[设计模式]Iterator迭代器模式

问题

iterator模式应该是最为熟悉的模式了，最简单的证明就是在实现Composite模式，Flyweight模式，Observer模式中就直接用到了STL提供的Iterator来遍历Vector或者List数据结构。

Iterator模式也正是用来解决对一个聚合对象的遍历问题，将对聚合的遍历封装到一个类中进行，这样就避免了暴露这个聚合对象的内部表示的可能。

iterator迭代器模式

提供一种方法顺序访问一个聚合对象中各个元素, 而又不需暴露该对象的内部表示。

小demo

iterator.h

#ifndef ITERATOR_H
#define ITERATOR_H

typedef int DATA;
class Iterater;
// 容器的抽象基类
class Aggregate
{
public:
	virtual ~Aggregate(){}
	virtual Iterater* CreateIterater(Aggregate *pAggregate) = 0;
	virtual int GetSize() = 0;
	virtual DATA GetItem(int nIndex) = 0;
};

// 迭代器的抽象基类
class Iterater
{
public:
	virtual ~Iterater(){}

	virtual void First()		= 0;
	virtual void Next()			= 0;
	virtual bool IsDone()		= 0;
	virtual DATA CurrentItem()	= 0; 
};

// 一个具体的容器类,这里是用数组表示
class ConcreateAggregate	: public Aggregate
{
public:
	ConcreateAggregate(int nSize);
	virtual ~ConcreateAggregate();
	virtual Iterater* CreateIterater(Aggregate *pAggregate);
	virtual int GetSize();
	virtual DATA GetItem(int nIndex);
private:
	int m_nSize;
	DATA *m_pData;
};

// 访问ConcreateAggregate容器类的迭代器类
class ConcreateIterater : public Iterater
{
public:
	ConcreateIterater(Aggregate* pAggregate);
	virtual ~ConcreateIterater(){}

	virtual void First();
	virtual void Next();
	virtual bool IsDone();
	virtual DATA CurrentItem();
private:
	Aggregate  *m_pConcreateAggregate;
	int			m_nIndex;
};

#endif

 

iterator.cpp

#include <iostream>
#include "Iterator.h"

ConcreateAggregate::ConcreateAggregate(int nSize) : m_nSize(nSize), m_pData(NULL)
{
	m_pData = new DATA[m_nSize];
	
	for (int i = 0; i < nSize; ++i)
	{
		m_pData[i] = i;
	}
}

ConcreateAggregate::~ConcreateAggregate()
{
	delete [] m_pData;
	m_pData = NULL;
}

Iterater* ConcreateAggregate::CreateIterater(Aggregate *pAggregate)
{
	return new ConcreateIterater(this);
}

int ConcreateAggregate::GetSize()
{
	return m_nSize;
}

 

main.cpp

#include "Iterator.h"
#include <iostream>

int main()
{
	Aggregate* pAggregate = new ConcreateAggregate(4);
	Iterater*  pIterater  = new ConcreateIterater(pAggregate);

	for (; false == pIterater->IsDone(); pIterater->Next())
	{
		std::cout << pIterater->CurrentItem() << std::endl;
	}
    system("pause");
	return 0;
}