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写在前面

异步委托主要用于解决 ThreadPool.QueueUserWorkItem 没有提供获取线程执行完成后的返回值问题。异步委托只能在.Net Framework 框架下使用，.Net Core中会报平台错误，而且使用Task.Result来获取返回值，可以达成同样的目的；本文纯粹是做个验证试验。

代码实现

        static void Main(string[] args){AsyncResultTest();Console.WriteLine("OK");Console.ReadKey();}public static void AsyncResultTest(){var str = "hello";var testOb = new TestOb() { msg = str };Func<TestOb, int> testMethod = Dosomething;//testMethod.BeginInvoke(testOb, Done, testMethod);var asyncResult = testMethod.BeginInvoke(testOb, null, null);var task01 = Task.Factory.StartNew(() =>{Thread.Sleep(1000);testOb.msg = "hello world";Console.WriteLine($"task01 exceuted str is {testOb.msg}");});task01.Wait();var result = testMethod.EndInvoke(asyncResult);Console.WriteLine($"AsyncResultTest finished, result is {result}");}private static int Dosomething(TestOb testOb){Console.WriteLine($"Dosomething:{testOb.msg}");Thread.Sleep(2000);return testOb.msg.Length;}private static void Done(IAsyncResult result){var asyncState = (Func<TestOb, int>)result.AsyncState;var retVal = asyncState.EndInvoke(result);Console.WriteLine($"result is:{retVal}");}class TestOb{public string msg { get; set; }}

执行结果

.Net Core 下实现类似效果的代码：

        public static void TaskReturnValueTest(){var value = "000";var task01 = Task.Factory.StartNew(() =>{value = "111";Thread.Sleep(1000);Console.WriteLine($"task01 exceuted value is {value}.");return "1";});var task02 = Task.Factory.StartNew(() =>{Thread.Sleep(800);value = "222";Console.WriteLine($"task02 exceuted value is {value}.");return "2";});Task.WaitAll(task01, task02);var ret01 = task01.Result;var ret02 = task02.Result;Console.WriteLine($"task01: {ret01}, task02: {ret02}");Console.WriteLine("Ok");}

执行结果： 

总结 

用Task类库的代码实现方式明显更优，更易于理解和维护。