C#之foreach实现探秘

代码 1：
        static void Main(string[] args)
        {
            int[] hs = { 1,2,3,4,5,6,7,8,9};
            foreach (int item in hs)
            {
                Console.WriteLine(item.ToString());
            }

            Console.ReadKey();
        }

代码 2：
        static void Main(string[] args)
        {
            ArrayList ArrLst = new ArrayList();
            ArrLst.AddRange(new string[] { "jack","rose","joy","kristina"});

            foreach (string s in ArrLst)
            {
                Console.WriteLine(s);
            }

            Console.ReadKey();
        }

代码 3：
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ForeachDemo
{
    class Dog
    {
        //构造函数
        public Dog(params string[] dogNames)
        {
            DogNames.AddRange(dogNames);
        }
        //名称字段、属性
        private string name;
        public string Name
        {
            get { return name; }
            set { name = value; }
        }
        //List<string>集合元素数
        public int DogNamesCounts()
        {
            return DogNames.Count;
        }
        public List<string> DogNames = new List<string>();
        //Dog类对象所引器
        public string this[int index]
        {
            get { return DogNames[index];}
            set
            {
                if (index >= DogNames.Count)
                {
                    DogNames.Add(value);
                }
                else
                {
                    DogNames[index] = value;
                }
            }
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Dog D = new Dog("哈士奇","吉娃娃","藏獒","牧羊犬");
            //for循环可以通过所引器访问对象
            //for (int i = 0; i < D.DogNames.Count; i++)
            //{
            //    Console.WriteLine(D[i].ToString());
            //}
            //foreach却不能通过所引器遍历
            foreach (string s in D)
            {
                Console.WriteLine(s);
            }

            Console.ReadKey();
        }
    }
}
    

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

namespace ForeachDemo
{
    class Dog:IEnumerable
    {
        //构造函数
        public Dog(params string[] dogNames)
        {
            DogNames.AddRange(dogNames);
        }
        //名称字段、属性
        private string name;
        public string Name
        {
            get { return name; }
            set { name = value; }
        }
        //List<string>集合元素数
        public int DogNamesCounts()
        {
            return DogNames.Count;
        }
        public List<string> DogNames = new List<string>();
        //Dog类对象所引器
        public string this[int index]
        {
            get { return DogNames[index]; }
            set
            {
                if (index >= DogNames.Count)
                {
                    DogNames.Add(value);
                }
                else
                {
                    DogNames[index] = value;
                }
            }
        }
        //这里需要一个IEnumerator类型的对象返回值(显式实现IEnumerable)
        //IEnumerator IEnumerable.GetEnumerator()
        //{
        //    throw new NotImplementedException();
        //}

        public IEnumerator GetEnumerator()
        {
            return new DogEnumerator(this.DogNames);
        }
    }

    public class DogEnumerator:IEnumerator
    {
        /* 显式实现IEnumerator接口
        object IEnumerator.Current
        {
            get { throw new NotImplementedException(); }
        }

        bool IEnumerator.MoveNext()
        {
            throw new NotImplementedException();
        }

        void IEnumerator.Reset()
        {
            throw new NotImplementedException();
        }*/
        //构造函数
        public DogEnumerator(List<string> paramDogNames)
        {
            this.dogsNames = paramDogNames;
        }

        List<string> dogsNames = new List<string>();

        //枚举器初始索引
        private int index = -1;

        //获取集合中的当前元素
        public object Current
        {
            get
            {
                if (index < 0)
                {
                    return null;
                }
                else
                {
                    return dogsNames[index];
                }
            }
        }
        //判断是否可以将枚举数推进到集合的下一个元素
        public bool MoveNext()
        {
            index += 1;
            if (index >= dogsNames.Count)
            {
                return false;
            }
            else
            {
                return true;
            }
        }
        //将枚举数设置为其初始位置，该位置位于集合中第一个元素之前(索引为-1)
        public void Reset()
        {
            this.index = -1;
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Dog D = new Dog("哈士奇", "吉娃娃", "藏獒", "牧羊犬");

            //for循环可以通过所引器访问对象
            //for (int i = 0; i < D.DogNames.Count; i++)
            //{
            //    Console.WriteLine(D[i].ToString());
            //}

            foreach (string s in D)
            {
                Console.WriteLine(s);
            }
            
            Console.ReadKey();
        }
    }
}