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 = ;
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", );
person b = new person("Json", );
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(,)
{ }
public Primes(long minNum,long maxNum)
{
if(minNum<)
{
min=;
}else{
min = minNum;
}
max = maxNum;
}
public IEnumerator GetEnumerator()//返回的是IEnumerator
{
for(long i=min;i<max;i++)
{
int flag = ;
for(long j=;j<Math.Sqrt(min);j++)
{
if(i%j==)
{
flag = ;
break;
}
}
if(flag==)
{
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(, );
foreach(long i in s)
{
Console.WriteLine("{0}\t", i);
}
Console.ReadKey();
}
}
}