设计模式C++学习笔记之十八（Visitor访问者模式）

博文很精彩，为方便个人学习特转载，地址：http://www.cnblogs.com/wanggary/archive/2011/04/21/2024099.html

18.1.解释

概念：表示一个作用于某对象结构中的各元素的操作。它使你可以在不改变各元素的类的前提下定义作用于这些元素的新操作。

main()，客户

IVisitor，访问者接口

CBaseVisitor，访问者实现类

CEmployee，被访问者抽象类

CCommonEmployee，被访问者实现类之一

CManager，被访问者实现类之二

说明：A接受B的访问，B主动的执行访问动作。

注意：和观察者的区别是，被观察者要执行一个动作，然后主动发送通知给观察者。访问者模式是由访问者主动发出的动作。

看代码：

//IVisitor.h
#pragma once

class CCommonEmployee;
class CManager;
class IVisitor
{
public:

    IVisitor(void)
    {
    }

    virtual ~IVisitor(void)
    {
    }
    virtual void Visit(CCommonEmployee commonEmployee) = 0;
    virtual void Visit(CManager manager) = 0;
    virtual int GetTotalSalary() = 0;
};

//BaseVisitor.h
#pragma once
#include "ivisitor.h"
#include "CommonEmployee.h"
#include "Manager.h"
#include <iostream>
using std::string;
class CBaseVisitor :
    public IVisitor
{
public:
    CBaseVisitor(void);
    ~CBaseVisitor(void);
    void Visit(CCommonEmployee commonEmployee);
    void Visit(CManager manager);
    int GetTotalSalary();
private:
    string GetBasicInfo(CEmployee *pemployee);
    string GetManagerInfo(CManager manager);
    string GetCommonEmployee(CCommonEmployee employee);
    static const int MANAGER_COEFFICENT = 5;
    static const int COMMONEMPLOYEE_COEFFICENT = 2;
    int m_commonTotal;
    int m_managerTotal;
    void CalCommonSalary(int salary);
    void CalManagerSalary(int salary);
};

//BaseVisitor.cpp
#include "StdAfx.h"
#include "..\CommonDeclare\Convert.h"
#include "BaseVisitor.h"
#include <iostream>
using std::string;
using std::cout;
using std::endl;

CBaseVisitor::CBaseVisitor(void)
{
    m_commonTotal = 0;
    m_managerTotal = 0;
}

CBaseVisitor::~CBaseVisitor(void)
{
}

void CBaseVisitor::Visit(CCommonEmployee commonEmployee)
{
    cout << this->GetCommonEmployee(commonEmployee).c_str() << endl;
    this->CalCommonSalary(commonEmployee.GetSalary());
}

void CBaseVisitor::Visit(CManager manager)
{
    cout << this->GetManagerInfo(manager).c_str() << endl;
    this->CalManagerSalary(manager.GetSalary());
}

string CBaseVisitor::GetBasicInfo(CEmployee *pemployee)
{
    string info = "";
    info.append("姓名：");
    info.append(pemployee->GetName());
    info.append("\t");
    info.append("性别：");
    info.append(CConvert::ToString(pemployee->GetSex()));
    info.append("\t");
    info.append("薪水：");
    info.append(CConvert::ToString(pemployee->GetSalary()));
    info.append("\t");
    return info;
}

string CBaseVisitor::GetManagerInfo(CManager manager)
{
    string basicInfo = this->GetBasicInfo(&manager);
    string otherInfo = "";
    otherInfo.append("业绩：");
    otherInfo.append(manager.GetPerformance());
    otherInfo.append("\t");
    basicInfo.append(otherInfo);
    return basicInfo;
}

string CBaseVisitor::GetCommonEmployee(CCommonEmployee employee)
{
    string basicInfo = this->GetBasicInfo(&employee);
    string otherInfo = "";
    otherInfo.append("工作：");
    otherInfo.append(employee.GetJob());
    otherInfo.append("\t");
    basicInfo.append(otherInfo);
    return basicInfo;
}

int CBaseVisitor::GetTotalSalary()
{
    return this->m_commonTotal + this->m_managerTotal;
}

void CBaseVisitor::CalCommonSalary(int salary)
{
    this->m_commonTotal += salary;
}

void CBaseVisitor::CalManagerSalary(int salary)
{
    this->m_managerTotal += salary;
}

//Employee.h
#pragma once
#include "IVisitor.h"
#include <iostream>
using std::string;
class CEmployee
{
public:
static int MALE;
static int FEMALE;
CEmployee(void);
virtual ~CEmployee(void);
string GetName();
void SetName(string name);
int GetSalary();
void SetSalary(int v);
int GetSex();
void SetSex(int v);
virtual void Accept(IVisitor *pVisitor) = 0;
private:
string m_name;
int m_salary;
int m_sex;
};

//Employee.cpp
#include "StdAfx.h"
#include "Employee.h"
int CEmployee::MALE = 0;
int CEmployee::FEMALE = 1;

CEmployee::CEmployee(void)
{
}

CEmployee::~CEmployee(void)
{
}

string CEmployee::GetName()
{
return m_name;
}

void CEmployee::SetName( string name )
{
m_name = name;
}

int CEmployee::GetSalary()
{
return m_salary;
}

void CEmployee::SetSalary( int v )
{
m_salary = v;
}

int CEmployee::GetSex()
{
return m_sex;
}

void CEmployee::SetSex( int v )
{
m_sex = v;
}

//Manager.h
#pragma once
#include "employee.h"
#include "IVisitor.h"
#include <iostream>
using std::string;
class CManager :
public CEmployee
{
public:
CManager(void);
~CManager(void);
string GetPerformance();
void SetPerformance(string per);
void Accept(IVisitor *pVisitor);
protected:
string GetOtherInfo();
private:
string m_performance;
};

//Manager.cpp
#include "StdAfx.h"
#include "Manager.h"
#include <iostream>
using std::string;

CManager::CManager(void)
{
this->m_performance = "";
}

CManager::~CManager(void)
{
}

string CManager::GetPerformance()
{
return m_performance;
}

void CManager::SetPerformance(string per)
{
this->m_performance = per;
}

string CManager::GetOtherInfo()
{
string info = "";
info.append("业绩：");
info.append(this->m_performance);
info.append("\t");
return info;
}

void CManager::Accept(IVisitor *pVisitor)
{
pVisitor->Visit(*this);
}

// Visitor.cpp : 定义控制台应用程序的入口点。
//
#include "stdafx.h"
#include "Employee.h"
#include "CommonEmployee.h"
#include "Manager.h"
#include "BaseVisitor.h"
#include "..\CommonDeclare\Convert.h"
#include <vector>
#include <iostream>
using std::vector;
using std::cout;
using std::endl;

void MockEmployee(vector<CEmployee*> *pvce)
{
CCommonEmployee *pZhangSan = new CCommonEmployee();
pZhangSan->SetJob("编写Java程序，绝对的蓝领、苦工加搬运工");
pZhangSan->SetName("张三");
pZhangSan->SetSalary(1800);
pZhangSan->SetSex(CEmployee::MALE);
pvce->push_back(pZhangSan);

CCommonEmployee *pLiSi = new CCommonEmployee();
pLiSi->SetJob("页面美工，审美素质太不流行了！");
pLiSi->SetName("李四");
pLiSi->SetSalary(1900);
pLiSi->SetSex(CEmployee::FEMALE);
pvce->push_back(pLiSi);

CManager *pWangWu = new CManager();
pWangWu->SetPerformance("基本上是负值，但是我会拍马屁呀");
pWangWu->SetName("王五");
pWangWu->SetSalary(1900);
pWangWu->SetSex(CEmployee::FEMALE);
pvce->push_back(pWangWu);
}

void DoIt()
{
vector<CEmployee*> vce;
MockEmployee(&vce);
vector<CEmployee*>::const_iterator readIt = vce.begin();

CBaseVisitor visitor;
for (; readIt != vce.end(); readIt ++)
{
(*readIt)->Accept(&visitor);
}
cout << "本公司的月工资总额是：" << CConvert::ToString(visitor.GetTotalSalary()).c_str() << endl;

vector<CEmployee*>::reverse_iterator delIt = vce.rbegin();
for (; delIt != vce.rend(); delIt++)
{
delete (*delIt);
(*delIt) = NULL;
}
vce.clear();
}

int _tmain(int argc, _TCHAR* argv[])
{
DoIt();
return 0;
}

访问者模式属于行为型模式。访问者模式是由访问者主动发出的动作。