wxMessageBox off the main thread lost result code.

[wxWidgets.git] / docs / doxygen / overviews / changes_since28.h

/////////////////////////////////////////////////////////////////////////////
// Name:        changes_since28.h
// Purpose:     topic overview
// Author:      Vadim Zeitlin
// Created:     2008-05-08
// Licence:     wxWindows licence
/////////////////////////////////////////////////////////////////////////////

/**

@page overview_changes_since28 Changes Since wxWidgets 2.8

This topic describes backwards-incompatible changes in wxWidgets 3.0 compared
to the last stable release.

The incompatible changes can be grouped into the following categories:

@li @ref overview_changes_unicode
@li @ref overview_changes_other


<hr>

@section overview_changes_unicode Unicode-related Changes

If you used Unicode build of wxWidgets 2.8 or previous version, please read
@ref overview_unicode for the details about how the API changed in 3.0 as a lot
of the information which was correct before doesn't apply any longer.

For example, the notorious (due to the confusion they created) macros @c wxT()
and @c _T() are not needed at all any longer. Basically, you can remove them
from any code which used them. On the other hand, there is no particular harm
in leaving them neither as the code will still compile and work correctly --
you only need to remove them if you think that your code looks tidier without
them. You also don't need to use @c wxChar any longer but can directly use the
standard @c wchar_t type even if, again, @c wxChar continues to work.

The most serious backwards-incompatible change is related to the change of
return type of wxString::c_str() method: it returns a special proxy object
instead of a simple @c char* or @c wchar_t* now. Because of this, you cannot
pass its result to any standard vararg functions such as @c printf() any more
as described in @ref overview_unicode_compilation_errors. All wxWidgets
functions, such as wxPrintf(), wxLogMessage() &c still work with it, but
passing it to @c printf() will now result in a crash. It is strongly advised to
recompile your code with a compiler warning about passing non-POD objects to
vararg functions, such as g++.

The change of the type of wxString::c_str() can also result in compilation
errors when passing its result to a function overloaded to take both narrow and
wide strings and in this case you must select the version which you really want
to use, e.g.:
@code
    void OpenLogFile(const char *filename);
    void OpenLogFile(const wchar_t *filename);

    wxString s;
    OpenLogFile(s);             // ERROR: ambiguity
    OpenLogFile(s.c_str());     // ERROR: ambiguity
    OpenLogFile(s.wx_str());    // OK: function called depends on the build
    OpenLogFile(s.mb_str());    // OK: always calls narrow string overload
    OpenLogFile(s.wc_str());    // OK: always calls wide string overload
@endcode
A common example of such problem arises with @c std::fstream class constructor
in Microsoft Visual C++ standard library implementation. In addition to a
constructor from @c const @c char * which this class must have, it also
provides a constructor taking a wide character file name. Because of this, code
like the following
@code
    #include <fstream>

    void MyFunc(const wxString& filename)
    {
        std::ifstream ifs(filename.c_str());
        ...
    }
@endcode
does not compile when using Microsoft Visual C++ and needs to be changed to use
mb_str() (which will not work for file names containing Unicode characters,
consider using wxWidgets classes and functions to work with such file names as
they are not supported by standard C++ library).

The other class of incompatible changes is due to modifying some virtual
methods to use @c wxString parameters instead of @c const @c wxChar* ones to
make them accept both narrow and wide strings. This is not a problem if you
simply call these functions but you need to change the signature of the derived
class versions if you override them as otherwise they wouldn't be called any
more. Again, the best way to ensure that this problem doesn't arise is to
rebuild your code using a compiler which warns about function signature
mismatch (you can use @c -Woverloaded-virtual g++ option).

Finally, a few structure fields, notable @c wxCmdLineEntryDesc::shortName,
@c longName and @c description fields have been changed to be of type @c const
@c char* instead of @c const @c wxChar* so you will need to remove @c wxT() or
@c _T() if you used it with their initializers.

@section overview_changes_other Miscellaneous Other Changes

- Default location of wxFileConfig files has changed under Windows, you will
  need to update your code if you access these files directly.

- wxWindow::IsEnabled() now returns false if a window parent (and not
  necessarily the window itself) is disabled, new function IsThisEnabled()
  with the same behaviour as old IsEnabled() was added.

- Generating wxNavigationKeyEvent events doesn't work any more under wxGTK (and
  other platforms in the future), use wxWindow::Navigate() or NavigateIn()
  instead.

- Sizers distribute only the extra space between the stretchable items
  according to their proportions and not all available space. We believe the
  new behaviour corresponds better to user expectations but if you did rely
  on the old behaviour you will have to update your code to set the minimal
  sizes of the sizer items to be in the same proportion as the items
  proportions to return to the old behaviour.

- wxWindow::Freeze/Thaw() are not virtual any more, if you overrode them in
  your code you need to override DoFreeze/Thaw() instead now.

- wxCalendarCtrl has native implementation in wxGTK, but it has less features
  than the generic one. The native implementation is used by default, but you
  can still use wxGenericCalendarCtrl instead of wxCalendarCtrl in your code if
  you need the extra features.

- wxDocument::FileHistoryLoad() and wxFileHistory::Load() now take const
  reference to wxConfigBase argument and not just a reference, please update
  your code if you overrode these functions and change the functions in the
  derived classes to use const reference as well.

- Calling wxConfig::Write() with an enum value will fail to compile because
  wxConfig now tries to convert all unknown types to wxString automatically
  using wxToString() function.

  The simplest solution is to cast the enum value to int, e.g.
  @code
    enum Colour { Red, Green, Blue };

    wxConfig conf;
    conf.Write("MyFavouriteColour", Red);       // ERROR: no match
    conf.Write("MyFavouriteColour", int(Red));  // OK
  @endcode

  Another possibility which exists now is to provide an overload of
  wxToString() (and wxFromString()) for your own type, e.g.

  @code
    wxString wxToString(Colour col)
    {
        return col == Red ? "R" : col == Green ? "G" : "B";
    }

    bool wxFromString(const wxString& s, Colour* col)
    {
        if ( s.length() != 1 )
            return false;

        switch ( s[0].GetValue() )
        {
            case 'R': *col = Red; return true;
            case 'G': *col = Green; return true;
            case 'B': *col = Blue; return true;
        }

        return false;
    }
  @endcode

  Of course, this will change the format of the wxConfig output which may be
  undesirable.

- wxTE_AUTO_SCROLL style is deprecated as it's always on by default anyhow in
  the ports which support it so you should simply remove any mentions of it
  from your code.

- If you use wxScrolled<T>::SetTargetWindow() you must override
  wxScrolled<T>::GetSizeAvailableForScrollTarget() method to compute the size
  available for the scroll target as function of the main window size, please
  see the documentation of this method for more details.

- Signature of wxDataViewCustomRenderer::StartDrag() virtual method changed.
  You will need to change it in your derived renderer class too if you override
  it.

- wxDataViewCustomRenderer::Activate() and
  wxDataViewCustomRenderer::LeftClick() were replaced with the new
  wxDataViewCustomRenderer::ActivateCell() method. You will need to change it
  in your derived renderer class accordingly.

*/