异步委托有返回值 和回调方法 C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Remoting.Messaging;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace 异步委托有返回值 
{
    class Program
    {
        static void Main(string[] args)
        {
            Func<int, int, string> FuncTest = (a, b) =>
           {
               Console.WriteLine("异步线程ID:" + Thread.CurrentThread.ManagedThreadId);
               return (a + b).ToString();
           };
            IAsyncResult rs = FuncTest.BeginInvoke(100, 100, CallBackTest, "传给回调方法的参数");
            Console.WriteLine("主线程ID:" + Thread.CurrentThread.ManagedThreadId);
            Console.ReadKey();
        }
        public static void CallBackTest(IAsyncResult a)
        {
            AsyncResult ia = (AsyncResult)a;//强制转换接口对象
            var ob = (Func<int, int, string>)ia.AsyncDelegate;//获取在其上调用异步调用的委托对象，强转换成委托类型
            string str = ob.EndInvoke(a);//取BeginInvoke返回值。
            Console.WriteLine("回调线程方法ID:" + Thread.CurrentThread.ManagedThreadId + "返回值：" + str.ToString());
            Console.WriteLine(a.AsyncState);//接收传入的参数，也就是BeginInvoke方法倒数第一个参数
        }
    }
}