B4X

Using IMAP IDLE to Wait for Updates

This example demonstrates how to use the IMAP IDLE functionality in Chilkat. B4X

Dim success As Boolean = False

Dim imap As ChilkatImap
imap.Initialize("imap")

'  ....
'  ....
'  ....

'  Select an IMAP mailbox
success = imap.SelectMailbox("INBOX")
If success <> True Then
    Log(imap.LastErrorText)
    Return
End If


'  After a mailbox has been selected, IDLE may begin.
'  Idling tells the IMAP server to push unsolicited updates for the selected
'  mailbox to the connected client (which is your application).
success = imap.IdleStart
If success <> True Then
    Log(imap.LastErrorText)
    Return
End If


'  Once idling has started, your code still has to periodically check to see
'  if any updates have arrived.  However, this is significantly different
'  then what normally occurs when checking email.  The IdleCheck does NOT
'  send a message to the IMAP server.  It simply checks the connection to see
'  if any data has arrived.  If so, it can be consumed and the client (your app)
'  can react appropriately.  

'  Note: It is recommended that idling only run for a max of 20 minutes before stopping and
'  re-starting the IDLE.  This is to maintain a minimum low level of activity so that 
'  the IMAP server does not disconnect (which it may do if it considers the connection to 
'  be truly inactive, i.e. forgotten).

'  To check the connection for IDLE updates, call IdleCheck.  The 1st argument indicates how
'  long we're willing to wait. We'll wait 1 millisecond:
Dim idleResultXml As String
idleResultXml = imap.IdleCheck(1)
If imap.LastMethodSuccess <> True Then
    Log(imap.LastErrorText)
    Return
End If


'  See the online reference documentation for details regarding the XML that is returned.
'  Your application code would parse the XML to determine what action to take.
'  If the XML contains "<idle></idle>", then no updates are available and your application
'  would call IdleCheck again at some point in the future.

'  If updates are available, the IDLE must be terminated by calling IdleDone, like this:
success = imap.IdleDone
If success <> True Then
    Log(imap.LastErrorText)
    Return
End If


'  Once the IDLE is terminated, your application can make calls to fetch email, etc.
'  Any attempt to communicate with the IMAP server prior to terminating the IDLE will
'  result in failure.

'  IMPORTANT: Please realize that your application code will be structured differently than shown here.
'  The call to IdleCheck will likely be in a function/procedure that is periodically called
'  after the IdleStart has been called from some other location in your app.