Foreach 原理

 1  public class Person
 2     {
 3         private string[] friends = { "asf", "ewrqwe", "ddd", "eeee" };
 4         public string name { get; set; }
 5 
 6         public int age { get; set; }
 7         //这是第一种方法 
 8         public IEnumerable ForEach()
 9         {
10             for (int i = 0; i < friends.Length; i++)
11             {
12                 yield return friends[i];
13             }
14         }
15 }

调用

 1  class Program
 2     {
 3         static void Main(string[] args)
 4         {
 5             Person p = new Person();
 6            
 7             foreach (var item in p.ForEach())
 8             {
 9                 Console.WriteLine(item);
10             }
11          
12             Console.Read();
13         }
14     }

第二种方法

  class Program
    {
        static void Main(string[] args)
        {
            Person p = new Person();
           
            foreach (var item in p)
            {
                Console.WriteLine(item);
            }
         
            Console.Read();
        }
    }

    public class Person
    {
        private string[] friends = { "asf", "ewrqwe", "ddd", "eeee" };
        public string name { get; set; }

        public int age { get; set; }

        //这是第二种
        ////当返回值类型是IEnumerator时，
        //编译器帮我们生成了一个“枚举器”类，
        //即：一个实现了IEnumerator接口的类型。
        public IEnumerator GetEnumerator()
        {
            for (int i = 0; i < friends.Length; i++)
            {
                yield return friends[i];
            }
        }
    }

View Code

第三种方法自己生产枚举器

 1  class Program
 2     {
 3         static void Main(string[] args)
 4         {
 5             Person p = new Person();
 6            
 7             foreach (var item in p)
 8             {
 9                 Console.WriteLine(item);
10             }
11          
12             Console.Read();
13         }
14     }
15 
16     public class Person
17     {
18         private string[] friends = { "asf", "ewrqwe", "ddd", "eeee" };
19         public string name { get; set; }
20 
21         public int age { get; set; }
22 
23         //这是第二种
24         ////当返回值类型是IEnumerator时，
25         //编译器帮我们生成了一个“枚举器”类，
26         //即：一个实现了IEnumerator接口的类型。
27         public IEnumerator GetEnumerator()
28         {
29             return new PersonEnumerator(friends);
30         }
31     }
32 
33     
34     //枚举器
35     public class PersonEnumerator : IEnumerator
36     {
37         private string[] frends;
38         //使用构造函数 传值
39         public PersonEnumerator(string[] fs)
40         {
41             frends = fs;
42         }
43         private int index = -1;
44 
45 
46         public object Current
47         {
48             get
49             {
50                 if (index >= 0 && index < frends.Length)
51                 {
52                     return frends[index];
53                 }
54                 else
55                 {
56                     throw new NotImplementedException();
57                 }
58             }
59         }
60 
61         public bool MoveNext()
62         {
63             if (index + 1 < frends.Length)
64             {
65                 index++;
66                 return true;
67             }
68             return false;
69         }
70 
71         public void Reset()
72         {
73             index = -1;
74 
75         }
76 
77        
78     }

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