迭代器模式【大话设计模式DEMO】

    abstract class Iterator
    {
        public abstract object First();
        public abstract object Next();
        public abstract bool IsDone();
        public abstract object CurrentItem();
    }

    abstract class Aggregate
    {
        public abstract Iterator CreateIterator();
    }

    class ConcreteIterator : Iterator
    {
        private ConcreteAggregate aggregate;
        private int current = 0;
        public ConcreteIterator(ConcreteAggregate agg)
        {
            this.aggregate = agg;
        }
        public override object First()
        {
            return this.aggregate[0];
        }

        public override object Next()
        {
            object ret = null;
            current++;
            if (current < aggregate.Count)
                ret = aggregate[current];
            return ret;
        }

        public override bool IsDone()
        {
            return current > aggregate.Count ? true : false;
        }

        public override object CurrentItem()
        {
            return this.aggregate[current];
        }
    }

    class ConcreteAggregate : Aggregate
    {
        private IList<object> items = new List<object>();

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

        public int Count
        {
            get { return items.Count; }
        }

        public object this[int index]
        {
            get { return items[index]; }
            set { items.Insert(index, value); }
        }
    }

static void Main()
        {
            ConcreteAggregate a = new ConcreteAggregate();
            a[0] = "a";
            a[1] = "b";
            a[2] = "c";
            a[3] = "d";
            a[4] = "e";
            a[5] = "f";
            Iterator i = new ConcreteIterator(a);
            object item = i.First();
            while(!i.IsDone())
            {
                Console.WriteLine(i.CurrentItem());
                i.Next();
            }
            Console.Read();
        }