[AccessD] Multi-Instance Forms re-visited

Excellent... Thanks for that, so far I have not experienced any problems
but I don't think I'll wait for something to go wrong...

Thanks again

Mark

-----Original Message-----
From: accessd-bounces at databaseadvisors.com
[mailto:accessd-bounces at databaseadvisors.com] On Behalf Of Ken Ismert
Sent: 17 December 2004 17:32
To: 'Access Developers discussion and problem solving'
Subject: RE: [AccessD] Multi-Instance Forms re-visited



Jim, Mark, Francisco,

>I believe Hwnd is unique as well.
>
>Jim

See the Note in "hWnd Property",

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vb98/ht
ml/v
bprohwnd.asp

What Microsoft is saying in this topic, and the Access Help topic, is
that while the hWnd for a window will be unique, you can't count on it
to keep the same value over time.

So, if you key your form collection using hWnd, any function tries to
find the form instance in the collection based on the  current hWnd is
not guaranteed to work. The hWnd will still be unique, it just may not
be the same value you stored when you added the form to the collection.

In one of my object form managers, I use a class module-level variable
to guarantee a unique, stable ID:

Private lIDCounter As Long

Public Sub AddForm(rFrm As Access.Form)

    Dim sID As String

    lIDCounter = lIDCounter + 1
    sID = CStr(lIDCounter)
    colForms.Add rFrm, sID
    rFrm.SetInstanceID sID

End Sub

Of course, each form participating in this scheme now needs to have a
SetInstanceID method:

Private sInstanceID As String

Public Sub SetInstanceID(sID As String)
    sInstanceID = sID
End Sub

Now the form, when it is calling back to the managing object, can use
its sInstanceID to identify itself.

This is extra work, but do you want to be 99% sure your Form ID solution
will work, or 100%?

-Ken


-- 
AccessD mailing list
AccessD at databaseadvisors.com
http://databaseadvisors.com/mailman/listinfo/accessd
Website: http://www.databaseadvisors.com

---
Incoming mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.805 / Virus Database: 547 - Release Date: 03/12/2004
 

---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.805 / Virus Database: 547 - Release Date: 03/12/2004