ComponentPro UltimateMail

      Downloading messages headers Asynchronously

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      Use DownloadMessageHeadersAsync methods to asynchronously download headers of a message. These methods download headers of a message asynchronously with execution occurring on a new thread, therefore they allow your next line of code to execute immediately.

      In Task-based Asynchronous programs, the single asynchronous method represents the initiation and completion of an asynchronous operation. You may create the continuation code either explicitly, through methods on the Task class (for example, ContinueWith) or implicitly, by using language support built on top of continuations (for example, await in C#, Await in Visual Basic).

      In .NET 4.5 it is recommended to implement the Task-based Asynchronous Pattern.

      In Event-based Asynchronous programs, the event DownloadMessageHeadersCompleted is raised when the DownloadMessageHeadersAsync method completes. In the event handler method of the DownloadMessageHeadersCompleted, you can check if there were any errors by using the Error property of the event data object.

      The following example demonstrates how to asynchronously download headers of a message:

      Task-based approach

      using System;
      using System.IO;
      using ComponentPro.Net.Mail;
      
      ...
      
      // Create a new instance of the Pop3 class.
      Pop3 client = new Pop3();
      
      // Connect to the server.
      client.Connect("myserver");
      
      // Or you can specify the POP3 port with 
      // client.Connect("myserver", 110); 
       
      // Login to the server.
      client.Authenticate("user", "password");
      
      // ...
      
      MemoryStream stream = new MemoryStream();
      // Download a mail message's headers with sequence number 1 to the specified stream. 
      await client.DownloadMessageHeadersAsync(1, stream, stream);
      
      // ... 
       
      // Load the message for reading.
      MailMessage msg = new MailMessage(stream);
      
      Console.WriteLine("Message downloaded successfully.");
      
      foreach (Header h in msg.Headers)
      {
          Console.WriteLine("Header Name: {0}, Value: {1}", h.Name, h.Raw);
      }
      
      stream.Close();
      
      // Disconnect.
      client.Disconnect();
      

      Event-based approach

      using System;
      using System.ComponentModel;
      using System.IO;
      using ComponentPro;
      using ComponentPro.Net.Mail;
      
      ...
      
      public void DoDownloadMessageHeadersAsync()
      {
          // Create a new instance of the Pop3 class. 
          Pop3 client = new Pop3();
      
          // Connect to the server. 
          client.Connect("myserver");
      
          // Or you can specify the POP3 port with 
          // client.Connect("myserver", 110); 
       
          // Login to the server. 
          client.Authenticate("user", "password");
      
          // ... 
       
          // Register an event handler. 
          client.DownloadMessageHeadersCompleted += client_DownloadMessageHeadersCompleted;
      
          MemoryStream stream = new MemoryStream();
          // Download a mail message's headers with sequence number 1 to the specified stream. 
          client.DownloadMessageHeadersAsync(1, stream, stream);
      
          // ... 
       
          // Disconnect. 
          client.Disconnect();
      }
      
      void client_DownloadMessageHeadersCompleted(object sender, ExtendedAsyncCompletedEventArgs<long> e)
      {
          // Pop3 client = (Pop3)sender; 
          if (e.Error != null)
              Console.WriteLine("Error: " + e.Error.ToString());
          else 
          {
              Stream stream = (Stream) e.UserState;
              // Load the message for reading. 
              MailMessage msg = new MailMessage(stream);
      
              Console.WriteLine("Message downloaded successfully.");
              
              foreach (Header h in msg.Headers)
              {
                  Console.WriteLine("Header Name: {0}, Value: {1}", h.Name, h.Raw);
              }
      
              stream.Close();
          }
      }