Detailed Explanation of C Asynchronous Call Example

This article example shares the specific code of C # asynchronous call for everyone's reference, the specific content is as follows

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Threading.Tasks;

namespace AsyncAppTest
{
  //// Detailed explanation of asynchronous call example   
  ///  No. 1 1 Step: Define delegates; The return value of this delegate, the parameter type must be the same as the asynchronous method to be called 1 To; 
  ///
  public delegate Task<string> AsyncSendMail(string rece, string copyer, string subj, string body);
  
  class DelegateTest
  {
    // Defining delegate variables 
    AsyncSendMail sendMail = null; 
    
    // Callback method of asynchronous method 
    // Callback methods must have a callback method of type  IAsyncResult Parameters of, 
    // To get the start asynchronous  BeginInvoke The call result of 
    void BackCall(IAsyncResult parameter)
    { 
      //parameter.IsCompleted Used to judge whether the asynchronous method has been called completely; 
      if(parameter.IsCompleted)
      {  
        // Pass EndInvoke Method to get the return result of an asynchronous method (type and result of an asynchronous method 1 To)       
        Task<string> message = sendMail.EndInvoke(parameter);
        Console.Write(string.Format(" Callback complete, return value: {0}", message.Result));
      }
      else
      {
        Console.Write(" Incomplete call ");
      }
    }

    public string AsyncSendMailHandler( string rece, string copyer, string sub, string body)
    { 
      //WcfTest.MailServiceClient  Is on the server Wcf Service, which is the asynchronous method to be called in this example 
      WcfTest.MailServiceClient sc = new WcfTest.MailServiceClient();
      
      // Associating asynchronous methods with delegates 
      sendMail = new AsyncSendMail(sc.SendEmailAsync); 
      string s = null;
      // The following BeginInvoke Method is called by setting the  SendEmailAsync Parameters of the, BackCall Is a callback method, s The role here is not understood, 
      // However, the parameters cannot be omitted 
      //  Asynchronous is relative to the thread on which the delegate instance is threaded, which in this example refers to sendMail And sc.MailServiceClient No 1 Threads; 
      sendMail.BeginInvoke(rece, copyer, sub, body, BackCall, s);      
      return s;
    }
    }
    
  class Program
  {    
    static void Main(string[] args)
    {      
      DelegateTest test = new DelegateTest();
      test.EventCompleteHandle("gqpeng@cmhit.com", null, " Test mail ", " Test mail ");
      Console.Write(" The above is the asynchronous start call ");
      Console.Read(); 
    }
  } 
}

Another: The following is the difference between Invoke and BeginInvoke.

Control. Invoke method (Delegate): Executes the specified delegate on the thread that owns the underlying window handle for this control.

Control. BeginInvoke method (Delegate): Executes the specified delegate asynchronously on the thread on which the control's underlying handle was created.