Re: Problem understanding asynchronous processes

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From: Larry Daugherty (Larry.NoSpam.Daugherty_at_verizon.net)
Date: 03/05/05 

Date: Sat, 5 Mar 2005 11:35:48 -0800

I think your issue is more in the sphere of ActiveX than of Access.

HTH 

-- 
-Larry-
--
"Browser" <Browser@discussions.microsoft.com> wrote in message
news:D8BB3C51-6548-4FA4-8C0E-7F066EC97D92@microsoft.com...
> Hello,
>
> I'm new to VBA and am having a problem understanding asynchronous
processes.
>
> I've a Form in Access that I want to start an out-of-process object that
> will run, basically, on its own until stopped by an outside event.
>
> My problem is that I don't understand how to start the object without
> getting the Form caught waiting for the object to stop processing.
>
> What I've done is create an ActiveX EXE component that houses two class
> objects, one that does the work (called the FNCreator) and a wrapper class
> (called the Creator).
>
> In my Access form I create an instance of the Creator class and tell it to
> create an instance of the FNCreator. When the Creator does this, it passes
a
> reference to itself, with events, to the FNCreator.
>
> To start the FNCreator, the Access form calls Creator.Start. Creator.Start
> then raises an event StartIt which is handled in FNCreator.
>
> I thought that Creator.Start would fire the event and go to the next
> instruction without jumping to FNCreator's StartIt() handler, but that is
not
> what happens. Instead Creator.Start gets caught waiting for the sub called
by
> the event to end and therefore doesn't return control to the Access form.
How
> would I implement this correctly?
>
> I'd love to hear if anyone has a helpful suggestion or can point me in the
> right direction for assisatance. Thanks!
>
> My simplified code looks like this:
>
> Access Form:
>
> Private Sub Toggle0_Click()
>
>     If Toggle0.Value = True Then
>         ...
>             Set myCreator = New Creator
>         ...
>             myCreator.create "FN"
>         ...
>         myCreator.start "FN"
>     Else
>         myCreator.ShutDown "FN"
>     End If
>
> End Sub
>
>
> Creator Class:
>
> Private myFNCreator As FNCreator
>
> Event FNStartIt()
> Event FNStopIt()
>
> Public Function Create(arg As String)
>
>     Select Case arg
>         Case "FN"
>             If Not myFNCreator Is Nothing Then
>                 ...
>             Else
>                 Set myFNCreator = New FNCreator
>                 Set myFNCreator.Parent = Me
>                 ...
>             End If
>         Case Else
>             ...
>     End Select
> End Function
>
> Public Function Start(arg As String)
>
>     Select Case arg
>         Case "FN"
>             If Not myFNCreator Is Nothing Then
>                 If myFNCreator.Active = False Then RaiseEvent FNStartIt
>             Else
>                 ...
>             End If
>         Case Else
>             ...
>         End Select
> End Function
>
> Public Function ShutDown(arg As String)
>
>     Select Case arg
>         Case "FN"
>             If Not myFNCreator Is Nothing Then
>                ...
>                RaiseEvent FNStopIt
>             Else
>                 ...
>             End If
>         Case Else
>             ...
>     End Select
> End Function
>
>
> FNCreator Class:
>
> Private booIsActive As Boolean
> Private WithEvents myParent As Creator
>
> Private Sub Class_Initialize()
>
>     booIsActive = False
>
> End Sub
>
> Private Sub Class_Terminate()
>
>     If Not myRecordset Is Nothing Then Set myRecordset = Nothing
>
> End Sub
>
> Friend Property Get Active() As Boolean
>
>     Active = booIsActive
>
> End Property
>
> Friend Property Set Parent(arg As Creator)
>
>     Set myParent = arg
>
> End Property
>
> Public Sub myParent_FNStartIt()
>
>     If booIsActive = True Then Exit Sub
>     booIsActive = True
>     ...
>
>     Do While booIsActive = True
>        ...
>     Loop
>     ...
> End Sub
>
> Public Sub myParent_FNStopIt()
>
>     booIsActive = False
>
> End Sub
>
>
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