迭代器模式

标签：设计模式   迭代器模式   

UML类图：

实例实现代码：

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

    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); }
        }
    }

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

    class ConcreteIterator : Iterator
    {
        private ConcreteAggregate aggregate;
        private int current = 0;

        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 object CurrentItem()
        {
            return aggregate[current];
        }

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

    }

    class ConcreteIteratorDesc : Iterator
    {
        private ConcreteAggregate aggregate;
        private int current = 0;

        public ConcreteIteratorDesc(ConcreteAggregate aggregate)
        {
            this.aggregate = aggregate;
            current = aggregate.Count - 1;
        }

        public override object First()
        {
            return aggregate[aggregate.Count - 1];
        }

        public override object Next()
        {
            object ret = null;
            current--;
            if (current >= 0)
            {
                ret = aggregate[current];
            }

            return ret;
        }

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

        public override bool IsDone()
        {
            return current < 0 ? true : false;
        }

    }

客户端实现：

        static void Main(string[] args)
        {
            ConcreteAggregate a = new ConcreteAggregate();

            a[0] = "大鸟";
            a[1] = "小菜";
            a[2] = "行李";
            a[3] = "老外";
            a[4] = "公交内部员工";
            a[5] = "小偷";

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

            Console.Read();
        }

说明：

提供一种方法顺序访问一个聚合对象中各个元素，而又不需要暴露该对象的内部表示。

在Cocoa Touch框架中使用迭代器模式：

- iOS开发中的“枚举”就是我们的迭代，基础框架中的NSEnumerator类实现了迭代器模式。抽象NSEnumerator类的私有具体子类返回枚举器对象，能够顺序遍历各种集合---数组，集合，字典，把这些集合中的对象返回给客户端。

- 基于块的枚举，NSArray,NSDictionary,NSSet对象中引入了新方法，用于基于块的枚举，例如- (void)enumerateObjectsUsingBlock:(void (^)(id obj, NSUInteger idx, BOOL *stop))block;

- 快速枚举。

参考资料

-《Objective-C编程之道》

迭代器模式

标签：设计模式   迭代器模式   

原文地址：http://blog.csdn.net/junjun150013652/article/details/45502107