設計模式之迭代器模式

說起迭代器，大家一定不陌生，經常使用的foreach in 這種迴圈就是，C#語言已經內置化了迭代器模式，主要是支持對非泛型集合的簡單迭代介面IEumerator和公開枚舉數IEnumerable。雖然內置了，但是這種模式也有我們學習的必要性。

代碼如下

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace 設計模式之迭代器模式
{
    public abstract class Iterator//抽象迭代器
    {
        public abstract object First();
        public abstract object Next();
        public abstract object Current();
        public abstract bool IsMax();
    }
    public abstract class Aggregate//抽象被迭代的對象
    {
        public abstract Iterator CreateIterator();
    }
    public class AIterator : Iterator//具體的迭代器
    {
        public AAggregate listA = new AAggregate();//存放被迭代的對象
        private int current=0;
        public AIterator(AAggregate a)//初始化時綁定被迭代的對象
        {
            listA = a;
        }
        public override object First()//獲得第一個迭代的對象
        {
            return listA[0];
        }
        public override object Next()//獲得當前對象的下一個對象
        {
            current++;
            if (current < listA.Count())
            {
                return listA[current];
            }
            else
            {
                return null;
            }
        }
        public override object Current()//獲得當前對象
        {
            return listA[current];
        }
        public override bool IsMax()
        {
            return current == listA.Count() ? true : false;
        }
    }
    public class AAggregate : Aggregate//具體的被迭代對象，迭代方向是正向。
    {
        public IList<object> lists = new List<object>();
        public override Iterator CreateIterator()//創被迭代對象的造迭代器
        {
            return new AIterator(this);
        }
        public int Count()//獲得被迭代對象的個數
        {
            return lists.Count;
        }
        public object this[int index]//索引器
        {
            get
            {
                return lists[index];
            }
            set
            {
                lists.Insert(index, value);
            }
        }
    }
    public class BIterator : Iterator
    {
        public AAggregate blist = new AAggregate();
        private int current=0;
        public BIterator(AAggregate a)
        {
            blist = a;
            current = a.Count() - 1;
        }
        public override object Current()
        {
            return blist[current];
        }
        public override object First()
        {
            return blist[blist.Count()-1];
        }
        public override bool IsMax()
        {
            return current<0? true : false;
        }
        public override object Next()
        {
            current--;
            if(current>=0)
            {
                return blist[current];
            }
            return null;
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            AAggregate a = new AAggregate();
            a[0] = "你好";
            a[1] = "你真的好嗎？";
            a[2] = "你他媽有病啊！老子很好";
            AIterator b = new AIterator(a);
            while(!b.IsMax())
            {
                Console.WriteLine(b.Current());
                b.Next();
            }
            Console.WriteLine();
            BIterator c = new BIterator(a);
            while(!c.IsMax())
            {
                Console.WriteLine(c.Current());
                c.Next();
            }
            Console.Read();
        }
    }
}

運行結果：