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;       }     }   } }