     void Handle(Context* pContex);
 75 };
 76 
 77 //==========================================
 78 //State.cpp
 79 //==========================================
 80 #include "State.h"
 81 #include <iostream>
 82 #include "Context.h"
 83 using namespace std;
 84 
 85 //处理、更新状态
 86 void ConcreteStateA::Handle(Context* pContex)
 87 {
 88     cout<<"ConcreteStateA :: Handle"<<endl;
 89     pContex->UpdateState(new ConcreteStateB);
 90 }
 91 
 92 void ConcreteStateB::Handle(Context* pContex)
 93 {
 94     cout<<"ConcreteStateB :: Handle"<<endl;
 95     pContex->UpdateState(new ConcreteStateA);
 96 }
 97 
 98 //==========================================
 99 //main.cpp
100 //==========================================
101 #include "Context.h"
102 #include "State.h"
103 
104 int main()
105 {
106     State *pState = new ConcreteStateA();
107     Context *pContext = new Context(pState);
108     pContext->Request();
109     pContext->Request();
110     pContext->Request();
111 
112     delete pContext;
113 
114     return 0;
115 }
posted @ 2013-01-04 11:18  iThinking  阅读(256)  评论(0)  编辑  收藏  举报