简单的回调

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
   
       class Program
    {
      
        static void Main(string[] args)
        {

            T t = new T();
            t.TT();
            Console.Read();
        }
        
    }

    public class T
    {
        internal delegate string ResolveDelegate(string host);
        public bool resultsDisplayed = false;
        public void TT()
        {
            ResolveDelegate synchMethod = new ResolveDelegate(Resolve);
            AsyncCallback cb = new AsyncCallback(AsyncCustomCallbackMethod);
            // Begin the method's execution...when finished, the callback will be
            // called.
            IAsyncResult ar = synchMethod.BeginInvoke("12", cb, null);
            while (!resultsDisplayed)
            {
                // For the synchronous options, this will never get executed
                // because the results will have been displayed before execution
                // reaches this point.
                System.Threading.Thread.Sleep(100);
            }
        }
        private  void AsyncCustomCallbackMethod(IAsyncResult ar)
        {
            ResolveDelegate synchMethod = (ResolveDelegate)((System.Runtime.Remoting.Messaging.AsyncResult)ar).AsyncDelegate;
            string hostInformation = synchMethod.EndInvoke(ar);
            DisplayResults(hostInformation);
            resultsDisplayed = true;
        }

        private void DisplayResults(string hostInformation)
        {
            Console.WriteLine(hostInformation);
        }

        private static string Resolve(string host)
        {
            Thread.Sleep(5500);
            return host;
        }
    }

}