VB.NET

Async Methods Returning an Object

See more Async Examples

Demonstrates how to call an asynchronous method that returns an object. This example reads email from a POP3 server using the Async versions of the Chilkat methods. VB.NET

Dim success As Boolean = 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:
Dim task As Chilkat.Task = mailman.Pop3BeginSessionAsync()
If (mailman.LastMethodSuccess = False) Then
    Debug.WriteLine(mailman.LastErrorText)
    Exit Sub
End If


' Start the background task.
success = task.Run()
If (Not success) Then
    Debug.WriteLine(task.LastErrorText)

    Exit Sub
End If

' Wait for the POP3 connect task to finish.
' The True/False returned by Wait applies to the Wait method call, not the task.
Dim maxWaitMs As Integer = 30000
success = task.Wait(maxWaitMs)
If (Not success Or (task.StatusInt <> 7) Or (task.TaskSuccess <> True)) Then
    If (Not success) Then
        ' The task.LastErrorText applies to the Wait method call.
        Debug.WriteLine(task.LastErrorText)
    Else
        ' The ResultErrorText applies to the underlying task method call (i.e. the Pop3BeginSession)
        Debug.WriteLine(task.Status)
        Debug.WriteLine(task.ResultErrorText)
    End If


    Exit Sub
End If




' Get the number of messages in the mailbox.
task = mailman.GetMailboxCountAsync()

' To keep the example short, we'll skip handling failures.
' The failures would be handled in the same way as shown above.

success = task.Run()
success = task.Wait(maxWaitMs)
Dim numMessages As Integer = task.GetResultInt()

If (numMessages = 0) Then
    Exit Sub
End If


Dim email As New Chilkat.Email

Dim i As Integer
For i = 1 To numMessages

    task = mailman.FetchByMsgnumAsync(i)
    If (mailman.LastMethodSuccess = False) Then
        Debug.WriteLine(mailman.LastErrorText)
        Exit Sub
    End If


    success = task.Run()
    success = task.Wait(maxWaitMs)
    If (Not success Or (task.StatusInt <> 7) Or (task.TaskSuccess <> True)) Then
        If (Not success) Then
            ' The task.LastErrorText applies to the Wait method call.
            Debug.WriteLine(task.LastErrorText)
        Else
            ' The ResultErrorText applies to the underlying task method call (i.e. the FetchByMsgnum)
            Debug.WriteLine(task.Status)
            Debug.WriteLine(task.ResultErrorText)
        End If


        Exit Sub
    End If


    ' Each Chilkat object that can be a return value of an asynchronous task will
    ' have a method named LoadTaskResult.  The object returned in the underlying
    ' asynchronous method call is retrieved by calling LoadTaskResult. 

    ' To say it another way: The application will provide a pre-existing object of
    ' the desired return type (in this case it is an email object).  This object is
    ' loaded by calling LoadTaskResult.  

    success = email.LoadTaskResult(task)


    If (Not success) Then
        Debug.WriteLine(email.LastErrorText)
        Exit Sub
    Else
        Debug.WriteLine(email.From & ": " & email.Subject & vbLf)
    End If


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