迭代器模式

 //自定义聚类
    class DieDaiList : IEnumerable
    {
        private List<object> list = new List<object>() { "n","x","j"};
        public int Length { get { return list.Count; } }
        public object GetElement(int index) { return list[index]; }
        public IEnumerator GetEnumerator()
        {
            return new DieDaiListor(this);
        }
    }

 //对应的自定义迭代器类
    class DieDaiListor : IEnumerator
    {
        private DieDaiList _diedailist;//包含自定义聚类
        private int index;//与索引（因为foreach先执行MoveNext，再执行Current，因此初始化需要设置为-1）
        public DieDaiListor(DieDaiList diedailist)
        {
            _diedailist = diedailist;
            index = -1;//先执行MoveNext，再执行Current，因此这里设置-1
        }
        public object Current
        {
            get
            {
                return _diedailist.GetElement(index);
            }
        }

        public bool MoveNext()
        {
            //++a<0 是先加再比较 而a++<0是先比较a与0再加a  ！！！！！！
            //先执行此，再执行Current
            if (++index< _diedailist.Length)
            {
                return true;
            }
            else
            {
                return false;
            }
        }

        public void Reset()
        {
            index = -1;
        }
    }

 static void Main(string[] args)
        { 
            DieDaiList dd = new DieDaiList();
            foreach (var item in dd)
            {
                Console.WriteLine(item);
            }
            Console.ReadKey();
        }