面向对象编程思想-迭代器模式

一、引言

上篇博客中学习了命令模式，是将行为抽象为命令，使得行为请求者和接收者形成低耦合关系。我们知道行为型设计模式关注的是对象职责的分离，今天我们将学习一个新的设计模式，迭代器模式：

二、迭代器模式

定义：提供一种方法顺序访问一个聚合对象中各个元素，而又不暴露该对象的内部显示

下面是迭代器模式结构图：

下面是代码demo：

    //抽象聚合类
    abstract class Aggregate
    {
        public abstract Iterator CreateIterator();
    }
    //具体聚合类
    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); }
        }
    }
    //抽象迭代器类
    abstract class Iterator
    {
        public abstract object First();
        public abstract object Next();
        public abstract bool IsDone();
        public abstract object CurrentItem();

    }
     //具体迭代器类
    class ConcreteIterator : Iterator
    {
        private ConcreteAggregate aggregate;
        private int Current = 0;
        public ConcreteIterator(ConcreteAggregate aggregate)
        {
            this.aggregate = aggregate;
        }

        public override object CurrentItem()
        {
            return aggregate[Current];
        }

        public override object First()
        {
            return aggregate[0];
        }

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

        public override object Next()
        {
            object ret = null;
            Current++;
            if(Current<aggregate.Count)
            {
                ret = aggregate[Current];
            }
            return ret;
        }
    }
     static void Main(string[] args)
        {
            ConcreteAggregate aggregate = new ConcreteAggregate();
            aggregate[0] = "michael";
            aggregate[1] = "jarle";
            aggregate[2] = "cumming";
            aggregate[3] = "andy";
            ConcreteIterator iterator = new ConcreteIterator(aggregate);
            iterator.First();
            while (!iterator.IsDone())
            {
                Console.WriteLine($"{iterator.CurrentItem()},请打卡后再下班");
                iterator.Next();
            }
            Console.Read();
        }

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