AW: WM_GETDLGCODE infinite message loop

Graham -- Cunningham@tgd.swissptt.ch
Monday, April 22, 1996

[Mini-digest: 2 responses]

This was on the list a while ago heres the answer
-- snatched from usenet.
> Unpublished article from Microsoft:
> ---------------------------------------------------------------------
>=20
> Subject:
>   Date:
>         Fri, 1 Mar 96 09:11:28 TZ
>   From:
>         Sergey Zarembsky (Stream) 
>     To:
>         mplante@versus.com
>=20
> .TITLE:                Child CPropertySheet Hangs If Focus Is Switched
> .VERSION(S):         4.00
> .OPERATING SYSTEM(S):WINDOWS NT
>=20
> -----------------------------------------------------------------------=

> The information in this article applies to:
>=20
>  - The Microsoft Foundation Classes (MFC), included with:
>    Microsoft Visual C++, 32-bit Edition, version 4.0
> -----------------------------------------------------------------------=

>=20
> SYMPTOMS
> =3D=3D=3D=3D=3D=3D=3D=3D
>=20
> If a CPropertySheet is a child of a CDialog or another CPropertySheet,
> and focus is placed in a control inside the child CPropertySheet, when
> you switch focus to another window, the program will hang. The program
> will also hang if focus is on a control and you close the sheet. The
> child CPropertySheet continually gets a WM_GETDLGCODE.
>=20
> CAUSE
> =3D=3D=3D=3D=3D
>=20
> By default, CPropertyPages will have a style of WS_EX_CONTROLPARENT.
> CPropertySheets will not have this style.  This style allows a user to
> tab from a control inside the page to one in the sheet.
>=20
> When focus is switched from the parent sheet, code which handles
> default push buttons loops through all the controls in the pages and
> the sheet.  Cycling through controls is done using GetNextDlgTabItem().=

> The loop cycles through controls in the page in the child
> CPropertySheet and finds its way to controls in the parent page or
> parent dialog.  At this point, GetNextTabItem() is not able to find
> controls inside the child CPropertySheet since it doesn't have a style
> of WS_EX_CONTROLPARENT.  The loop never ends because it never finds the=

> original control that had focus.
>=20
> RESOLUTION
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>=20
> Override OnInitDialog() for the child CPropertySheet and add the
> WS_EX_CONTROLPARENT style.
>=20
> STATUS
> =3D=3D=3D=3D=3D=3D
>=20
> Microsoft has confirmed this to be a bug in the Microsoft products
> listed at the beginning of this article. We are researching this bug
> and will post new information here in the Microsoft Knowledge Base as
> it becomes available.
>=20
> MORE INFORMATION
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>=20
> REFERENCES
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>=20
> Sample Code
> -----------
>=20
> // CMySheet is derived from CPropertySheet
> BOOL CMySheet::OnInitDialog()
> {
>   ModifyStyleEx (0, WS_EX_CONTROLPARENT);
>=20
>   return CPropertySheet::OnInitDialog();
> }
>=20
> /* Compile options needed: default
>=20
> This article might help you!



Graham Cunningham=20
email         : Cunningham@tgd.swissptt.ch
phone       : 00 41 31 338 0633

-----From: Ghislain Lachapelle 

>OS = Windows NT 3.51
>VC++ 4.1
>Dell Dimension XPS P90
>32 MB Ram
>

I have NT 3.51, VC++ 4.1, Alr Evolution X P90 and 32 MB RAM.

What a coincidence? I built a prototype yesterday afternoon which seems
exactly what you did and got very similar results. 

>I have a modeless Prop sheet.  In one page of the sheet, I create another
>modeless Prop sheet.  When I first select the page, which then loads the   
>nested
>Prop sheet all is well.  If I then select a second page from the nested   
>property sheet,
>then select the first page on the parent prop sheet, I enter an infinite   
>loop.  It appears
>that the child prop sheet is sending a WM_GETDLGCODE message to itself   
>repeatedly.
>

I break in the code during the infinite loop and had your WM_GETDLGCODE
message. I also found another message which is WM_NOTIFY with a
PSN_SETACTIVE parameter. I tried to add the style NO PARENT NOTIFY to the
property page but the MFC CPropertyPage code asserts on any extended style.

I do not have any workaround for now and think a derivation of OnNotity
function is a good start to search. 

N.B.: I put breakpoint in all OnSetActive functions (in all property page)
and did not encountered the infinite loop. Perhaps this will help you.




////////////////////////////////////////////////////
Ghislain Lachapelle(Ghislain.Lachapelle@matrox.com)

Ghislain Lachapelle
Matrox Electronic Systems Ltd.
Imaging Group
1055 St-Regis Blvd.
Dorval, Quebec, Canada
H9P 2T4


(514) 685-7230, ext. 2495
////////////////////////////////////////////////////

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    .      .       "-:______________  |____l_|]'''''''''''       .     .
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         .                 -)-----====   `.   `.              LS
                     .            -)-------+====+       .            .
             .                               .

---

David W. Gillett -- DGILLETT@expertedge.com
Wednesday, April 24, 1996

> > Unpublished article from Microsoft:
...
> > Override OnInitDialog() for the child CPropertySheet and add the
> > WS_EX_CONTROLPARENT style.


  Note that you must derive your own class from CPropertySheet and 
add this there.  If you try to pass this as a style to 
CPropertySheet::Create(), you will find another way into the 
WM_GETDLGCODE infinite loop....

Dave

---

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