設計模式C++之十四（Iterator迭代器模式）

14.1.解釋

概念：提供一種方法順序訪問一個聚合對象中各個元素，而又不需暴露該對象的內部表示。

main()，客戶

IProject，產品接口

CProject，產品類

IIterator，迭代器接口

IProjectIterator，產品迭代器接口

CProjectIterator，產品迭代器實現類

說明：CProject實現產品類，能夠返回一個迭代器的指針。這個迭代器將封裝產品類裏的一個數組。所以迭代器在運行Next函數時，可以遍歷這個數組的所有元素。

簡單來說，就是用代碼實現vector<int>::iterator或vector<int>::const_iterator。

我們來看代碼：

//IProject.h

#pragma once
#include "IProjectIterator.h"
#include <iostream>
using std::string;
class IProject
{
public:
    IProject(void)
    {
    }
    virtual ~IProject(void)
    {
    }
    virtual void Add(string name, int num, int cost) = 0;
    virtual string GetProjectInfo() = 0;
    virtual IProjectIterator* GetIterator() = 0;
    virtual void Erase() = 0;
};

//Project.h

#pragma once
#include "iproject.h"
#include "IProjectIterator.h"
#include <iostream>
#include <vector>
using std::string;
using std::vector;
class CProject :
    public IProject
{
public:
    CProject(void);
    CProject(string name, int num, int cost);
    ~CProject(void);
    string GetProjectInfo();
    void Add(string name, int num, int cost);
    IProjectIterator * GetIterator();
    void Erase();
private:
    string m_name;
    int m_num;
    int m_cost;
    vector<IProject*> m_projectList;
};

//Project.cpp

#include "StdAfx.h"
#include "Project.h"
#include "..\CommonDeclare\Convert.h"
#include "ProjectIterator.h"
#include <iostream>
#include <vector>
using std::string;
using std::vector;
CProject::CProject( void )
{
    m_name = "";
    m_num = 0;
    m_cost = 0;
}
CProject::CProject(string name, int num, int cost) :m_name(name), m_num(num), m_cost(cost)
{
}
CProject::~CProject(void)
{
}
string CProject::GetProjectInfo()
{
    string info = "";
    info.append("項目名稱是：");
    info.append(this->m_name);
    info.append("\t項目人數：");
    info.append(CConvert::ToString(m_num));
    info.append("\t項目費用：");
    info.append(CConvert::ToString(m_cost));
    return info;
}
void CProject::Add( string name, int num, int cost )
{
    this->m_projectList.push_back(new CProject(name, num, cost));
}
IProjectIterator * CProject::GetIterator()
{
    return new CProjectIterator(this->m_projectList);
}
void CProject::Erase()
{
    vector<IProject*>::reverse_iterator projectDelIt = m_projectList.rbegin();
    for (; projectDelIt != m_projectList.rend(); projectDelIt++)
    {
        delete (*projectDelIt);
        (*projectDelIt) = NULL;
    }
    m_projectList.clear();
}

//IIterator.h

#pragma once
class IProject;
class IIterator
{
public:
    IIterator(void)
    {
    }
    virtual ~IIterator(void)
    {
    }
    virtual bool HasNext() = 0;
    virtual IProject * Next() = 0;
};

//IProjectIterator.h

#pragma once
#include "iiterator.h"
class IProject;
class IProjectIterator :
    public IIterator
{
public:
    IProjectIterator(void)
    {
    }
    virtual ~IProjectIterator(void)
    {
    }
    virtual bool HasNext() = 0;
    virtual IProject * Next() = 0;
};

//ProjectIterator.h

#pragma once
#include "iprojectiterator.h"
#include "IProject.h"
#include <vector>
using std::vector;
class CProjectIterator :
    public IProjectIterator
{
public:
    CProjectIterator(vector<IProject *> pl);
    ~CProjectIterator(void);
    bool HasNext();
    IProject * Next();
private:
    vector<IProject *> m_projectList;
    size_t m_currentItem;
};

//ProjectIterator.cpp

#include "StdAfx.h"
#include "ProjectIterator.h"
CProjectIterator::CProjectIterator(vector<IProject *> pl) : m_projectList(pl)
{
    m_currentItem = 0;
}
CProjectIterator::~CProjectIterator(void)
{
}
bool CProjectIterator::HasNext()
{
    bool b = true;
    if (m_currentItem >= m_projectList.size())
        b = false;
    return b;
}
IProject * CProjectIterator::Next()
{
    IProject *pp = m_projectList.at(m_currentItem ++);
    return pp;
}

// Iterator.cpp
#include "stdafx.h"
#include "IProject.h"
#include "Project.h"
#include "..\CommonDeclare\Convert.h"
#include "ProjectIterator.h"
#include <iostream>
#include <vector>
using std::vector;
using std::cout;
using std::endl;
void DoIt()
{
    cout << "----------未使用迭代模式----------" << endl;
    vector<IProject*> projectList;

    projectList.push_back(new CProject("星球大戰項目", 10, 100000));
    projectList.push_back(new CProject("扭轉時空項目", 100, 10000000));
    projectList.push_back(new CProject("超人改造項目", 10000, 1000000000));

    for (int i = 4; i < 6; i ++)
    {
        string name = "";
        name.append("第");
        name.append(CConvert::ToString(i));
        name.append("個項目");
        projectList.push_back(new CProject(name, i * 5, i * 1000000));
    }

    vector<IProject*>::const_iterator projectIt = projectList.begin();
    for (; projectIt != projectList.end(); projectIt++)
        cout << (*projectIt)->GetProjectInfo().c_str() << endl;

    vector<IProject*>::reverse_iterator projectDelIt = projectList.rbegin();
    for (; projectDelIt != projectList.rend(); projectDelIt++)
    {
        delete (*projectDelIt);
        (*projectDelIt) = NULL;
    }
    projectList.clear();
}
void DoNew()
{
    cout << "----------使用迭代模式----------" << endl;
    IProject *pproject = new CProject();
    pproject->Add("星球大戰項目", 10, 100000);
    pproject->Add("扭轉時空項目", 100, 10000000);
    pproject->Add("超人改造項目", 10000, 1000000000);

    for (int i = 4; i < 6; i ++)
    {
        string name = "";
        name.append("第");
        name.append(CConvert::ToString(i));
        name.append("個項目");
        pproject->Add(name, i * 5, i * 1000000);
    }

    IProjectIterator *pprojectIt = pproject->GetIterator();
    while(pprojectIt->HasNext())
    {
        IProject *p = dynamic_cast<IProject*>(pprojectIt->Next());
        cout << p->GetProjectInfo().c_str() << endl;
    }
    delete pprojectIt;
    pprojectIt = NULL;
    pproject->Erase();
    delete pproject;
    pproject = NULL;
}
int _tmain(int argc, _TCHAR* argv[])
{
    //使用Iterator模式之前
    DoIt();

    //使用Iterator
    DoNew();

    _CrtSetDbgFlag(_CRTDBG_LEAK_CHECK_DF | _CRTDBG_ALLOC_MEM_DF);
    _CrtDumpMemoryLeaks();

    return 0;
}

這個模式，可能有一點繞，需要再仔細的思考一番。本來希望把模式的工作方式，用最簡單易懂的語言來總結，但其實這個總結更難。簡單的模式還容易些理解，也容易總結，複雜的就難了。打算在之後，學習數據結構的過程中，都總結出這樣一句話來。很期待後面對數據結構的學習，發現自己越來越愛學習了。