-|
-
-wxWindows 2 for Windows FAQ
+ |
+
+wxWidgets for Windows FAQ
|
@@ -22,178 +23,335 @@ wxWindows 2 for Windows FAQ
See also top-level FAQ page.
+List of questions in this category
+
+
-Which Windows platforms are supported?
+
-wxWindows 2 can be used to develop and deliver applications on Windows 3.1, Win32s,
-Windows 95, Windows 98, and Windows NT. A Windows CE version is being looked into (see below).
+wxWidgets can be used to develop and deliver applications on Windows 95, Windows 98, Windows NT,
+Windows 2000, Windows XP, and Windows Vista. A Windows CE
+port is also available (see below).
-wxWindows 2 is designed to make use of WIN32 features and controls. However, unlike Microsoft,
-we have not forgotten users of 16-bit Windows. Most features
-work under Windows 3.1, including wxTreeCtrl and wxListCtrl using the generic implementation.
-However, don't expect very Windows-95-specific classes to work, such as wxTaskBarIcon. The wxRegConfig
-class doesn't work either because the Windows 3.1 registry is very simplistic. Check out the 16-bit
-makefiles to see what other files have been left out.
-
-16-bit compilation is supported under Visual C++ 1.5, and Borland BC++ 4 to 5.
+16-bit compilation is only supported for wxWidgets 2.4 and previous versions,
+using Visual C++ 1.5 and Borland BC++ 4 to 5.
-wxWindows 2 for Windows will also compile on Unix with gcc using TWIN32 from Willows,
-although TWIN32 is still in a preliminary state. The resulting executables are
-Unix binaries that work with the TWIN32 Windows API emulator.
+wxWidgets for Windows will also compile on Unix with gcc using Wine from WineHQ.
+The resulting executables are Unix binaries that work with the Wine Windows API emulator.
-You can also compile wxWindows 2 for Windows on Unix with Cygwin or Mingw32, resulting
+You can also compile wxWidgets for Windows on Unix with Cygwin or Mingw32, resulting
in executables that will run on Windows. So in theory you could write your applications
-using wxGTK or wxMotif, then check/debug your wxWindows for Windows
-programs with TWIN32, and finally produce an ix86 Windows executable using Cygwin/Mingw32,
+using wxGTK or wxMotif, then check/debug your wxWidgets for Windows
+programs with Wine, and finally produce an ix86 Windows executable using Cygwin/Mingw32,
without ever needing a copy of Microsoft Windows. See the Technical Note on the Web site detailing cross-compilation.
-
What about Windows CE?
+
+
+This port supports Pocket PC 2002/2003 and MS Smartphone 2002/2003, using
+Embedded Visual C++ 3 or 4. For further information, see the wxMSW section in
+the wxWidgets Reference Manual, and also the wxEmbedded page.
+
+
+
+From wxWidgets 2.5, the XP manifest is included in wx/msw/wx.rc and
+so your application will be themed automatically so long as you include wx.rc
+in your own .rc file.
+
+For versions of wxWidgets below 2.5, you need to provide the manifest
+explicitly, as follows.
+
+In the same directory as you have your executable (e.g. foo.exe) you
+put a file called foo.exe.manifest in which you have something like
+the following:
-This is under consideration, though we need to get wxWindows Unicode-aware first.
-There are other interesting issues, such as how to combine the menubar and toolbar APIs
-as Windows CE requires. But there's no doubt that it will be possible, albeit
-by mostly cutting down wxWindows 2 API functionality, and adding a few classes here
-and there. Since wxWindows for 2 produces small binaries (less than 300K for
-the statically-linked 'minimal' sample), shoehorning wxWindows 2 into a Windows CE device's limited
-storage should not be a problem.
+
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<assembly
+ xmlns="urn:schemas-microsoft-com:asm.v1"
+ manifestVersion="1.0">
+<assemblyIdentity
+ processorArchitecture="x86"
+ version="5.1.0.0"
+ type="win32"
+ name="foo.exe"/>
+ <description>Foo program</description>
+ <dependency>
+ <dependentAssembly>
+ <assemblyIdentity
+ type="win32"
+ name="Microsoft.Windows.Common-Controls"
+ version="6.0.0.0"
+ publicKeyToken="6595b64144ccf1df"
+ language="*"
+ processorArchitecture="x86"/>
+ </dependentAssembly>
+ </dependency>
+</assembly>
+
+
+If you want to add it to your application permanently,
+you can also include it in your .rc file using this
+line:
+
+
+ 1 24 "winxp.manifest"
+
+
+For an explanation of this syntax, please see
+this
+article.
+
-
What compilers are supported?
+
-Please see the wxWindows 2 for Windows install.txt file for up-to-date information, but
+Please see the wxWidgets for Windows install.txt file for up-to-date information, but
currently the following are known to work:
-- Visual C++ 1.5, 4.0, 5.0, 6.0
-
- Borland C++ 4.5, 5.0
-
- Borland C++Builder 1.0, 3.0
-
- Watcom C++ 10.6 (WIN32)
-
- Cygwin b20
+
- Visual C++ 1.5, 4.0, 5.0, 6.0, 7.0, 7.1
+
- Borland C++ 4.5, 5.0, 5.5
+
- Borland C++Builder 1.0, 3.0, X
+
- Watcom C++ 10.6 (Win32), OpenWatcom 1.0
+
- Cygwin (using configure)
- Mingw32
-
- MetroWerks CodeWarrior 4
+
- MetroWerks CodeWarrior (many versions)
+
- Digital Mars 8.34+
-There is a linking problem with Symantec C++ which I hope someone can help solve.
-
-
Which is the best compiler to use with wxWindows 2?
+
-It's partly a matter of taste, but I (JACS) prefer Visual C++ since the debugger is very
-good, it's very stable, the documentation is extensive, and it generates small executables.
-Since project files are plain text, it's easy for me to generate appropriate project files
-for wxWindows samples.
+It's partly a matter of taste, but some people prefer Visual C++ since the debugger is very
+good, it's very stable, the documentation is extensive, and it generates small executables.
+Since project files are plain text, it's easy for me to generate appropriate project files
+for wxWidgets samples.
-Borland C++ is fine - and very fast - but it's hard (impossible?) to use the debugger without using project files, and
-the debugger is nowhere near up to VC++'s quality. The IDE isn't great.
+Borland C++ is fine - and very fast - but it's hard (impossible?) to use the debugger without using project files, and
+the debugger is nowhere near up to VC++'s quality. The IDE isn't great.
-C++Builder's power isn't really used with wxWindows since it needs integration with its
-own class library (VCL). For wxWindows, I've only used it with makefiles, in which case
-it's almost identical to BC++ 5.0 (the same makefiles can be used).
+C++Builder's power isn't really used with wxWidgets since it needs integration with its
+own class library (VCL). For wxWidgets, I've only used it with makefiles, in which case
+it's almost identical to BC++ 5.0 (the same makefiles can be used).
-You can't beat Cygwin's price (free), and you can debug adequately using gdb. However, it's
+You can't beat Cygwin's price (free), and you can debug adequately using gdb. However, it's
quite slow to compile since it does not use precompiled headers.
CodeWarrior is cross-platform - you can debug and generate Windows executables from a Mac, but not
the other way around I think - but the IDE is, to my mind, a bit primitive.
-Watcom C++ is a little slow and the debugger is not really up to today's standards.
+Watcom C++ is a little slow and the debugger is not really up to today's standards.
+
+Among the free compilers the best choice seem to be Borland C++ command line
+tools and mingw32 (port of gcc to Win32). Both of them are supported by
+wxWidgets. However BC++ has trouble compiling large executables statically,
+so you need to dynamically link the wxWidgets libraries.
-
Is Unicode supported?
+
-Not yet, although there are other internationalisation features.
+Yes, Unicode is fully supported under Windows NT/2000 and there is limited
+support for it under Windows 9x using MSLU.
+
-However, the issues surrounding Unicode support have been looked into so we know
-what we need to do, and have some header files ready to use containing appropriate
-type definitions. Just about every file in wxWindows will need changes, due to the
-pervasive nature of characters and character arrays. Unicode support is needed
-for the port to Windows CE (see above), and will probably be added in time for version 2.1.
+
-Can you compile wxWindows 2 as a DLL?
+For Japanese under Win2000, it seems that wxWidgets has no problems working
+with double byte char sets (meaning DBCS, not Unicode). First you have to
+install Japanese support on your Win2K system and choose for ANSI translation
+HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Nls\CodePage=932
+(default is 1252 for Western). Then you can see all the Japanese letters in
+wxWidgets applications.
+
+
+
Yes (using the Visual C++ or Borland C++ makefile), but be aware that distributing DLLs is a thorny issue
-and you may be better off compiling statically-linked applications, unless you're
-delivering a suite of separate programs, or you're compiling a lot of wxWindows applications
+and you may be better off compiling statically-linked applications, unless you're
+delivering a suite of separate programs, or you're compiling a lot of wxWidgets applications
and have limited hard disk space.
-With a DLL approach, and with different versions and configurations of wxWindows
+With a DLL approach, and with different versions and configurations of wxWidgets
needing to be catered for, the end user may end up with a host of large DLLs in his or her Windows system directory,
negating the point of using DLLs. Of course, this is not a problem just associated with
-wxWindows!
+wxWidgets!
-
How can I reduce executable size?
+
-You can compile wxWindows as a DLL (see above, VC++/BC++ only at present). You should also
+You can compile wxWidgets as a DLL (see above, VC++/BC++ only at present). You should also
compile your programs for release using non-debugging and space-optimisation options, but
take with VC++ 5/6 space optimisation: it can sometimes cause problems.
-Statically-linked wxWindows 2 programs are smaller than wxWindows 1.xx programs, because of the way
-wxWindows 2 has been designed to reduce dependencies between classes, and other
-techniques. The linker will not include code from the library that is not (directly or
-indirectly) referenced
-by your application. So for example, the 'minimal' sample is less than 300KB using VC++ 6.
-
If you want to distribute really small executables, you can
-use Petite
+use Petite
by Ian Luck. This nifty utility compresses Windows executables by around 50%, so your 500KB executable
will shrink to a mere 250KB. With this sort of size, there is reduced incentive to
-use DLLs.
+use DLLs. Another good compression tool (probably better than Petite) is UPX.
+
+
+Please do not be surprised if MinGW produces a statically-linked minimal executable of 1 MB. Firstly, gcc
+produces larger executables than some compilers. Secondly, this figure will
+include most of the overhead of wxWidgets, so as your application becomes more
+complex, the overhead becomes proportionally less significant. And thirdly, trading executable compactness
+for the enormous increase in productivity you get with wxWidgets is almost always well worth it.
+
+If you have a really large executable compiled with MinGW (for example 20MB) then
+you need to configure wxWidgets to compile without debugging information: see
+docs/msw/install.txt for details. You may find that using configure instead
+of makefile.g95 is easier, particularly since you can maintain debug and
+release versions of the library simultaneously, in different directories.
+Also, run 'strip' after linking to remove all traces of debug info.
+
-
Is wxWindows compatible with MFC?
+
-There is a sample which demonstrates MFC and wxWindows code co-existing in the same
-application. However, don't expect to be able to enable wxWindows windows with OLE-2
+There is a sample which demonstrates MFC and wxWidgets code co-existing in the same
+application. However, don't expect to be able to enable wxWidgets windows with OLE-2
functionality using MFC.
-
Why do I sometimes get bizarre crash problems using VC++ 5/6?
+
+
+When you build the wxWidgets library, setup.h is copied
+from include/wx/msw/setup.h to e.g. lib/vc_msw/mswd/wx/setup.h (the path
+depends on the configuration you're building). So you need to add
+this include path if building using the static Debug library:
+
+lib/vc_lib/mswd
+
+or if building the static Release library, lib/vc_lib/msw.
+
+See also the wxWiki Contents
+for more information.
+
+
+
+
+If you get errors like
+
+
+no matching function for call to 'wxDC::DrawTextA(const char[5], int,
+int)'
+
+
+or similar ones for the other functions, i.e. the compiler error messages
+mention the function with the 'A' suffix while you didn't
+use it in your code, the explanation is that you had included
+<windows.h> header which redefines many symbols to have such
+suffix (or 'W' in the Unicode builds).
+
+
+The fix is to either not include <windows.h> at all or include
+"wx/msw/winundef.h" immediately after it.
+
+
+
+The most common cause of this problem is the memory debugging settings in
+wx/msw/setup.h. You have several choices:
+
+
+ - Either disable overloading the global operator new completely by
+ setting wxUSE_GLOBAL_MEMORY_OPERATORS and
+ wxUSE_DEBUG_NEW_ALWAYS to 0 in this file
+
- Or leave them on but do #undef new after including any
+ wxWidgets headers, like this the memory debugging will be still on
+ for wxWidgets sources but off for your own code
+
+
+Notice that IMHO the first solution is preferable for VC++ users who can use
+the VC++ CRT memory debugging features instead.
+
+
+
+Set up your interface from scratch using wxWidgets (especially wxDesigner
+or DialogBlocks --
+it'll save you a lot of time) and when you have a shell prepared, you can start
+'pouring in' code from the MFC app, with appropriate
+modifications. This is the approach I have used, and I found
+it very satisfactory. A two-step process then - reproduce the bare
+interface first, then wire it up afterwards. That way you deal
+with each area of complexity separately. Don't try to think MFC
+and wxWidgets simultaneously from the beginning - it is easier to
+reproduce the initial UI by looking at the behaviour of the MFC
+app, not its code.
+
+
Some crash problems can be due to inconsistent compiler
-options (and of course this isn't limited to wxWindows).
+options (and of course this isn't limited to wxWidgets).
If strange/weird/impossible things start to happen please
check (dumping IDE project file as makefile and doing text comparison
if necessary) that the project settings, especially the list of defined
symbols, struct packing, etc. are exactly the same for all items in
the project. After this, delete everything (including PCH) and recompile.
-VC++ 5's optimization code seems to be broken and can
+VC++ 5's optimization code seems to be broken and can
cause problems: this can be seen when deleting an object Dialog
Editor, in Release mode with optimizations on. If in doubt,
switch off optimisations, although this will result in much
larger executables. It seems possible that the library can be created with
strong optimization, so long as the application is not strongly
-optimized. For example, in wxWindows project, set to 'Minimum
-Size'. In Dialog Editor project, set to 'Customize: Favor Small
-Code' (and no others). This will then work.
+optimized. For example, in wxWidgets project, set to 'Minimum
+Size'. In Dialog Editor project, set to 'Customize: Favor Small
+Code' (and no others). This will then work.
-
How are the wxWindows makefiles edited under Windows?
+
-As of wxWindows 2.1, there is a new system written by Vadim Zeitlin, that
+wxWidgets 2.5.x and above uses Bakefile to generate makefiles, which
+is described in technical note 16 under docs/tech in your distribution.
+
+For 2.4.x, there is a system written by Vadim Zeitlin that
generates the makefiles from templates using tmake.
-Here are Vadim's notes:
+Here are Vadim's notes on tmake:
-To use these new makefiles, you don't need anything (but see below).
+To use these new makefiles, you don't need anything (but see below).
However, you should NOT modify them because these files will be
rewritten when I regenerate them using tmake the next time. So, if
you find a problem with any of these makefiles (say, makefile.b32)
-you'll need to modify the corresponding template (b32.t in this
+you'll need to modify the corresponding template (b32.t in this
example) and regenerate the makefile using tmake.
tmake can be found at
www.troll.no/freebies/tmake.html.
-It's a Perl5 program and so it needs Perl (doh). There is a binary for
-Windows (available from the same page), but I haven't used it, so
-I don't know if it works as flawlessly as "perl tmake" does (note
-for people knowing Perl: don't try to run tmake with -w, it won't
+It's a Perl5 program and so it needs Perl (doh). There is a binary for
+Windows (available from the same page), but I haven't used it, so
+I don't know if it works as flawlessly as "perl tmake" does (note
+for people knowing Perl: don't try to run tmake with -w, it won't
do you any good). Using it extremely simple: to regenerate makefile.b32
just go to distrib/msw/tmake and type
tmake -t b32 wxwin.pro -o ../../src/msw/makefile.b32
-The makefiles are untested - I don't have any of Borland, Watcom or
-Symantec and I don't have enough diskspace to recompile even with
+The makefiles are untested - I don't have any of Borland, Watcom or
+Symantec and I don't have enough diskspace to recompile even with
VC6 using makefiles. The new makefiles are as close as possible to the
old ones, but not closer: in fact, there has been many strange things
(should I say bugs?) in some of makefiles, some files were not compiled
@@ -205,35 +363,35 @@ The templates are described in tmake ref manual (1-2 pages of text)
and are quite simple. They do contain some Perl code, but my Perl is
primitive (very C like) so it should be possible for anybody to make
trivial modifications to it (I hope that only trivial modifications
-will be needed). I've tagged the ol makefiles as MAKEFILES_WITHOUT_TMAKE
+will be needed). I've tagged the ol makefiles as MAKEFILES_WITHOUT_TMAKE
in the cvs, so you can always retrieve them and compare the new ones,
this will make it easier to solve the problems you might have.
Another important file is filelist.txt: it contains the list of all
files to be compiled. Some of them are only compiled in 16/32 bit mode.
-Some other are only compiled with some compilers (others can't compile
+Some other are only compiled with some compilers (others can't compile
them) - all this info is contained in this file.
-So now adding a new file to wxWindows is as easy as modifying filelist.txt
+So now adding a new file to wxWidgets is as easy as modifying filelist.txt
(and Makefile.ams for Unix ports) and regenerating the makefiles - no
need to modify all files manually any more.
Finally, there is also a file vc6.t which I use myself: this one
-generates a project file for VC++ 6.0 (I didn't create vc5.t because
-I don't need it and can't test it, but it should be trivial to create
+generates a project file for VC++ 6.0 (I didn't create vc5.t because
+I don't need it and can't test it, but it should be trivial to create
one from vc6.t - probably the only things to change would be the
-version number in the very beginning and the /Z option - VC5 doesn't
+version number in the very beginning and the /Z option - VC5 doesn't
support edit-and=continue). This is not an officially supported way
-of building wxWindows (that is, nobody guarantees that it will work),
+of building wxWidgets (that is, nobody guarantees that it will work),
but it has been very useful to me and I hope it will be also for
-others. To generate wxWindows.dsp run
+others. To generate wxWidgets.dsp run
-
tmake -t vc6 wxwin.pro -o ../../wxWindows.dsp
+
tmake -t vc6 wxwin.pro -o ../../wxWidgets.dsp
Then just include this project in any workspace or open it from VC IDE
and it will create a new workspace for you.
-If all goes well, I'm planning to create a template file for Makefile.ams
+If all goes well, I'm planning to create a template file for Makefile.ams
under src/gtk and src/motif and also replace all makefiles in the samples
subdirectories with the project files from which all the others will be
generated. At least it will divide the number of files in samples
@@ -242,21 +400,21 @@ directory by 10 (and the number of files to be maintained too).
-
How do you use VC++'s memory leak checking instead of that in wxWindows?
+
Vadim Zeitlin:
-On the VC++ level, it's just the matter of calling _CrtSetDbgFlag() in the very
-beginning of the program. In wxWindows, this is done automatically when
+On the VC++ level, it's just the matter of calling _CrtSetDbgFlag() in the very
+beginning of the program. In wxWidgets, this is done automatically when
compiling with VC++ in debug mode unless wxUSE_GLOBAL_MEMORY_OPERATORS or
__NO_VC_CRTDBG__ are defined - this check is done in wx/msw/msvcrt.h which
is included from app.cpp which then calls wxCrtSetDbgFlag() without any
-#ifdefs.
+ifdefs.
This works quite well: at the end of the program, all leaked blocks with their
malloc count are shown. This number (malloc count) can be used to determine
-where exactly the object was allocated: for this it's enough to set the variable
+where exactly the object was allocated: for this it's enough to set the variable
_crtBreakAlloc (look in VC98\crt\srs\dbgheap.c line 326) to this number and
a breakpoint will be triggered when the block with this number is allocated.
@@ -267,6 +425,149 @@ Regards,
VZ
+
+
+
+
+This can happen if you have a child window intercepting EVT_CHAR events and swallowing
+all keyboard input. You should ensure that event.Skip() is called for all input that
+isn'used by the event handler.
+
+It can also happen if you append the submenu to the parent
+menu {\it before} you have added your menu items. Do the append {\it after} adding
+your items, or accelerators may not be registered properly.
+
+
+
+Currently this is not possible because the wxConfig family of classes is
+supposed to deal with per-user application configuration data, and HKLM is
+only supposed to be writeable by a user with Administrator privileges. In theory,
+only installers should write to HKLM. This is still a point debated by the
+wxWidgets developers. There are at least two ways to work around it if you really
+need to write to HKLM.
+
+First, you can use wxRegKey directly, for example:
+
+
+ wxRegKey regKey;
+
+ wxString idName(wxT("HKEY_LOCAL_MACHINE\\SOFTWARE\\My Company\\My Product\\Stuff\\"));
+ idName += packid;
+
+ regKey.SetName(idName);
+
+ {
+ wxLogNull dummy;
+ if (!regKey.Create())
+ {
+ idName = wxT("HKEY_CURRENT_USER\\SOFTWARE\\My Company\\My Product\\Stuff\\");
+ idName += packid;
+ regKey.SetName(idName);
+ if (!regKey.Create())
+ return FALSE;
+ }
+ }
+
+ if (!regKey.SetValue(wxT("THING"), (long) thing)) err += 1;
+
+ regKey.Close();
+
+
+
+Or, you can employ this trick suggested by Istvan Kovacs:
+
+
+class myGlobalConfig : public wxConfig
+{
+ myGlobalConfig() :
+ wxConfig ("myApp", "myCompany", "", "", wxCONFIG_USE_GLOBAL_FILE)
+{};
+ bool Write(const wxString& key, const wxString& value);
+}
+
+bool myGlobalConfig::Write (const wxString& key, const wxString& value)
+{
+ wxString path = wxString ("SOFTWARE\\myCompany\\myApp\\") + wxPathOnly(key);
+ wxString new_path = path.Replace ("/", "\\", true);
+ wxString new_key = wxFileNameFromPath (key);
+ LocalKey().SetName (wxRegKey::HKLM, path);
+ return wxConfig::Write (new_key, value);
+}
+
+
+
+
+This is being worked on. Please see this page
+for the current status.
+
+
+
+
+
+
+If you have downloaded the wxWidgets sources from the cvs using a Unix cvs
+client or downloaded a daily snapshot in .tar.gz format, it is likely
+that the project files have Unix line endings (LF) instead of the DOS ones (CR
+LF). However all versions of Visual C++ up to and including 7.1 can only open
+the files with the DOS line endings, so you must transform the files to this
+format using any of the thousands ways to do it.
+
+Of course, another possibility is to always use only the Windows cvs client
+and to avoid this problem completely.
+
+
+
+
+If you get errors like this
+
+
+MSVCRTD.lib(MSVCRTD.dll) : error LNK2005: _xxxxxx already defined in LIBCD.lib(yyyyy.obj)
+
+
+when linking your project, this means that you used different versions of CRT
+(C Run-Time) library for wxWindows (or possibly another library) and the main
+project. Visual C++ provides static or dynamic and multithread safe or not
+versions of CRT for each of debug and release builds, for a total of 8
+libraries. You can choose among them by going to the "Code generation"
+page/subitem of the "C++" tab/item in the project proprieties dialog in VC6/7.
+
+To avoid problems, you must use the same one for all
+components of your project. wxWindows uses multithread safe DLL version of the
+CRT which is a good choice but may be problematic when distributing your
+applications if you don't include the CRT DLL in your installation -- in this
+case you may decide to switch to using a static CRT version. If you build with
+wxUSE_THREADS == 0 you may also use the non MT-safe version as it is
+slightly smaller and faster.
+
+But the most important thing is to use the same CRT setting for
+all components of your project.
+
+
+
+If you get errors when including Microsoft DirectShow or DirectDraw headers,
+the following message from Peter Whaite could help:
+
+> This causes compilation errors within DirectShow:
+>
+> wxutil.h(125) : error C2065: 'EXECUTE_ASSERT' : undeclared identifier
+> amfilter.h(1099) : error C2065: 'ASSERT' : undeclared identifier
+
+The reason for this is that __WXDEBUG__ is also used by the DXSDK (9.0
+in my case) to '#pragma once' the contents of
+DXSDK/Samples/C++/DirectShow/BaseClasses/wxdebug.h. So if __WXDEBUG__
+is defined, then wxdebug.h doesn't get included, and the assert macros
+don't get defined. You have to #undef __WXDEBUG__ before including the
+directshow baseclass's <streams.h>.
+
+
+
+
+
+To handle a Windows message you need to override a virtual
+MSWWindowProc() method in a wxWindow-derived class. You should then
+test if nMsg parameter is the message you need to process and perform
+the necessary action if it is or call the base class method otherwise.
+