static int TakesAWhile(int data, int ms)        {            Console.WriteLine("TakesAWhile started");            Thread.Sleep(ms);            Console.WriteLine("TakesAWhile completed");            return ++data;        }        public delegate int TakesAWhileDelegate(int data, int ms);        static void Main(string[] args)        {            TakesAWhileDelegate d1 = TakesAWhile;            // polling            IAsyncResult ar = d1.BeginInvoke(1, 3000, null, null);            while (!ar.IsCompleted)            {                // doing something else                Console.Write(".");                Thread.Sleep(500);            }            int result = d1.EndInvoke(ar);            Console.WriteLine("result: {0}", result);            Console.Read();        }

结果：

二：

static int TakesAWhile(int data, int ms)        {            Console.WriteLine("TakesAWhile started");            Thread.Sleep(ms);            Console.WriteLine("TakesAWhile completed");            return ++data;        }        public delegate int TakesAWhileDelegate(int data, int ms);        static void Main(string[] args)        {            TakesAWhileDelegate d1 = TakesAWhile;            // wait handle            IAsyncResult ar = d1.BeginInvoke(1, 3000, null, null);            while (true)            {                Console.Write(".");                if (ar.AsyncWaitHandle.WaitOne(500, false))                {                    Console.WriteLine("Can get the result now");                    break;                }            }            int result = d1.EndInvoke(ar);            Console.WriteLine("result: {0}", result);            Console.Read();        }

结果：

三：

  static int TakesAWhile(int data, int ms)         {
                Console.WriteLine("TakesAWhile started");             Thread.Sleep(ms);             Console.WriteLine("TakesAWhile completed");             return ++data;         }         public delegate int TakesAWhileDelegate(int data, int ms);         static void Main(string[] args)         {
                TakesAWhileDelegate d1 = TakesAWhile;             // async callback             d1.BeginInvoke(1, 3000, TakesAWhileCompleted, d1);             for (int i = 0; i < 100; i++)             {
                    Console.Write(".");                 Thread.Sleep(500);             }             Console.Read();         }         static void TakesAWhileCompleted(IAsyncResult ar)         {
                if (ar == null) throw new ArgumentNullException("ar");             TakesAWhileDelegate d1 = ar.AsyncState as TakesAWhileDelegate;             Trace.Assert(d1 != null, "Invalid object type");             int result = d1.EndInvoke(ar);             Console.WriteLine("result: {0}", result);         }

结果：

四：

static int TakesAWhile(int data, int ms)        {            Console.WriteLine("TakesAWhile started");            Thread.Sleep(ms);            Console.WriteLine("TakesAWhile completed");            return ++data;        }        public delegate int TakesAWhileDelegate(int data, int ms);        static void Main(string[] args)        {            TakesAWhileDelegate d1 = TakesAWhile;            d1.BeginInvoke(1, 3000,            ar =>            {                int result = d1.EndInvoke(ar);                Console.WriteLine("result: {0}", result);            },            null);            for (int i = 0; i < 100; i++)            {                Console.Write(".");                Thread.Sleep(500);            }            Console.Read();        }

结果：同三