要使用foreach的遍历的类首先要满足的条件
　　1、类要实现公共方法 public IEnumerator GetEnumerator(){}，还可以继承IEnumerable接口来实现这个方法
　　2、类实现了 public IEnumerator GetEnumerator(){}中，要返回一个对象用于遍历的，当然这个对象必须继承IEnumerator 接口
1     class Program
2     {
3         static void Main(string[] args)
4         {
5             Person p = new Person();
6             p[0] = "小明";
7             p[1] = "晓虹";
8             p[2] = "小芳";
9             p[3] = "小龙";
10             for (int i = 0; i < p.Count; i++)
11             {
12                 Console.WriteLine(p[i]);
13             }
14 15             Console.WriteLine("==========================================");
17             foreach (var name in p)
18             {
19                 Console.WriteLine(name);
20             }
21             Console.ReadKey();
22         }
23     }
24
25     internal class Person:IEnumerable
26     {
27         private List<string> listStudent =new List<string>();
28         public int Count {
29             get { return listStudent.Count; }
30         }
31
32         public string this[int index]
33         {
34             get { return listStudent[index]; }
35             set
36             {
37                 if (index>=Count)
38                 {
39                     listStudent.Add(value);
40                 }
41                 else
42                 {
43                     listStudent[index] = value;
44                 }
45             }
46         }
47
48
49
50         public IEnumerator GetEnumerator()
51         {
52            return new PersonIEnumerator(listStudent);
53         }
54     }
55
56     class PersonIEnumerator:IEnumerator
57     {
58         public PersonIEnumerator(List<string> _listName)
59         {
60             listName = _listName;
61         }
62
63         private List<string> listName;
64         private int index = -1;
65
66         public object Current
67         {
68             get {return listName[index]; }
69         }
70
71         public bool MoveNext()
72         {
73             index++;
74             if (index>=listName.Count)
75             {
76                 return false;
77             }
78             else
79             {
80                 return true;
81             }
82         }
83
84         public void Reset()
85         {
86             index = -1;
87         }
88     }