VB.NET

Using IMAP IDLE to Wait for Updates

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

Dim success As Boolean = False

Dim imap As New Chilkat.Imap

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

' Select an IMAP mailbox
success = imap.SelectMailbox("INBOX")
If (success <> True) Then
    Debug.WriteLine(imap.LastErrorText)
    Exit Sub
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
    Debug.WriteLine(imap.LastErrorText)
    Exit Sub
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
    Debug.WriteLine(imap.LastErrorText)
    Exit Sub
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
    Debug.WriteLine(imap.LastErrorText)
    Exit Sub
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