二十二.迭代器模式

迭代器模式：

       提供一種方法順序訪問一個彙總對象中的各個元素，而又不暴露該對象的內部表示。

       C#/java中的foreach就是迭代器的使用。

 

.net

       IEumerator支援對非泛型集合的簡單迭代介面。

       如foreach(string i in Str){print i}

       就是：   

       IEnumerator<string>e=Str.GetEnumerator();

       While(e.MoveNext())

       {    

              Printe.Current;

}

 

Demo:

       //迭代器抽象類別

   abstract class Iterator

    {

       public abstract object First();

       public abstract object Next();

       public abstract bool IsDone();

       public abstract object CurrentItem();

    }

   //具體迭代器

   class ConcreteIterator : Iterator

    {

       private ConcreteAggregate aggregate;

       private int current = 0;

 

       public ConcreteIterator(ConcreteAggregate aggregate)

       {

           this.aggregate = aggregate;

       }

 

       public override object First()

       {

            return aggregate;

       }

 

       public override object Next()

       {

           object ret = null;

           current++;

           if (current < aggregate.Count)

           {

                ret=aggregate[current];

           }

            return ret;

       }

       public override bool IsDone()

       {

           return current >= aggregate.Count ? true : false;

       }

       public override object CurrentItem()

       {

           return aggregate[current];

       }

}

 

 

       //聚集抽象類別

    abstract class Aggregate

    {

       public abstract Iterator CreateIterator();

    }

   //具體聚集類

   class ConcreteAggregate : Aggregate

    {

       private IList<object> items=new List<object>();

       public override Iterator CreateIterator()

       {

           return new ConcreteIterator(this);

       }

       public int Count//返回聚集總數

       {

           get { return items.Count; }

       }

       publicobject this[int index]//聲明一個索引器

       {

           get { return items[index]; }

           set { items.Insert(index,value ); }

       }

}

 

 

       class Program

    {

       static void Main(string[] args)

       {

           ConcreteAggregate a = new ConcreteAggregate();

           a[0] = "大鳥";

           a[1] = "大鳥1";

            a[2] = "大鳥2";

           a[3] = "大鳥3";

 

           Iterator i = new ConcreteIterator(a);

           //object ittem = i.First();

           while (!i.IsDone())

           {

                Console.WriteLine("{0}請買票。",i.CurrentItem());

               i.Next();

           }

           Console.ReadKey();

       }

    }