public static Task<double> GetValueAsync(double num1, double num2)

        {

            return Task.Run(() =>

            {

                for (int i = ; i < ; i++)

                {

                    Thread.Sleep();

                    num1 = num1 + num2;

                    Console.WriteLine("num:{0}", i);

                }

                return num1;

            });

        }

        public static async void DisplayValue()

        {

            double result = await GetValueAsync(1234.5, 1.01);//此处会开新线程处理GetValueAsync任务，然后方法马上返回

            //这之后的所有代码都会被封装成委托，在GetValueAsync任务完成时调用

            System.Diagnostics.Debug.WriteLine("Value is : " + result);

        }

  /// <summary>

        ///  Task<string> 表示一个有返回值异步操作

        /// </summary>

        /// <param name="name"></param>

        /// <returns></returns>

        public static async Task<string> IssuerAsync(string name)

        {

            var str = "";

            var task = Task.Run(() =>

            {

                Thread.Sleep();

                Console.WriteLine("task name:{0}", name);

                str = "my name is " + name;

            });

            //等待任务执行

            await task;

            return str;

        }

   Task<string> task = AsyncAwaitTempte.IssuerAsync("liuyl");

            Console.WriteLine("count value:");

            for (int i = ; i < ; i++)

            {

                Console.WriteLine("task:{0}", i);

                Thread.Sleep();

            }

             Console.WriteLine("task value:{0}", task.Result);

   /// <summary>

        ///  Task<string> 表示一个有返回值异步操作

        /// </summary>

        /// <param name="name"></param>

        /// <returns></returns>

        public static async Task<string> IssuerAsync(string name)

        {

            string str = "";

            var task = new Task(() =>

            {

                for (int i = ; i < ; i++)

                {

                    Thread.Sleep();

                    Console.WriteLine("task name:{0}", name);

                }

                str = "my name is " + name;

            });

            task.Start();

            //task.Wait(); 与   await task ; 不能同时使用

            //等待任务执行

            await task ;

            return str;

        }