设计模式(23)---迭代器模式

定义：

迭代器模式，提供了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表示。

因为迭代器模式的广泛运用，现在高级语言如c#，java等本身已经把这个模式封装在语言当中。例如：c#中的foreach in。

因此此处暂不对迭代器模式做详细的介绍，下面简单讲述在书中看到的一些基础知识：

IEumerator支持对非泛型集合的简单迭代接口。

public interface IEumerator
    {
        object Current { get; }
        bool MoveNext();
        void Reset();
    }

IEnumerable公开枚举数，该枚举数支持在非泛型集合上进行简单迭代。

public interface IEnumerable
    {
        IEumerator GetEnumerator();
    }

简单举例：

IList<string> strList = new List<string>();
            strList.Add("a");
            strList.Add("c");
            strList .Add ("d");

            foreach (string item in strList)
            {
                Console.WriteLine("{0}", item);
            }

基本实现：

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

    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 obj = null;
            current ++;
            if (current < aggregate.Count) obj = aggregate[current];
            return obj;
        }

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

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

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

    class ConcreteAggregate : Aggregate
    {
        private IList<object> items = new List<object>();

        public int Count
        {
            get { return items.Count; }
        }

        public object this[int index]
        {
            get { return items[index]; }
            set { items.Insert(index, value); }
        }

        public override Iterator CreateIterator()
        {
            return new ConcreteIterator(this);
        }
    }

客户端调用：

ConcreteAggregate agg = new ConcreteAggregate();
            agg[0] = "张三";
            agg[1] = "李四";
            agg[2] = "王五";
            agg[3] = "麻子";

            Iterator it = new ConcreteIterator(agg);
            object item = it.First();
            while (!it.IsDone())
            {
                Console.WriteLine("{0}点到名字了", it.CurrentItem());
                it.Next();
            }

项目中实现迭代器的实例：

public class StudentInfo
    {
        public int Id;
        public string Name;

        public StudentInfo(int id, string name)
        {
            this.Id = id;
            this.Name = name;
        }
    }

    public class SchoolInfo : IEnumerable
    {
        public StudentInfo[] stu = new StudentInfo[]
        {
            new StudentInfo(1, "tom"),
            new StudentInfo(2, "jack"),
            new StudentInfo(3, "john")
        };

        public IEnumerator GetEnumerator()
        {
            return this.stu.GetEnumerator();
        }
    }

客户端调用：

SchoolInfo info = new SchoolInfo();
foreach (StudentInfo item in info.stu) Console.WriteLine("Id is {0},Name is {1}", item.Id, item.Name);

结果显示如下：

此外还可以查看Foreach遍历

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