Iterator

// Iterator pattern -- Real World example

using System;
using System.Collections;

namespace DoFactory.GangOfFour.Iterator.RealWorld
{

  // MainApp test application

  class MainApp
  {
    static void Main()
    {
      // Build a collection
      Collection collection = new Collection();
      collection[0] = new Item("Item 0");
      collection[1] = new Item("Item 1");
      collection[2] = new Item("Item 2");
      collection[3] = new Item("Item 3");
      collection[4] = new Item("Item 4");
      collection[5] = new Item("Item 5");
      collection[6] = new Item("Item 6");
      collection[7] = new Item("Item 7");
      collection[8] = new Item("Item 8");

      // Create iterator
      Iterator iterator = new Iterator(collection);

      // Skip every other item
      iterator.Step = 2;

      Console.WriteLine("Iterating over collection:");

      for(Item item = iterator.First();
        !iterator.IsDone; item = iterator.Next())
      {
        Console.WriteLine(item.Name);
      }

      // Wait for user
      Console.Read();
    }
  }

  class Item
  {
    string name;

    // Constructor
    public Item(string name)
    {
      this.name = name;
    }

    // Property
    public string Name
    {
      get{ return name; }
    }
  }

  // "Aggregate"

  interface IAbstractCollection
  {
    Iterator CreateIterator();
  }

  // "ConcreteAggregate"

  class Collection : IAbstractCollection
  {
    private ArrayList items = new ArrayList();

    public Iterator CreateIterator()
    {
      return new Iterator(this);
    }

    // Property
    public int Count
    {
      get{ return items.Count; }
    }
    
    // Indexer
    public object this[int index]
    {
      get{ return items[index]; }
      set{ items.Add(value); }
    }
  }

  // "Iterator"

  interface IAbstractIterator
  {
    Item First();
    Item Next();
    bool IsDone{ get; }
    Item CurrentItem{ get; }
  }

  // "ConcreteIterator"

  class Iterator : IAbstractIterator
  {
    private Collection collection;
    private int current = 0;
    private int step = 1;

    // Constructor
    public Iterator(Collection collection)
    {
      this.collection = collection;
    }

    public Item First()
    {
      current = 0;
      return collection[current] as Item;
    }

    public Item Next()
    {
      current += step;
      if (!IsDone)
        return collection[current] as Item;
      else
        return null;
    }

    // Properties
    public int Step
    {
      get{ return step; }
      set{ step = value; }
    }

    public Item CurrentItem
    {
      get
      {
        return collection[current] as Item;
      }
    }

    public bool IsDone
    {
      get
      {
        return current >= collection.Count ? true : false;
      }
    }
  }
}