Iterator Design Pattern

Question

I need an example of iterator pattern. Thanks alot.

Answer 1

Here you go... don't hesitate to ask, if you have some questions.

public class Program
    {
        public static void Main(string[] args)
        {
            // Create 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 = collection.CreateIterator();

            // 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.ReadKey();
        }
    }
    
    // A collection item
    public class Item
    {
        string name;

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

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


    // The 'Aggregate' interface
    public interface IAbstractCollection
    {
        Iterator CreateIterator();
    }

    // The 'ConcreteAggregate' class
    public class Collection : IAbstractCollection
    {
        List<Item> items = new List<Item>();

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

        // Gets item count
        public int Count
        {
            get { return items.Count; }
        }

        // Indexer
        public Item this[int index]
        {
            get { return items[index]; }
            set { items.Add(value); }
        }
    }
    
    // The 'Iterator' interface
    public interface IAbstractIterator
    {
        Item First();
        Item Next();
        bool IsDone { get; }
        Item CurrentItem { get; }
    }

    // The 'ConcreteIterator' class
    public class Iterator : IAbstractIterator
    {
        Collection collection;
        int current = 0;
        int step = 1;

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

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

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

        // Gets or sets stepsize
        public int Step
        {
            get { return step; }
            set { step = value; }
        }

        // Gets current iterator item
        public Item CurrentItem
        {
            get { return collection[current] as Item; }
        }

        // Gets whether iteration is complete
        public bool IsDone
        {
            get { return current >= collection.Count; }
        }
    }