实现自定义集合的可枚举类型（IEnumerable）和枚举数（IEnumerator ）

下面的代码示例演示如何实现自定义集合的 IEnumerable 和 IEnumerator 接口：

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

 namespace ConsoleApplication1
 {
     public class Person
     {
         public Person(string fName, string lName)
         {
             this.firstName = fName;
             this.lastName = lName;
         }

         public string firstName;
         public string lastName;
     }

     public class People : IEnumerable
     {
         private Person[] _people;
         public People(Person[] pArray)
         {
             _people = new Person[pArray.Length];

             for (int i = ; i < pArray.Length; i++)
             {
                 _people[i] = pArray[i];
             }
         }

         IEnumerator IEnumerable.GetEnumerator()
         {
             return (IEnumerator)GetEnumerator();
         }

         public PeopleEnum GetEnumerator()
         {
             return new PeopleEnum(_people);
         }
     }

     public class PeopleEnum : IEnumerator
     {
         public Person[] _people;

         // Enumerators are positioned before the first element
         // until the first MoveNext() call.
         int position = -;

         public PeopleEnum(Person[] list)
         {
             _people = list;
         }

         public bool MoveNext()
         {
             position++;
             return (position < _people.Length);
         }

         public void Reset()
         {
             position = -;
         }

         object IEnumerator.Current
         {
             get
             {
                 return Current;
             }
         }

         public Person Current
         {
             get
             {
                 try
                 {
                     return _people[position];
                 }
                 catch (IndexOutOfRangeException)
                 {
                     throw new InvalidOperationException();
                 }
             }
         }
     }

     class Program
     {
         static void Main(string[] args)
         {
             Person[] peopleArray = new Person[]
             {
                 new Person("John", "Smith"),
                 new Person("Jim", "Johnson"),
                 new Person("Sue", "Rabon"),
             };

             People peopleList = new People(peopleArray);
             foreach (Person p in peopleList)
                 Console.WriteLine(p.firstName + " " + p.lastName);
         }
     }
 }

可枚举类型 → 实现IEnumerable接口，可以不需要直接实现这个接口，但必须有个GetEnumerator方法，返回值类型必须为IEnumerator类型，也就是第四点最后一段代码中接口注释的那种写法！

枚举数 → 实现IEnumerator接口，实现全部方法，首先是调用GetEnumerator返回一个类型为IEnumerator的枚举数，然后编译器会隐式的调用实现IEnumerator类中的方法和属性！

总结：所以实现foreach遍历，必须达到上面的两种条件才能进行遍历对象，他们可以写在一起也可以分开，最好是分开，进行职责分离，一个类干一件事总归是好事！也满足面向对象的单一指责设计原则。