Xojo Plugin

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. Xojo Plugin

Dim success As Boolean
success = False

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

success = False

Dim mailman As New Chilkat.MailMan

// 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 = True
mailman.MailPort = 995

// Connect to the POP3 server:
success = mailman.Pop3BeginSession()
If (Not success) Then
    System.DebugLog(mailman.LastErrorText)
    Return
End If

// Get the number of messages in the mailbox.
Dim numMessages As Int32
numMessages = mailman.GetMailboxCount()
If (numMessages = 0) Then
    System.DebugLog("No email messages in the POP3 mailbox.")
    Return
End If

Dim taskChain As New Chilkat.TaskChain

// Create async task objects to fetch each email message
// by its sequence number
Dim i As Int32
Dim task As Chilkat.Task

For i = 1 To numMessages

    task = mailman.FetchByMsgnumAsync(i)
    If (mailman.LastMethodSuccess = False) Then
        System.DebugLog(mailman.LastErrorText)
        Return
    End If

    // Append each task to the task chain.
    success = taskChain.Append(task)
    If (Not success) Then
        System.DebugLog(taskChain.LastErrorText)
        Return
    End If

Next

// 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 = True
success = taskChain.Run()
If (Not success) Then
    System.DebugLog(taskChain.LastErrorText)
    Return
End If

// 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 <> True

    // Sleep 100 ms.
    taskChain.SleepMs 100

Wend

// 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
    System.DebugLog("Task did not complete.")
    System.DebugLog("task chain status: " + taskChain.Status)
    Return
End If

Dim email As New Chilkat.Email

Dim numTasks As Int32
numTasks = taskChain.NumTasks
Dim taskIdx As Int32
taskIdx = 0

While (taskIdx < numTasks)

    task = taskChain.GetTask(taskIdx)

    // Load the email object with email downloaded by this task.
    success = email.LoadTaskResult(task)
    If (Not success) Then
        System.DebugLog("Failed to load email object for task.")
    Else
        System.DebugLog(email.From + "; " + email.Subject)
    End If

    taskIdx = taskIdx + 1
Wend