首先是IEnumerable与IEnumerator的定义：
1.IEnumerable接口允许使用foreach循环，包含GetEnumerator()方法，可以迭代集合中的项。
2.IEnumerator接口是一个真正的集合访问器，它包含MoveNext()方法和Current属性，在foreach循环中，如果MoveNext()返回True,则就是用IEnumerator接口的Current属性来获取对象的一个引用，用于foreach循环。
3.如果要迭代一个类，可以使用GetEnumerator(),其返回类型是IEnumerator.
如果要迭代一个类成员，则用IEnumerable.
下面的例子是迭代Person类中的类成员Ages,使用了IEnumerable。第二个例子则是迭代一个类，所以使用了IEnumerator作为返回值。
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Collections;namespace _10_5_5{ public class person { private string name; private int age; public string Name { get { return name; } set { name = value; } } public int Age { get { return age; } set { age = value; } } public person(string PName, int PAge) { Name = PName; Age = PAge; } public static bool operator >(person a, person b) { if (a.Age > b.Age) return true; else return false; } public static bool operator <(person a, person b) { if (a.Age > b.Age) return false; else return true; } public static bool operator >=(person a, person b) { if (a.Age >= b.Age) { return true; } else return false; } public static bool operator <=(person a, person b) { if (a.Age <= b.Age) return true; else return false; } } public class People : DictionaryBase { public IEnumerable Ages//注意是IEnumerable { get { foreach (object person in Dictionary.Values) { yield return (person as person).Age; } } } public person[] GetOldest() { People oldPeople = new People(); person oldPerson = null; person currentPerson; foreach (DictionaryEntry myPeople in Dictionary) { currentPerson = myPeople.Value as person; if (oldPerson == null) { oldPerson = currentPerson; oldPeople.Add(oldPerson); } else { if (currentPerson > oldPerson) { oldPeople.Clear(); oldPeople.Add(currentPerson); oldPerson = currentPerson; } else { if (currentPerson >= oldPerson) { oldPeople.Add(currentPerson); } } } } person[] oldestPeopleArray = new person[oldPeople.Count]; int copyIndex = 0; foreach (DictionaryEntry p in oldPeople) { oldestPeopleArray[copyIndex] = p.Value as person; copyIndex++; } return oldestPeopleArray; } public void Add(person p) { Dictionary.Add(p.Name, p); } public person this[string SName] { get { return (person)Dictionary[SName]; } set { Dictionary[SName] = value; } } } class Program { static void Main(string[] args) { person a = new person("Jack", 11); person b = new person("Json", 10); People s = new People(); s.Add(a); s.Add(b); foreach(int age in s.Ages) { Console.WriteLine("{0}\t", age); } Console.ReadKey(); } }}
下面是自定义的一个迭代器的例子：
Primer.CS
using System;using System.Collections;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace Ch11Ex03_Exam{ public class Primes { private long min; private long max; public Primes():this(2,100) { } public Primes(long minNum,long maxNum) { if(minNum<2) { min=2; }else{ min = minNum; } max = maxNum; } public IEnumerator GetEnumerator()//返回的是IEnumerator { for(long i=min;i<max;i++) { int flag = 1; for(long j=2;j<Math.Sqrt(min);j++) { if(i%j==0) { flag = 0; break; } } if(flag==1) { yield return i; } } } }}
Program.CS:
using System;using System.Collections;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace Ch11Ex03_Exam{ class Program { static void Main(string[] args) { Primes s = new Primes(2, 100); foreach(long i in s) { Console.WriteLine("{0}\t", i); } Console.ReadKey(); } }}