设计模式13——访问者模式

访问者模式中，有一个数据体，添加了各个访问对象。这些访问对象在不同的状态时，会有不同的反应。这种模式中，对象与状态相分离，互不干扰。

Visitor.h内容

  1 #ifndef Visitor_H_H
  2 #define Visitor_H_H
  3
  4
  5 #include <iostream>
  6 #include <vector>
  7 using namespace std;
  8
  9 class State
 10 {
 11 public:
 12     virtual void getManState() = 0;
 13     virtual void getWomanState() = 0;
 14     virtual ~State() {}
 15
 16 };
 17
 18 class StateHappy : public State
 19 {
 20 public:
 21     virtual void getManState(){
 22         cout << "Man drinks when happy!" << endl;
 23     }
 24     virtual void getWomanState(){
 25         cout << "Woman go shopping when happy!" << endl;
 26     }
 27 };
 28
 29
 30 class StateSad : public State
 31 {
 32 public:
 33     virtual void getManState(){
 34         cout << "Man smokes when sad!" << endl;
 35     }
 36     virtual void getWomanState(){
 37         cout << "Woman weeps when sad!" << endl;
 38     }
 39
 40 };
 41
 42
 43 class People
 44 {
 45 public:
 46     virtual void visit(State *state) = 0;
 47     virtual ~People() {}
 48 };
 49
 50 class Man : public People
 51 {
 52 public:
 53     virtual void visit(State *state){
 54         state->getManState();
 55     }
 56 };
 57
 58 class Woman : public People
 59 {
 60 public:
 61     virtual void visit(State *state){
 62         state->getWomanState();
 63     }
 64 };
 65
 66
 67 class Visitor
 68 {
 69 public:
 70     Visitor() : state(NULL) {}
 71     void visit(){
 72         for(size_t i=0; i<vecPeople.size(); ++i){
 73             vecPeople[i]->visit(state);
 74         }
 75     }
 76
 77     void addItem(People *people){
 78         vecPeople.push_back(people);
 79     }
 80
 81     void setState(State *state0) { state = state0; }
 82
 83 private:
 84     vector<People*> vecPeople;
 85     State *state;
 86 };
 87
 88
 89 void VisitorTest()
 90 {
 91     Visitor *visitor = new Visitor();
 92     visitor->addItem(new Man());
 93     visitor->addItem(new Woman());
 94
 95     State *state1 = new StateHappy();
 96     State *state2 = new StateSad();
 97
 98     visitor->setState(state1);
 99     visitor->visit();
100
101     visitor->setState(state2);
102     visitor->visit();
103
104     delete visitor;
105 }
106
107 #endif

运行结果：

实例中，男士和女士在高兴和悲伤时会有不同的动作反应，由一个visitor添加所有People的实例后，设置不同的状态以对每个个体进行访问。