程序代码：

class ColorEnumerator : IEnumerator//定义的枚举类
        {
            string[] Colors;
            int Position = -1;
            public ColorEnumerator(string[] theColors)
            {
                Colors = new string[theColors.Length];
                for (int i = 0; i < theColors.Length;i++ )
                {
                    Colors[i] = theColors[i];
                }
            }
            public object Current
            {
                get
                {
                    if (Position==-1)
                    {
                        throw new InvalidOperationException();
                    }
                    if (Position==Colors.Length)
                    {
                        throw new InvalidOperationException();
                    }
                    return Colors[Position];
                }

            }
            public bool MoveNext()
            {
                if (Position < Colors.Length - 1)
                {
                    Position++;
                    return true;
                }
                else
                    return false;
            }
            public void Reset()
            {
                Position = -1;
            }
        }
        class MyColors : IEnumerable
        {
            string[] Colors = { "red", "yellow", "blue" };
            public IEnumerator GetEnumerator()
            {
                return new ColorEnumerator(Colors);
            }
        }

 static void Main(string[] args)
        {
            {
                MyColors my = new MyColors();
                foreach (string color in my)//在这里，使用foreach为什么会调用MyColors类中的GetEnumerator方法啊？而进入ColorEnumerator类中方法的调用顺序又是怎么一回事啊？
                {
                    Console.WriteLine(color);
                }
                Console.ReadKey();
              }              
         }