設計模式 之 迭代器模式

迭代器提供了一種方法順序訪問一個彙總對象，而不暴露對象的內部細節  。net中的foreach就是典型的迭代器模式

圖示：

代碼：

  車上售票員對乘客售票

  class Program    {        static void Main(string[] args)        {            ConcreteAggregate a = new ConcreteAggregate();            a[0] = "大鳥";            a[1] = "xiao菜";            a[2] = "行李";            a[3] = "老外";            a[4] = "內部員工";            a[5] = "小偷";            Iterator i = new ConcreteIterator(a);            object item = i.First();            while (!i.IsDone()) {                Console.WriteLine("{0}請買車票！",i.CurrentItem());                i.Next();            }            Console.Read();        }    }    //抽象迭代器類    abstract class Iterator {        public abstract object First();        public abstract object Next();        public abstract bool IsDone();        public abstract object CurrentItem();    }    //彙總抽象類別    abstract class Aggregate {        public abstract Iterator createIterator(); //建立迭代器    }    //具體迭代器類    class ConcreteIterator : Iterator {        private ConcreteAggregate aggregate;        private int current = 0;        public ConcreteIterator(ConcreteAggregate aggregate) {            this.aggregate = aggregate;        }        public override object First()        {            //throw new NotImplementedException();            return aggregate[0];        }        public override object Next()        {            //throw new NotImplementedException();            object ret = null;            current++;            if (current < aggregate.Count) {                ret = aggregate[current];            }            return ret;        }        public override bool IsDone()        {            //throw new NotImplementedException();            return current >= aggregate.Count ? true : false;        }        public override object CurrentItem()        {            //throw new NotImplementedException();            return aggregate[current];        }           }    class ConcreteAggregate : Aggregate {         //聲明一個IList 泛型變數 用來存放彙總對象        private IList<object> items=new List<object>();        public override Iterator createIterator()        {            //throw new NotImplementedException();            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); }        }    }

運行結果：