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Porting to Qt 3.xThis document describes porting applications from Qt 2.x to Qt 3.x. The Qt 3.x series is not binary compatible with the 2.x series. This means programs compiled for Qt 2.x must be recompiled to work with Qt 3.x. Qt 3.x is also not completely source compatible with 2.x, however all points of incompatibility cause compiler errors or run-time messages (rather than mysterious results). Qt 3.x includes many additional features and discards obsolete functionality. Porting from Qt 2.x to Qt 3.x is straightforward, and once completed makes the considerable additional power and flexibility of Qt 3.x available for use in your applications. To port code from Qt 2.x to Qt 3.x:
Table of contents:
On Windows, originally in Qt 2.x, the default configuration of the Qt
library is static. If you just use the default configuration you
don't need to set certain preprocessor defines. In Qt 3.0, the
default configuration of the Qt library is to build it as a shared
library, therefore the preprocessor define QT_DLL is needed.
If you use tmake with Qt 2.x, and now use qmake with Qt 3.x, then the
cause of the problem is with the project file. In the project file,
there is usually line that looks like:
CONFIG = ...
this should be changed to
CONFIG += ...
so that qmake can look at the configuration that Qt was built with and
set any relevant preprocessor defines in the makefile.
Qt 3.x remove some unnecessary nested #include directives from
header files. This speeds up compilation when you don't need those
nested header files. But in some cases you will find you need to add
an extra #include to your files.
For example, if you get a message about QStringList or its functions
not being defined, then add #include <qstringlist.h> at
the top of the file giving the error.
Header files that you might need to add #include directives for include:
Qt 3.x is namespace clean. A few global identifiers that had been
left in Qt 2.x have been discarded.
Enumeration Qt::CursorShape and its values are now part of the
special Qt class defined in qnamespace.h. If you get compilation
errors about these being missing (unlikely, since most of your code will
be in classes that inherit from the Qt namespace class), then apply
the following changes:
The names of some debugging macro variables have been changed. We have
tried not to break source compatibility as much as possible. If you observe
error messages on the UNIX console or the Windows debugging stream that were
previously disabled, please check these macro variables:
The name of some debugging macro functions has been changed as well
but source compatibility should not be affected if the macro variable
QT_CLEAN_NAMESPACE is not defined:
For the record, undocumented macro variables that are not part of the API
have been changed:
All these functions have been removed in Qt 3.x:
Also, to avoid conflicts with <iostream>, the following three
global functions have been renamed:
The following functions have been obsoleted in Qt 3.0. The
documentation of each of these functions should explain how to
replace them in Qt 3.0.
Warning: It is best to consult http://doc.trolltech.com/3.0/
rather than the documentation supplied with Qt to obtain the latest
information regarding obsolete functions and how to replace them in
new code.
Additionally, these preprocessor directives have been removed:
See the changes-3.0.0 document for an explanation of why this had to be done.
You might have been relying on the non-portable and unpredictable behavior
resulting from these directives. We strongly recommend that you either make
use of the safe qstr* variants directly or ensure that no 0 pointer is
passed to the standard C functions in your code base.
The classes QArray, QCollection, QList, QListIterator, QQueue, QStack
and QVector have been renamed. To ease porting, the old names and the
old header-file names are still supported.
In Qt 2.x, the function QButtonGroup::selected() returns the selected
radio button (QRadioButton). In Qt 3.0, it returns the selected toggle button (QButton::toggleButton), a more general concept.
This might affect programs that use QButtonGroups that contain a
mixture of radio buttons and non-radio (e.g. QCheckBox) toggle buttons.
Two QDate member functions that were virtual in Qt 2.0 are not virtual
in Qt 3.0. This is only relevant if you subclassed QDate and
reimplemented these functions:
In addition to no longer being virtual, QDate::monthName() and
QDate::dayName() have been renamed QDate::shortMonthName() and
QDate::shortDayName() and have been made static (as they should had
been in the first place). The old names are still provided for source
compatibility.
If the mode was not set explicitly, and the user entered a
non-existent file, the dialog would accept this. In Qt 3.x, you must
set the mode, e.g. setMode(QFileDialog::AnyFile), to get the same
behavior.
The internals of QFont have changed significantly between Qt 2.2 and
Qt 3.0, to give better Unicode support and to make developing
internationalized applications easier. The original API has been
preserved with minimal changes. The CharSet enum and its related
functions have disappeared. This is because Qt now handles all charset
related issues internally, and removes this burden from the developer.
If you used the CharSet enum or its related functions, e.g
QFont::charSet() or QFont::setCharSet(), just remove them from your
code. There are a few functions that took a QFont::CharSet as a
parameter; in these cases simply remove the charset from the
parameter list.
The two static getText(...) methods in QInputDialog have been merged.
The echo parameter is the third parameter and defaults to
QLineEdit::Normal.
If you used calls to QInputDialog::getText(...) that provided more
than the first two required parameters you will must add a value
for the echo parameter.
The definitions of QGLayoutIterator, QLayout, QLayoutItem, QLayoutIterator, QSpacerItem and QWidgetItem have been moved from <qabstractlayout.h> to <qlayout.h>. The header <qabstractlayout.h> now includes <qlayout.h> for compatibility. It
might be removed in a future version.
The paintBranches() function in Qt 2.x had a GUIStyle parameter; this
has been dropped for Qt 3.x since GUI style is handled by the new
style engine (See QStyle.)
In Qt 2.x, the function QMoveEvent::pos() returned the position of the
widget in its parent widget, including the window frame. In Qt 3.0,
it returns the new position of the widget, excluding window frame for
top level widgets.
The QMultiLineEdit was a simple editor widget in previous Qt versions.
Since Qt 3.0 includes a new richtext engine, which also supports
editing, QMultiLineEdit is obsolete. For the sake of compatibility
QMultiLineEdit is still provided. It is now a subclass of QTextEdit
which wraps the old QMultiLineEdit so that it is mostly source
compatible to keep old applications working.
For new applications and when maintaining existing applications we
recommend that you use QTextEdit instead of QMultiLineEdit wherever
possible.
Although most of the old QMultiLineEdit API is still available, there
is one important difference. The old QMultiLineEdit operated in terms
of lines, whereas QTextEdit operates in terms of paragraphs. This is
because lines change all the time during wordwrap, whereas paragraphs
remain paragraphs. The consequence of this change is that functions
which previously operated on lines, e.g. numLines(), textLine(), etc.,
now work on paragraphs.
Also the function getString() has been removed since it
published the internal data structure.
In most cases, applications that used QMultiLineEdit will continue to
work without problems. Applications that worked in terms of lines may
require some porting.
The source code for the old 2.x version of QMultiLineEdit can be found
in $QTDIR/src/attic/qtmultilineedit.h/cpp. Note that the class has
been renamed to QtMultiLineEdit to avoid name clashes. If you really
need to keep compatibility with the old QMultiLineEdit, simply include
this class in your project and rename QMultiLineEdit to
QtMultiLineEdit throughout.
QPrinter has undergone some changes, to make it more flexible and
to ensure it has the same runtime behaviour on both Unix and Windows. In 2.x,
QPrinter behaved differently on Windows and Unix, when using view
transformations on the QPainter. This has changed now, and QPrinter
behaves consistently across all platforms. A compatibilty mode has been
added that forces the old behaviour, to ease porting from Qt 2.x
to Qt 3.x. This compatibilty mode can be enabled by passing the
QPrinter::Compatible flag to the QPrinter constructor.
On X11, QPrinter used to generate encapsulated postscript when
fullPage() was TRUE and only one page was printed. This does not
happen by default anymore, providing a more consistent printing output.
The QRegExp class has been rewritten to support many of the features of Perl
regular expressions. Both the regular expression syntax and the QRegExp
interface have been modified.
Be also aware that <qregexp.h> is no longer included
automatically when you include <qstringlist.h>. See
above for details.
There are five new special characters: (, ), {,
| and } (parentheses, braces and pipe). When porting old
regular expressions, you must add \ (backslash) in front of any
of these (actually, \\ in C++ strings), unless it is already
there.
Example: Old code like
Wildcard patterns need no conversion. Here are two examples:
This function has been replaced by QRegExp::setPattern() in Qt 2.2.
Old code such as
The following function is now obsolete, as it has an unwieldy
parameter list and was poorly named:
This function was removed, after a brief appearance in Qt 2.2. Its
name clashed with QString::find(). Use QRegExp::search() or QString::find() instead.
QString::findRev()'s and QString::contains()'s semantics have changed
between 2.0 and 3.0 to be more consistent with the other overloads.
For example,
This change affect very few existing programs.
With Qt 1.0 and 2.0, a QString is converted implicitly into a QRegExp
as the first argument to QString::replace():
The QSemiModal class is now obsolete. You should call show() on a
modal dialog instead.
The QSortedList class is now obsolete. Consider using a QDict, a QMap
or a plain QPtrList instead.
The QTableView class has been obsoleted and is no longer a part of the
Qt API. Either use the powerful QTable class or the simplistic
QGridView in any new code you create. If you really need the old table
view for compatibility you can find it in $QTDIR/src/attic/qttableview.{cpp,h}. Note that the class has been
renamed from QTableView to QtTableView to avoid name clashes. To use
it, simply include it in your project and rename QTableView to
QtTableView throughout.
The QToolButton class used to distinguish between "on" and "off"
icons. In 3.0, this mechanism was moved into the QIconSet class
(see QIconSet::State).
The old QToolButton::onIconSet and QToolButton::offIconSet
properties are still provided so that old source will compile, but
their semantics have changed: they are now synonyms for QToolButton::iconSet. If you used that distinction in Qt 2.x, you will
need to adjust your code to use the QIconSet On/Off mechanism.
Likewise, the on parameter of these two functions is now ignored:
These functions are only provided for ease of porting. New code
should use the following instead:
Finally, this function is no longer virtual:
If you have a class that inherits QToolButton and that reimplements
QToolButton::setIconSet(), you should make the signature of the
reimplementation agree with the new QToolButton::setIconSet(),
a virtual function.
The global QTextStream manipulators setw(), setfill() and setprecison()
were renamed to qSetW(), qSetFill() and qSetPrecision() to avoid conflicts
with <iostream.h>. If you used them, you must rename the occurrences to
the new names.
The QTranslator class was extended in Qt 2.2, and these extensions
lead to a new interface. This interface is used mainly by translation
tools (for example, Qt
Linguist). For source compatibility, no member function was
effectively removed. The QTranslator documentation points out
which functions are obsolete.
This function is no longer virtual:
If you have a class that inherits QTranslator and which reimplements
QTranslator::find(), you should reimplement QTranslator::findMessage() instead.
In fact, find() is now defined in terms of findMessage(). By doing the
conversion, you will also gain support for translator comments and for any
future extensions.
QWidget::backgroundColor(), QWidget::setBackgroundColor(),
QWidget::backgroundPixmap() and QWidget::setBackgroundPixmap() have
often been the source of much confusion in previous releases. Qt 3.0
addresses this by obsoleting these functions and by remplacing them
with eight new functions: QWidget::eraseColor(),
QWidget::setEraseColor(), QWidget::erasePixmap(),
QWidget::setErasePixmap(), QWidget::paletteBackgroundColor(),
QWidget::setPaletteBackgroundColor(),
QWidget::paletteBackgroundPixmap() and
QWidget::setPaletteBackgroundPixmap(). See their documentation for
details.
The semantics of QXmlInputSource has changed slightly. This change
only affects code that parses the same data from the same input source
multiple times. In such cases you must call
QXmlInputSource::reset() before the second call to
QXmlSimpleReader::parse().
So code like
Due to some internal changes, it was necessary to clean-up the semantics of
QXmlLocator: this class is now an abstract class. This shouldn't cause
any problems, since programmers usually used the QXmlLocator that was
reported by QXmlContentHandler::setDocumentLocator(). If you used this
class in some other way, you must adjust your code to use the
QXmlLocator that is reported by the
QXmlContentHandler::setDocumentLocator() function.
QASyncIO, QDataSink, QDataSource, QIODeviceSource and QDataPump were
used internally in previous versions of Qt, but are not used anymore.
They are now obsolete.
In Qt 2.x, the AutoMask property was used to obtain a
transparent-looking widget. In general, this approach is slow and
processor hungry. Qt 3.0 uses the BackgroundOrigin which provides
vastly improved performance and more flexibility in most cases. The
few classes for which the AutoMask property is still the best approach
are QCheckBox, QComboBox, QPushButton, QRadioButton and QTabWidget.
The function names for Bezier curves in QPainter and QPointArray have
been corrected. They now properly reflect their cubic form instead of
a quadratic one. If you have been using either
QPainter::drawQuadBezier() or QPointArray::quadBezier() you must
replace these calls with
In Qt 2.x, QString only provided string comparisons using the Unicode
values of the characters of a string. This is efficient and reliable,
but it is not the appropriate order for most languages. For example,
French users expect 'é' (e acute) to be treated essentially as
'e' and not put after 'z'.
In Qt 3.0, QString::localeAwareCompare() implements locale aware
string comparisions on certain platforms. The classes QIconView, QListBox, QListView and QTable now use
QString::localeAwareCompare() instead of QString::compare(). If you
want to control the behaviour yourself you can always reimplement
QIconViewItem::compare(), QListBox::text(), QListViewItem::compare()
or QTableItem::key() as appropriate.
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