Create the equivalent of Form.Unload?

[Michael Burns]

I am in the process of doing an exploratory porting an
application from Visual Basic 6.0 over to PowerBASIC 6.0.
I am also new to PowerBASIC, havng started using it only
about a month ago, but have been using Visual Basic since
it first came out many many moons ago. Anyway, one of the
Visual Basic aspects I have not been able to emulate after
several days of trying is the Form.Unload and Form.UnloadQuery
routines. For those of you who don't use VB, these routines
are where you place any code you want executed when a form
(dialog) is unloaded. If the form in question is the main
application form, that code will be executed no matter how
the program is terminated, be it by a controlled END statement
in the code or the user clicking the upper right X of the
application's window, hitting Alt-F4, or most importantly,
the operating system itself closing the application as it
might if the user tells Windows to restart. The main use,
and what I am using them for, is to place the cleanup code
that I want executed when the main application, which is a
TSR so its form is actually never visible, is terminated.

Anyway, I assume one can achieve this in PB using a callback on
the main dialog although on a hidden form (dialog) this
may not be the way to do it, but so far I don't seem to be
able to rig a callback up to do this correctly even with a
dialog that is visible.

Anyone out there know how to achieve the equivalent of a Visual
Basic UnLoad subroutine?


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[Jim Huguley]

Michael..

The CallBack Message %WM_DESTROY is the equivelent to Unload.
%WM_CLOSE is the equivelent to Query_Unload.

I would suggest that you put a MsgBox in each so that you can
see them being triggered to better understand.




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Jim..
[email protected]

[Michael Burns]

Thanks!

It's amazing how useful a nudge in the right direction can be!


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[Edwin Knoppert]

If you use a debugger you'll see WM_SYSCOMMAND before %WM_CLOSE.
I suggest you use this for queryunload

In VB6 the Form_Unload would be WM_CLOSE where the Terminate event is the WM_DESTROY.


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[Jim Huguley]

Edwin...

As far as I know the %WM_SYSCOMMAND/%SC_CLOSE is only sent from
a System Menu Item such as clicking the X or by way of code such
as when you would use something like

SendMessage hWnd,%WM_SYSCOMMAND,%SC_CLOSE,BYVAL %NULL

in response to invoking an F4, Exit, Quit,etc.. Menu Sub Item. You
may even send this message from a Button on your form to close
your program for some reason. Although this is not 100% sure
because using DDT and

DIALOG END CBHNDL

the %WM_SYSCOMMAND
is NOT processed, it goes directly to %WM_CLOSE. This is why my
conclusions are as stated above in my original reply. In coding
practice, I use the following code in order to accomodate the
%WM_SYSCOMMAND/%SC_CLOSE when my users exit using the X.

    CASE %WM_SYSCOMMAND
        IF wParam = %SC_CLOSE THEN
            SendMessage hWnd, %WM_CLOSE, 0, 0
    ...etc....

If I treated %WM_SYSCOMMAND as Query_Unload then the code may or
may not be processed depending on several of the above items.
If your understanding is different than this, I would appreciate
your perspective and correction.


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Jim..
[email protected]

[Edwin Knoppert]

We both have a point but, it was compared to VB.

Queryunload does tell you how it happend, WM_CLOSE not.
So, i compared it equally as in VB.

It's probably true that SYSCOMMAND will not be executed when no sysmenu is available.
This is something it simply cannot be compared with VB.

If the window is in the wm_destroy message, it cannot prevent unloading while VB still can!

Just my opinion..


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[K Peel]

I think the system menu close button on standard
dialogs has an ID of %IDCANCEL (which is 2), in my
applications I use the %WM_COMMAND => %IDCANCEL
message to execute DestroyWindow\EndDialog after
prompting the user to exit, then all cleanup code etc.
is placed in the dialog's %WM_DESTROY message.

I don't bother with %WM_CLOSE at all, personally.

Regards,

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Kev G Peel
KGP Software
Bridgwater, UK.
mailto:[email protected][email protected]</A>

[Edwin Knoppert]

IDOK and IDCancel do come from the message pump.
Prob. 'IsDialogMessage'
Ideal to use as Default or Cancel button.


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[Steve Hutchesson]

Michael,

Jim has pointed you in the right direction, as I understand you are looking
for the correct place to test if a window is being closed, an emulation of
the VB idea so WM_CLOSE is the right place in a CreateWindowEx message
handling proc to do your testing.

Kevin has raised an interesting question, a dialog box does not normally
use a WM_CLOSE message but you can access the EndDialog() location and do
much the same thing just before it is called.

Porting a VB application will need some architectural changes to get it to
work properly as a API based win32 application is structurally different
but you can get the functionality without any real problems once you get
the swing of it.

You have a few other options as well with windows, you can easily show and
hide them using ShowWindow(hWnd,%SW_SHOW / %SW_HIDE). You can simply destroy
the window and recreate it again when you need it. It just depends on what
your application needs.

Regards & good luck with the port.

[email protected]

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