IEnumerable接口是非常的简单，只包含一个抽象的方法GetEnumerator()，它返回一个可用于循环访问集合的IEnumerator对象。
IEnumerator是一个真正的集合访问器，没有它，就不能使用foreach语句遍历集合或数组，因为只有IEnumerator对象才能访问集合中的项。
using System;
using System.Collections; // Simple business object.
public class Person
{
public Person(string fName, string lName)
{
this.firstName = fName;
this.lastName = lName;
} public string firstName;
public string lastName;
} // Collection of Person objects. This class
// implements IEnumerable so that it can be used
// with ForEach syntax.
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];
}
} // Implementation for the GetEnumerator method.
IEnumerator IEnumerable.GetEnumerator()
{
return (IEnumerator) GetEnumerator();
} public PeopleEnum GetEnumerator()
{
return new PeopleEnum(_people);
}
} // When you implement IEnumerable, you must also implement IEnumerator.
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 App
{
static void Main()
{
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); }
}