设计模式(二十一)迭代器模式

意图：提供一种方法顺序访问一个聚合对象中各个元素, 而又无须暴露该对象的内部表示。

当需要访问一个聚集对象，且不论这个对象是什么都需要遍历的时候就应该考虑迭代器模式

#include <iostream>
using namespace std;
typedef int Object;
#define SIZE 5 

class MyIterator
{
public:
  virtual void First() = 0;
  virtual void Next() = 0;
  virtual bool IsDone() = 0;
  virtual Object CurrentItem() = 0;
};

class Aggregate
{
public:
  virtual MyIterator *CreateIterator() = 0;
  virtual Object getItem(int index) = 0;
  virtual int getSize() = 0;
};

class ContreteIterator : public MyIterator
{
public:
  ContreteIterator(Aggregate *ag)
  {
    _ag = ag;
    _current_index = 0;
  }

  virtual void First()
  {
    _current_index = 0;  //让当前 游标 回到位置0
  }

  virtual void Next()
  {
    if (_current_index < _ag->getSize())
    {
      _current_index++;
    }
  }

  virtual bool IsDone()
  {
    return  (_current_index == _ag->getSize());
  }

  virtual Object CurrentItem()
  {
    return _ag->getItem(_current_index);
  }
private:
  int            _current_index;
  Aggregate    *_ag;
};

class ConcreteAggregate : public Aggregate
{
public:
  ConcreteAggregate()
  {
    for (int i = 0; i < SIZE; i++)
    {
      object[i] = i + 100;
    }
  }

  virtual MyIterator *CreateIterator()
  {
    return new ContreteIterator(this); //让迭代器 持有一个 集合的 引用 
  }

  virtual Object getItem(int index)
  {
    return object[index];
  }

  virtual int getSize()
  {
    return SIZE;
  }
private:
  Object object[SIZE];
};

void main()
{
  Aggregate * ag = new ConcreteAggregate;

  MyIterator *it = ag->CreateIterator();

  for (; !(it->IsDone()); it->Next())
  {
    cout << it->CurrentItem() << " ";
  }

  delete it;
  delete ag;

  system("pause");
  return;
}