C# yield return 返回枚举器

1.举例

 

-------------类定义--------------

    public class GameMoves
    {
        private int move = 0;
        const int MaxMoves = 9;
        private System.Collections.IEnumerator cross;
        private System.Collections.IEnumerator circle;

        public GameMoves()
        {
            cross = Cross();
            circle = Circle();
        }

        public System.Collections.IEnumerator Cross()
        {
            while (true)
            {
                Console.WriteLine("Cross move {0}", move);
                if (++move > MaxMoves)
                {
                    yield break;
                }
                yield return circle;
            }
        }

        public System.Collections.IEnumerator Circle()
        {
            while (true)
            {
                Console.WriteLine("Circle move {0}", move);
                if (++move > MaxMoves)
                {
                    yield break;
                }
                yield return cross;
            }
        }
    }

-------------测试代码--------------

        private void button1_Click(object sender, EventArgs e)
        {
            var game = new GameMoves();
            System.Collections.IEnumerator enumerator = game.Cross();
            while (enumerator.MoveNext())
            {

                //这句代码的作用是交替执行，取消该行，将不会交替执行
                enumerator = enumerator.Current as System.Collections.IEnumerator;
            }
        }

--------------测试结果----------------

分析：

在while循环中，调用enumerator.MoveNext()。第一次调用enumerator.MoveNext()时，会调用Cross()方法,
Cross()方法是用yield语句返回另一个枚举器,这样下次将会执行Circle()方法,两个方法交替执行，直到
move>9后停止