迭代器（Iterator）模式

/*
*迭代器（Iterator）模式：提供货一种方法顺序反问一个聚合对象中的各个元素。
*/

    ConcreteAggregate a = new ConcreteAggregate();
            a[0] = "A";
            a[1] = "B";
            a[2] = "C";
            a[3] = "D";

            Iterator i = new ConcreteIterator(a);

            object item = i.First();
            while (!i.IsDone())
            {
                Console.WriteLine("{0} 请买车票！ ", i.CurrentItem());
                i.Next();
            }

            Console.ReadLine();

    /// <summary>
    /// 迭代器（Iterator） 抽象类
    /// </summary>
    abstract class Iterator
    {
        public abstract object First();
        public abstract object Next();
        public abstract bool IsDone();
        public abstract object CurrentItem();
    } 

    /// <summary>
    /// Aggregate 集聚抽象类
    /// </summary>
    abstract class Aggregate
    {
        public abstract Iterator CreateIterator();
    }

    /// <summary>
    /// ConcreteIterator 具体迭代器
    /// </summary>
    class ConcreteIterator : Iterator
    {
        //创建一个具体集聚类对象
        private ConcreteAggregate aggregate;
        private int current = 0;

        //初始化具体集聚类传入对象
        public ConcreteIterator(ConcreteAggregate aggregate)
        {
            this.aggregate = aggregate;
        }
        public override object First()
        {
            return 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 aggregate[current];
        }
    }

    /// <summary>
    /// 具体 集聚类
    /// </summary>
    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; } }

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

 在.net中IEumerator 已经为你准备好了接口，你只要去实现它就好。

 其实就一个  foreach 循环的底层方法。 封装后就是foreach  遍历集合

    public interface IEumerator
    {
        object Current
        { get; }
        bool MoveNext();
        void Reset(); 
    }

    public interface IEnumerable
    {
        IEumerator GetEnumerator();
    }