Delphi ActiveX

Async Task Chain

See more Async Examples

Demonstrates how to combine a sequence of asynchronous tasks into a single task chain to be run in a background thread. Delphi ActiveX

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Chilkat_TLB;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Integer;
mailman: TChilkatMailMan;
numMessages: Integer;
taskChain: TChilkatTaskChain;
i: Integer;
task: IChilkatTask;
email: TChilkatEmail;
numTasks: Integer;
taskIdx: Integer;

begin
success := 0;

// This example assumes the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

success := 0;

mailman := TChilkatMailMan.Create(Self);

// Set the POP3 server's hostname
mailman.MailHost := 'pop.example.com';

// Set the POP3 login/password and any other requirements..
mailman.PopUsername := 'myLogin';
mailman.PopPassword := 'myPassword';
mailman.PopSsl := 1;
mailman.MailPort := 995;

// Connect to the POP3 server:
success := mailman.Pop3BeginSession();
if (not success) then
  begin
    Memo1.Lines.Add(mailman.LastErrorText);
    Exit;
  end;

// Get the number of messages in the mailbox.
numMessages := mailman.GetMailboxCount();
if (numMessages = 0) then
  begin
    Memo1.Lines.Add('No email messages in the POP3 mailbox.');
    Exit;
  end;

taskChain := TChilkatTaskChain.Create(Self);

// Create async task objects to fetch each email message
// by its sequence number

for i := 1 to numMessages do
  begin

    task := mailman.FetchByMsgnumAsync(i);
    if (mailman.LastMethodSuccess = 0) then
      begin
        Memo1.Lines.Add(mailman.LastErrorText);
        Exit;
      end;

    // Append each task to the task chain.
    success := taskChain.Append(task);
    if (not success) then
      begin
        Memo1.Lines.Add(taskChain.LastErrorText);
        Exit;
      end;

  end;

// At this point, no tasks have actually started running.
// All we've done so far is to create tasks for the work that will be done
// when the task chain is run.

// Start the task chain running in a background thread.
// Each task is run one after the other (on the same background thread) until all tasks have completed.
// The task chain will stop at the first task that fails.
taskChain.StopOnFailedTask := 1;
success := taskChain.Run();
if (not success) then
  begin
    Memo1.Lines.Add(taskChain.LastErrorText);
    Exit;
  end;

// The application is now free to do anything else
// while the emails are being downloaded

// For this example, we'll simply sleep and periodically
// check to see if the taskchain if finished. 
while taskChain.Finished <> 1 do
  begin

    // Sleep 100 ms.
    taskChain.SleepMs(100);

  end;

// A finished task chain could be one that was canceled, aborted, or truly finished.  

// If the task chain "completed", then it ran to completion.  A "completed" task will
// have a StatusInt equal to 7.   If the task finished, but was not completed, then it must've
// been aborted or canceled:
if (taskChain.StatusInt <> 7) then
  begin
    Memo1.Lines.Add('Task did not complete.');
    Memo1.Lines.Add('task chain status: ' + taskChain.Status);
    Exit;
  end;

email := TChilkatEmail.Create(Self);

numTasks := taskChain.NumTasks;
taskIdx := 0;

while (taskIdx < numTasks) do
  begin

    task := taskChain.GetTask(taskIdx);

    // Load the email object with email downloaded by this task.
    success := email.LoadTaskResult(task);
    if (not success) then
      begin
        Memo1.Lines.Add('Failed to load email object for task.');
      end
    else
      begin
        Memo1.Lines.Add(email.From + '; ' + email.Subject);
      end;

    taskIdx := taskIdx + 1;
  end;
end;