using System;

using System.Collections;

namespace Test.Iterator.Structural

{

    /// <summary>

​

    /// MainApp startup class for Structural 

​

    /// Iterator Design Pattern.

​

    /// </summary>

​

    public class MainApp

​

    {

        /// <summary>

​

        /// Entry point into console application.

​

        /// </summary>

​

        public static void Main()

        {

            ConcreteAggregate a = new ConcreteAggregate();

            a[0] = "Item A";

            a[1] = "Item B";

            a[2] = "Item C";

            a[3] = "Item D";

            // Create Iterator and provide aggregate

​

            Iterator i = a.CreateIterator();

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

            object item = i.First();

            while (item != null)

            {

                Console.WriteLine(item);

                item = i.Next();

            }

​

        }

    }

    /// <summary>

​

    /// The 'Aggregate' abstract class

​

    /// </summary>

​

    public abstract class Aggregate

​

    {

        public abstract Iterator CreateIterator();

    }

    /// <summary>

​

    /// The 'ConcreteAggregate' class

​

    /// </summary>

​

    public class ConcreteAggregate : Aggregate

​

    {

        private ArrayList _items = new ArrayList();

        public override Iterator CreateIterator()

        {

            return new ConcreteIterator(this);

        }

        // Gets item count

​

        public int Count

        {

            get { return _items.Count; }

        }

        // Indexer

​

        public object this[int index]

        {

            get { return _items[index]; }

            set { _items.Insert(index, value); }

        }

    }

    /// <summary>

​

    /// The 'Iterator' abstract class

​

    /// </summary>

​

    public abstract class Iterator

​

    {

        public abstract object First();

        public abstract object Next();

        public abstract bool IsDone();

        public abstract object CurrentItem();

    }

    /// <summary>

​

    /// The 'ConcreteIterator' class

​

    /// </summary>

​

    public class ConcreteIterator : Iterator

​

    {

        private ConcreteAggregate _aggregate;

        private int _current = 0;

        // Constructor

​

        public ConcreteIterator(ConcreteAggregate aggregate)

        {

            this._aggregate = aggregate;

        }

        // Gets first iteration item

​

        public override object First()

        {

            return _aggregate[0];

        }

        // Gets next iteration item

​

        public override object Next()

        {

            object ret = null;

            if (_current < _aggregate.Count - 1)

            {

                ret = _aggregate[++_current];

            }

            return ret;

        }

        // Gets current iteration item

​

        public override object CurrentItem()

        {

            return _aggregate[_current];

        }

        // Gets whether iterations are complete

​

        public override bool IsDone()

        {

            return _current >= _aggregate.Count;

        }

    }

}