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

#ifndef Visitor_H_H
#define Visitor_H_H


#include <iostream>
#include <vector>
using namespace std;

class State
{
public:
    virtual void getManState() = 0;
    virtual void getWomanState() = 0;
    virtual ~State() {}

};

class StateHappy : public State
{
public:
    virtual void getManState(){
        cout << "Man drinks when happy!" << endl;
    }
    virtual void getWomanState(){
        cout << "Woman go shopping when happy!" << endl;
    }
};


class StateSad : public State
{
public:
    virtual void getManState(){
        cout << "Man smokes when sad!" << endl;
    }
    virtual void getWomanState(){
        cout << "Woman weeps when sad!" << endl;
    }

};


class People
{
public:
    virtual void visit(State *state) = 0;
    virtual ~People() {}
};

class Man : public People
{
public:
    virtual void visit(State *state){
        state->getManState();
    }
};

class Woman : public People
{
public:
    virtual void visit(State *state){
        state->getWomanState();
    }
};


class Visitor
{
public:
    Visitor() : state(NULL) {}
    void visit(){
        for(size_t i=0; i<vecPeople.size(); ++i){
            vecPeople[i]->visit(state);
        }
    }

    void addItem(People *people){
        vecPeople.push_back(people);
    }

    void setState(State *state0) { state = state0; }

private:
    vector<People*> vecPeople;
    State *state;
};


void VisitorTest()
{
    Visitor *visitor = new Visitor();
    visitor->addItem(new Man());
    visitor->addItem(new Woman());

    State *state1 = new StateHappy();
    State *state2 = new StateSad();

    visitor->setState(state1);
    visitor->visit();

    visitor->setState(state2);
    visitor->visit();

    delete visitor;
}

#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。