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This document describes porting applications from Qt 3 to Qt 4.
If you haven't yet made the decision about porting, or are unsure about whether it is worth it, take a look at the key features offered by Qt 4.
The Qt 4 series is not binary compatible with the 3 series. This means programs compiled for Qt 3 must be recompiled to work with Qt 4. Qt 4 is also not completely source compatible with 3, however nearly all points of incompatibility cause compiler errors or run-time messages (rather than mysterious results). Qt 4 includes many additional features and discards obsolete functionality. Porting from Qt 3 to Qt 4 is straightforward, and once completed makes the considerable additional power and flexibility of Qt 4 available for use in your applications.
To port code from Qt 3 to Qt 4:
Table of contents:
Qt 4 is the first version of Qt that contains no explicitly shared classes. All classes that were explicitly shared in Qt 3 are implicitly shared in Qt 4:
This means that if you took a copy of an instance of the class (using operator=() or the class's copy constructor), any modification to the copy would affect the original and vice versa. Needless to say, this behavior is rarely desirable.
Fortunately, nearly all Qt 3 applications don't rely on explicit sharing. When porting, you typically only need to remove calls to detach() and/or copy(), which aren't necessary anymore.
If you deliberately rely on explicit sharing in your application, you can use pointers or references to achieve the same result in Qt 4.
For example, if you have code like
void asciify(QByteArray array) { for (int i = 0; i < (int)array.size(); ++i) { if ((uchar)array[i] >= 128) array[i] = '?'; } }
you can rewrite it as
void asciify(QByteArray &array) { for (int i = 0; i < (int)array.size(); ++i) { if ((uchar)array[i] >= 128) array[i] = '?'; } }
(Notice the & in the parameter declaration.)
The QAccel class has been moved to the Qt 3 compatibility library. In new applications, you have three options:
The QAccel class also supported multiple accelerators using the same object, by calling QAccel::insertItem() multiple times. In Qt 4, the solution is to create multiple QShortcut objects.
The QApplication class has been split into two classes: QCoreApplication and QApplication. The new QApplication class inherits QCoreApplication and adds GUI-related functionality. In practice, this has no consequences for existing Qt applications.
In addition, the following API change was made:
Also, QWidgetList has changed from being a typedef for QPtrList<QWidget> to being a typedef for QList<QWidget *>. See the section on QWidgetList below for details.
For example, if you have code like
QWidgetList *list = QApplication::topLevelWidgets(); QWidgetListIt it(*list); QWidget *widget; while ((widget = it.current())) { if (widget->inherits("MainWindow")) ((MainWindow *)widget)->updateRecentFileItems(); ++it; } delete list;
you can rewrite it as
QWidgetList list = QApplication::topLevelWidgets(); for (int i = 0; i < list.size(); ++i) { if (MainWindow *mainWin = qt_cast<MainWindow>(list.at(i))) mainWin->updateRecentFileItems(); }
The QAquaStyle class first appeared in Qt 3.0, when the Qt/Mac port was first released. It emulated Apple's "Aqua" theme. In Qt 3.1, QAquaStyle was obsoleted by QMacStyle, which uses Appearance Manager to perform its drawing.
The QAquaStyle class is no longer provided in Qt 4. Use QMacStyle instead.
QAsciiCache<T> has been moved to the Qt 3 compatibility library. It has been replaced by QCache<QByteArray, T>.
For details, read the section on QCache<T>, mentally substituting QByteArray for QString.
QAsciiDict<T> and QAsciiDictIterator<T> have been moved to the Qt 3 compatibility library. They have been replaced by the more modern QHash<Key, T> and QMultiHash<Key, T> classes and their associated iterator classes.
When porting old code that uses QAsciiDict<T> to Qt 4, there are four classes that you can use:
For details, read the section on QDict<T>, mentally substituting QByteArray for QString.
The undocumented QBackInsertIterator class has been removed from the Qt library. If you need it in your application, feel free to copy the source code from the Qt 3 <qtl.h> header file.
In Qt 3, QBitArray inherited from QByteArray. In Qt 4, QBitArray is a totally independent class. This makes very little difference to the user, except that the new QBitArray doesn't provide any of QByteArray's byte-based API anymore. These calls will result in a compile-time error, except calls to QBitArray::truncate(), whose parameter was a number of bytes in Qt 3 and a number of bits in Qt 4.
QBitArray was an explicitly shared class in Qt 3. See Explicit Sharing for more information.
The QBitVal class has been renamed QBitRef.
The QButton class has been replaced by QAbstractButton in Qt 4. Classes like QPushButton and QRadioButton inherit from QAbstractButton. As a help when porting older Qt applications, the Qt 3 compatibility library contains a QButton class implemented in terms of the new QAbstractButton.
If you used the QButton class as a base class for your own button type and want to port your code to the newer QAbstractButton, you need to be aware that QAbstractButton has no equivalent for the QButton::drawButton(QPainter *) virtual function. The solution is to reimplement QWidget::paintEvent() in your QAbstractButton subclass as follows:
void MyButton::paintEvent(QPaintEvent *) { QPainter painter(this); drawButton(&painter); }
The QButtonGroup class has been completely redesigned in Qt 4. For compatibility, the old QButtonGroup class has been renamed Q3ButtonGroup and has been moved to the Qt 3 compatibility library, together with the QHButtonGroup and QVButtonGroup convenience subclasses.
Q3ButtonGroup could be used in two ways:
Unlike Q3ButtonGroup, the new QButtonGroup doesn't inherit QWidget. It is very similar to a "hidden Q3ButtonGroup".
If you use a Q3ButtonGroup, QHButtonGroup, or QVButtonGroup as a widget and want to port to Qt 4, you can replace it with QGroupBox. In Qt 4, radio buttons with the same parent are automatically part of an exclusive group, so you normally don't need to do anything else. See also the section on QGroupBox below.
In Qt 3, QByteArray was simply a typedef for QMemArray<char>. In Qt 4, QByteArray is a class in its own right, with a higher-level API in the style of QString.
Here are the main issues to be aware of when porting to Qt 4:
For example, if you have code like
QByteArray ba(64);
you can rewrite it as
QByteArray ba(64, '\0');
ba.at(0) = 'X';
will no longer compile. Instead, use QByteArray::operator[]:
ba[0] = 'X';
QByteArray was an explicitly shared class in Qt 3. See Explicit Sharing for more information.
QCache<T> has been renamed Q3Cache<T> and moved to the Qt 3 compatibility library. The new QCache class has a different API, and takes different template parameters: QCache<Key, T>.
When porting to Qt 4, QCache<QString, T> is the obvious substitute for Q3Cache<T>. The following table summarizes the API differences.
Q3Cache<T> function | QCache<QString, T> equivalent |
---|---|
Q3Cache::Q3Cache(int maxCost, int size, bool caseSensitive) | See remark below |
Q3Cache::autoDelete() | N/A |
Q3Cache::count() | QCache::count() or QCache::size() (equivalent) |
Q3Cache::setAutoDelete() | See remark below |
Q3Cache::size() | N/A |
Q3Cache::statistics() | N/A |
Q3Cache::operator=() | See remark below |
Remarks:
if (!cache.insert(key, object)) delete object;
becomes
cache.insert(key, object);
Q3Cache<QWidget> cache; cache.insert(widget->name(), widget); ... QWidget *foo = cache.take("foo"); if (foo) foo->show();
becomes
typedef QWidget *QWidgetPtr; QCache<QString, QWidgetPtr> cache; cache.insert(widget->name(), new QWidgetPtr(widget)); ... QWidgetPtr *ptr = cache.take("foo"); if (ptr) { QWidget *foo = *ptr; delete ptr; foo->show(); }
An alternative is to stick to using Q3Cache.
QCacheIterator<T> has been renamed Q3CacheIterator<T> and moved to the Qt 3 compatibility library. The new QCache class doesn't offer any iterator types.
The canvas module classes (QCanvas, QCanvasView, QCanvasItem,, QCanvasEllipse, QCanvasItemList, QCanvasLine, QCanvasPixmap, QCanvasPixmapArray, QCanvasPolygon, QCanvasPolygonalItem, QCanvasRectangle, QCanvasSpline, QCanvasSprite, and QCanvasText) have been moved to the Qt 3 compatibility library.
Qt 4 will provide a replacement module for these classes.
In Qt 3, a QPalette consisted of three QColorGroup objects. In Qt 4, the (rarely used) QColorGroup abstraction has been eliminated. For source compatibility, a QColorGroup class is available when QT_COMPAT is defined.
The new QPalette still works in terms of color groups, specified through enum values (QPalette::Active, QPalette::Disabled, and QPalette::Inactive). It also has the concept of a current color group, which you can set using QPalette::setCurrentColorGroup().
The QPalette object returned by QWidget::palette() returns a QPalette initialized with the correct current color group for the widget. This means that if you had code like
painter.setBrush(colorGroup().brush(QColorGroup::Background));
you can simply replace colorGroup() with palette():
painter.setBrush(palette().brush(QColorGroup::Background));
In Qt 3, QCString inherited from QByteArray. The main drawback of this approach is that the user had the responsibility of ensuring that the string is '\0'-terminated. Another important issue was that conversions between QCString and QByteArray often gave confusing results. (See the Achtung! Binary and Character Data article in Qt Quarterly for an overview of the pitfalls.)
Qt 4 solves that problem by merging the QByteArray and QCString classes into one class called QByteArray. Most functions that were in QCString previously have been moved to QByteArray. The '\0' issue is handled by having QByteArray allocate one extra byte that it always sets to '\0'. For example:
QByteArray ba("Hello"); ba.size(); // returns 5 (the '\0' is not counted) ba.length(); // returns 5 ba.data()[5]; // returns '\0'
The Qt 4 compatibility library contains a class called QCString that inherits from the new QByteArray class and that extends it to provide an API that is as close to the old QCString class as possible. Note that the following functions aren't provided by the compatibility QCString class:
The following functions have lost their last parameter, which specified whether the search was case sensitive or not:
In both cases, the solution is to convert the QCString to a QString and use the corresponding QString functions instead.
Also be aware that QCString::size() (inherited from QByteArray) used to return the size of the character data including the '\0'-terminator, whereas the new QByteArray::size() is just a synonym for QByteArray::length(). This brings QByteArray semantics in line with QString's.
When porting to Qt 4, occurrences of QCString should be replaced with QByteArray or QString. The following table summarizes the API differences between the QCString compatibility class and the Qt 4 QByteArray and QString classes:
QCString function | Qt 4 equivalent |
---|---|
QCString::QCString(const char *, uint) | See remark below |
QCString::QCString(int) | QByteArray::QByteArray(int, char) |
QCString::leftJustify() | QString::leftJustified() |
QCString::length() | QByteArray::length() or QByteArray::size() (equivalent) |
QCString::lower() | QByteArray::toLower() |
QCString::rightJustify() | QString::rightJustified() |
QCString::setExpand() | See remark below |
QCString::simplifyWhiteSpace() | QByteArray::simplified() |
QCString::sprintf() | QString::sprintf() |
QCString::stripWhiteSpace() | QByteArray::trimmed() |
QCString::toDouble() | QString::toDouble() |
QCString::toFloat() | QString::toFloat() |
QCString::toInt() | QString::toInt() |
QCString::toLong() | QString::toLong() |
QCString::toShort() | QString::toShort() |
QCString::toUInt() | QString::toUInt() |
QCString::toULong() | QString::toULong() |
QCString::toUShort() | QString::toUShort() |
QCString::upper() | QByteArray::toUpper() |
Remarks:
For example, if you have code like
QCString str1("Hello", 4); // "Hel" QCString str2("Hello world!", n);
you can rewrite it as
QByteArray str1("Hello", 3); QByteArray str2("Hello world!"); str2.truncate(n - 1);
For example, if you have code like
QCString str("Hello world"); str.setExpand(16, '\n'); // "Hello world \n"
you can rewrite it as
QCString str("Hello world"); while (str.size() < 16) str += ' '; str += '\n';
Since the old QCString class inherited from QByteArray, everything that is said in the QByteArray section applies for QCString as well.
The QDataBrowser class has been moved to the Qt 3 compatibility library.
See SQL Module for an overview of the new item SQL classes.
The QDataTable class has been moved to the Qt 3 compatibility library.
See SQL Module for an overview of the new item SQL classes.
The QDataView class has been moved to the Qt 3 compatibility library.
See SQL Module for an overview of the new item SQL classes.
The QDeepCopy<T> class in Qt 3 provided a means of ensuring that implicitly shared and explicitly shared classes referenced unique data. This was necessary because the reference counting in Qt's container classes was done in a thread-unsafe manner.
With Qt 4, QDeepCopy<T> has been moved to the Qt 4 compatibility library. Removing it from existing code is straightforward.
For example, if you have code like
QString str1 = "I am a string"; QDeepCopy<QString> str2 = str1; QString str3 = QDeepCopy<QString>(str2);
you can rewrite it as
QString str1 = "I am a string"; QString str2 = str1; QString str3 = str2;
QDict<T> has been moved to the Qt 3 compatibility library. It has been replaced by the more modern QHash<Key, T> and QMultiHash<Key, T> classes.
When porting old code that uses QDict<T> to Qt 4, there are four classes that you can use:
Qt 4 class | When to use it |
---|---|
QMultiHash<QString, T *> | Since QDict<T> is pointer-based and allows duplicate keys, this is usually the most straightforward conversion. |
QMultiHash<QString, T> | If type T is an assignable data type, you can use T as the value type rather than T *. This often leads to nicer code. |
QHash<QString, T *> | If you don't use duplicate keys, you can use QHash instead of QMultiHash. QMultiHash inherits from QHash. |
QHash<QString, T> |
The APIs of QDict<T> and QMultiHash<QString, T *> are quite similar. The main issue is that QDict supports auto-delete whereas QMultiHash doesn't. (See What's Wrong with Auto-Delete for an explanation of why the Qt 4 containers don't offer that feature.)
The following table summarizes the API differences between the two classes:
QDict function | QMultiHash equivalent |
---|---|
QDict::QDict(int size, bool caseSensitive) | See remarks below |
QDict::autoDelete() | N/A |
QDict::count() | QMultiHash::count() or QMultiHash::size() (equivalent) |
QDict::find(const QString &) | QMultiHash::value(const QString &) |
QDict::remove(const QString &) | QMultiHash::take(const QString &) |
QDict::resize(uint) | QMultiHash::reserve(int) |
QDict::setAutoDelete() | See discussion below |
QDict::size() | QMultiHash::capacity() |
QDict::statistics() | N/A |
QDict::operator[](const QString &) | See remark below |
Remarks:
If you use QDict's auto-delete feature (by calling QDict::setAutoDelete(true)), you need to do some more work. You have two options: Either you call delete yourself whenever you remove an item from the container, or you use QMultiHash<QString, T> instead of QMultiHash<QString, T *> (i.e. store values directly instead of pointers to values). Here, we'll see when to call delete.
The following table summarizes the idioms that you need to watch out for if you want to call delete yourself.
QDict idiom | QMultiHash idiom |
---|---|
dict.replace(key, value); | delete hash.take(key); hash.insert(key, value); |
dict.remove(key, value); | delete hash.take(key); |
dict.clear(); (also called from QDict's destructor) | while (!hash.isEmpty()) { T *value = *hash.begin(); dict.erase(hash.begin()); delete value; } In 99% of cases, the following idiom also works: qDeleteAll(hash); hash.clear(); However, it may lead to crashes if hash is referenced from the value type's destructor, because hash contains dangling pointers until clear() is called. |
Be aware that QDict's destructor automatically calls clear(). If you have a QDict data member in a custom class and use the auto-delete feature, you will need to call delete on all the items in the container from your class destructor to avoid a memory leak.
Finally, QDictIterator<T> must also be ported. There are no fewer than four iterator classes that can be used as a replacement: QHash::const_iterator, QHash::iterator, QHashIterator, and QHashMutableIterator. The most straightforward class to use when porting is QHashIterator<QString, T *>. The following table summarizes the API differences:
QDictIterator functions | Qt 4 equivalent |
---|---|
QDictIterator::count() | QHash::count() or QHash::size() |
QDictIterator::current() | QHashIterator::value() |
QDictIterator::currentKey() | QHashIterator::key() |
QDictIterator::isEmpty() | QHash::isEmpty() |
QDictIterator::toFirst() | QHashIterator::toFront() |
QDictIterator::operator()() | QHashIterator::value() |
QDictIterator::operator*() | QHashIterator::value() |
QDictIterator::operator++() | See remark below |
Be aware that QHashIterator has a different way of iterating than QDictIterator. A typical loop with QDictIterator looks like this:
QDictIterator<QWidget> i(dict); while (i.current() != 0) { do_something(i.currentKey(), i.current()); ++i; }
Here's the equivalent QHashIterator loop:
QHashIterator<QString, QWidget *> i(hash); while (i.hasNext()) { i.next(); // must come first do_something(i.key(), i.value()); }
See Java-style iterators for details.
QDir::encodedEntryList has been removed.
fileInfoList() and drives() now return a QList<QFileInfo> and not a QPtrList<QFileInfo> *. Code using these methods will have to be adapted.
Qt 3 used its own implementation of the DNS protocol and provided a low-level QDns class. Qt 4 uses the system's gethostbyname() function from a thread instead.
The old QDns class has been renamed Q3Dns and moved to the Qt 3 compatibility library. The new QDns class has a radically different API: It consists of two static functions, both called QDns::getHostByName(), one of which is blocking, the other non-blocking. See the QDns class documentation for details.
The QDropSite class has been obsolete ever since Qt 2.0. The only thing it does is call QWidget::setAcceptDrops(true).
For example, if you have code like
class MyWidget : public QWidget, public QDropSite { public: MyWidget(const QWidget *parent) : QWidget(parent), QDropSite(this) { } ... }
you can rewrite it as
class MyWidget : public QWidget { public: MyWidget(const QWidget *parent) : QWidget(parent) { setAcceptDrops(true); } ... }
The QEditorFactory class has been moved to the Qt 3 compatibility library.
See SQL Module for an overview of the new item SQL classes.
The QFileDialog class in Qt 4 has been totally rewritten. It provides most of the functionality of the old QFileDialog class, but with a different API. Some functionality, such as the ability to preview files, is expected to be added in a later Qt 4 release.
The old QFileDialog, QFileIconProvider, and QFilePreview classes has been renamed Q3FileDialog, Q3FileIconProvider, and Q3FilePreview and have been moved to the Qt 3 compatibility library. You can use them if you need some functionality not provided yet by the new QFileDialog class.
The following table lists which functions have been renamed or removed in Qt 4.
Remarks:
For example, if you have code like
fileDialog->addFilter(tr("JPEG files (*.jpg *.jpeg)"));
you can rewrite it as
QStringList filters = fileDialog->filters(); filters << tr("JPEG files (*.jpg *.jpeg)"); fileDialog->setFilters(filters);
For example, if you have code like
fileDialog->setSelectedFilter(3);
you can rewrite it as
fileDialog->selectFilter(fileDialog->filters().at(3));
The QFrame class has been made more lightweight in Qt 4, by reducing the number of properties and virtual functions. The reduction in the number of virtual functions is significant because QFrame is the base class of many Qt classes.
Here's an overview of the changes:
As an help to porting, the Qt 3 compatibility library contains a Q3Frame class that inherits QFrame and provides a similar API to the old QFrame class. If you derived from QFrame in your application, you might want to use Q3Frame as a base class as a first step in the porting process, and later move on to the new QFrame class.
This class no longer inherits from QNetworkProtocol. See the section on QNetworkProtocol for details.
The QGrid class has been renamed QGridWidget.
The QGroupBox class has been redesigned in Qt 4. The old QUrl class has been renamed Q3GroupBox and moved to the Qt 3 compatibility library.
The new QGroupBox is more lightweight. It doesn't attempt to duplicate functionality already provided by QGridLayout. For that reason, the following members have been removed:
Naturally, the columns and orientation properties have also been removed.
If you rely on some of the missing functionality in your application, you can use Q3GroupBox instead of QGroupBox as a help to porting.
The QGuardedPtr<T> class has been renamed QPointer<T> in Qt 4. The Qt 3 compatibility library contains a trivial implementation of QGuardedPtr<T> in terms of QPointer<T>.
The QHBox class has been renamed QHBoxWidget.
This class no longer inherits from QNetworkProtocol. See the See the section on QNetworkProtocol for details.
The QIconFactory is no longer part of Qt. It has been replaced by a lighter mechanism based on function pointers.
To port old code that uses QIconFactory to Qt 4, you generally need to turn your QIconFactory::createPixmap() reimplementation into a regular function and call QIconSet::setPixmapGeneratorFn() or QIconSet::setDefaultPixmapGeneratorFn() on it.
The QIconView, QIconViewItem, QIconDrag, QIconDragItem classes has been moved to the Qt 3 compatibility library. New Qt applications should use QListWidget or its base class QListView instead, and call QListView::setViewMode(QListView::IconMode) to obtain an "icon view" look.
See Model-View Programming for an overview of the new item view classes.
QImage::fromMimeSource(const QString &) -> qImageFromMimeSource(const QString &)
QIntCache<T> has been moved to the Qt 3 compatibility library. It has been replaced by QCache<int, T>.
For details, read the section on QCache<T>, mentally substituting int for QString.
QIntDict<T> and QIntDictIterator<T> have been moved to the Qt 3 compatibility library. They have been replaced by the more modern QHash<Key, T> and QMultiHash<Key, T> classes and their associated iterator classes.
When porting old code that uses QIntDict<T> to Qt 4, there are four classes that you can use:
For details, read the section on QDict<T>, mentally substituting int for QString.
Virtuals readBlock and writeBlock now accept a Q_LONG length argument (rather than a Q_ULONG). All subclass will need to change as this is a pure virtual function build errors will occur.
The QListBox, QListBoxItem, QListBoxText, and QListBoxPixmap classes have been moved to the Qt 3 compatibility library. New Qt applications should use QListWidget or its base class QListView instead.
See Model-View Programming for an overview of the new item view classes.
The QListView, QListViewItem, QCheckListItem, and QListViewItemIterator classes have been renamed Q3ListView, Q3ListViewItem, Q3CheckListItem, and Q3ListViewItemIterator, and have been moved to the Qt 3 compatibility library. New Qt applications should use one of the following four classes instead: QTreeView or QTreeWidget for tree-like structures; QListWidget or the new QListView class for one-dimensional lists.
See Model-View Programming for an overview of the new item view classes.
The QLocalFs class is no longer part of the public Qt API. It has been moved to the Qt 3 compatibility library. Use QDir, QFileInfo, or QFile instead.
QMemArray<T> has been moved to the Qt 3 compatibility library. It has been replaced by the QVector<T> class.
The following table summarizes the API differences between the two classes.
QMemArray::assign(const QMemArray<T> &) | QVector::operator=() |
QMemArray::assign(const T *, uint) | See remark below |
QMemArray::duplicate(const QMemArray &) | QVector::operator=() |
QMemArray::duplicate(const T *, uint) | See remark below |
QMemArray::setRawData(const T *, uint) | N/A |
QMemArray::resetRawData(const T *, uint) | N/A |
QMemArray::find(const T &, uint) | QVector::indexOf(const T &, int) |
QMemArray::contains(const T &) | QVector::count(const T &) |
QMemArray::sort() | qHeapSort() |
QMemArray::bsearch(const T &d) | qBinaryFind() |
QMemArray::at(uint) | QVector::operator[]() |
QMemArray::operator const T *() | QVector::constData() |
Remarks:
For example, if you have code like
QMemArray<QSize> array; ... array.assign(data, size);
you can rewrite it as
QVector<QSize> vector; ... vector.resize(size); qCopy(data, data + size, vector.begin());
The QMimeSourceFactory has been moved to the Qt 3 compatibility library. New Qt applications should use Qt 4's Resource System instead.
The QMultiLineEdit class in Qt 3 was a convenience QTextEdit subclass that provided an interface compatible with Qt 2's QMultiLineEdit class. In Qt 4, it inherits Q3TextEdit and is part of the Qt 3 compatibility library. Use QTextEdit in new code.
The QNetworkProtocol, QNetworkProtocolFactoryBase, QNetworkProtocolFactory<T>, and QNetworkOperation classes are no longer part of the public Qt API. They have been moved to the Qt 3 compatibility library.
In Qt 4 applications, you can use classes like QFtp and QHttp directly to perform file-related actions on a remote host.
children() and QueryList now return a QObjectList instead of a pointer to a QObjectList. See also the comments on QObjectList.
killTimers() has been removed.
The QObjectDictionary class is a synonym for QAsciiDict<QMetaObject>. See the section on QAsciiDict<T>.
In Qt 3, the QObjectList class was a typedef for QPtrList<QObject>. In Qt 4, it is a typedef for QList<QObject *>. See the section on QPtrList<T>.
To reimplement painter backends one previously needed to reimplement the virtual function QPaintDevice::cmd(). This function is taken out and should is replaced with the function QPaintDevice::paintEngine() and the abstract class QPaintEngine. QPaintEngine provides virtual functions for all drawing operations that can be performed on a painter backend.
bitBlt and copyBlt are now only compatibility functions. Use QPainter and drawPixmap instead.
Probably something needs to be said about new stuff from painting? Don't know, I didn't do that part.
QPicture::copy() is deprecated and QPicture::detach() is now a public internal function. In general, one should have never needed to call these functions.
QPixmap::fromMimeSource(const QString &) -> qPixmapFromMimeSource(const QString &)
In Qt 3, QPointArray inherited from QMemArray<QPoint>. In Qt 4, it inherits from QVector<QPoint>. Everything mentioned in the section on QMemArray<T> apply for QPointArray as well.
The QPointArray::setPoints() and QPointArray::putPoints() functions returned a bool in Qt 3, indicating whether the array was successfully resized or not. In Qt 4, they return void.
page setup / print setup -> Use QPrintDialog, QPageSetupDialog Compat functions: margins Killed -> setMargins
The QPtrCollection<T> abstract base class has been moved to the Qt 3 compatibility library. There is no direct equivalent in Qt 4.
QPtrDict<T> and QPtrDictIterator<T> have been moved to the Qt 3 compatibility library. They have been replaced by the more modern QHash<Key, T> and QMultiHash<Key, T> classes and their associated iterator classes.
When porting old code that uses QPtrDict<T> to Qt 4, there are four classes that you can use:
(You can naturally use other types than void * for the key type, e.g. QWidget *.)
To port QPtrDict<T> to Qt 4, read the section on QDict<T>, mentally substituting void * for QString.
QPtrList<T>, QPtrListIterator<T>, and QPtrListStdIterator<T> have been moved to the Qt 3 compatibility library. They have been replaced by the more modern QList and QLinkedList classes and their associated iterator classes.
When porting to Qt 4, you have the choice of using QList<T> or QLinkedList<T> as alternatives to QValueList<T>. QList<T> has an index-based API and provides very fast random access (QList::operator[]), whereas QLinkedList<T> has an iterator-based API.
The following table summarizes the API differences between QPtrList<T> and QList<T *>:
QPtrList function | QList equivalent |
---|---|
QPtrList::contains(const T *) | QList::count(T *) |
QPtrList::containsRef(const T *) | QList::count(T *) |
QPtrList::find(const T *) | See remark below |
QPtrList::findRef(const T *) | See remark below |
QPtrList::getFirst() | QList::first() |
QPtrList::getLast() | QList::last() |
QPtrList::inSort(const T *) | N/A |
QPtrList::remove(const T *) | QList::removeAll(T *) |
QPtrList::remove(uint) | QList::removeAt(int) |
QPtrList::removeNode(QLNode *) | N/A |
QPtrList::removeRef(const T *) | QList::removeAll(T *) |
QPtrList::sort() | See remark below |
QPtrList::takeNode(QLNode *) | N/A |
QPtrList::toVector(QGVector *) | See remark below |
Remarks:
For example, if you have code like
QPtrList<QWidget> list; ... QPtrVector<QWidget> vector; list.toVector(&vector);
you can rewrite it as
QList<QWidget *> list; ... QVector<QWidget *> vector; vector.resize(list.size()); qCopy(list.begin(), list.end(), vector.begin());
If you use QPtrList's auto-delete feature (by calling QPtrList::setAutoDelete(true)), you need to do some more work. You have two options: Either you call delete yourself whenever you remove an item from the container, or you can use QList<T> instead of QList<T *> (i.e. store values directly instead of pointers to values). Here, we'll see when to call delete. (See What's Wrong with Auto-Delete for an explanation of why the Qt 4 containers don't offer that feature.)
The following table summarizes the idioms that you need to watch out for if you want to call delete yourself.
QPtrList idiom | QList idiom |
---|---|
list.replace(index, value); | delete list[index]; list[index] = value; |
list.removeFirst(); | delete list.takeFirst(); |
list.removeLast(); | delete list.takeLast(); |
list.remove(index); | delete list.take(index); |
list.remove(value); | int i = list.indexOf(value); if (i != -1) delete list.takeAt(i); |
list.remove(); (removes the current item) | QListMutableIterator<T *> i; ... delete i.value(); i.remove(); |
list.clear(); (also called from QPtrList's destructor) | while (!list.isEmpty()) delete list.takeFirst(); In 99% of cases, the following idiom also works: qDeleteAll(list); list.clear(); However, it may lead to crashes if list is referenced from the value type's destructor, because list contains dangling pointers until clear() is called. |
Be aware that QPtrList's destructor automatically calls clear(). If you have a QPtrList data member in a custom class and use the auto-delete feature, you will need to call delete on all the items in the container from your class destructor to avoid a memory leak.
QPtrList had the concept of a "current item", which could be used for traversing the list without using an iterator. When porting to Qt 4, you can use the Java-style QListIterator<T *> (or QListMutableIterator<T *>) class instead. The following table summarizes the API differences:
QPtrList function | QListIterator equivalent |
---|---|
QPtrList::at() | N/A |
QPtrList::current() | QListIterator::value() |
QPtrList::currentNode() | N/A |
QPtrList::findNext(const T *) | QListIterator::findNext(const T *) |
QPtrList::findNextRef(const T *) | QListIterator::findNext(const T *) |
QPtrList::first() | QPtrList::toFront() |
QPtrList::last() | QPtrList::toBack() |
QPtrList::next() | QPtrList::next() |
QPtrList::prev() | QPtrList::previous() |
QPtrList::remove() | QListMutableIterator::remove() |
QPtrList::take() | QListMutableIterator::remove() |
Be aware that QListIterator has a different way of iterating than QPtrList. A typical loop with QPtrList looks like this:
QPtrList<QWidget> list; ... while (list.current() != 0) { do_something(list.current()); list.next(); }
Here's the equivalent QListIterator loop:
QList<QWidget *> list; ... QListIterator<QWidget *> i(list); while (i.hasNext()) do_something(i.next());
Finally, QPtrListIterator<T> must also be ported. There are no fewer than four iterator classes that can be used as a replacement: QList::const_iterator, QList::iterator, QListIterator, and QListMutableIterator. The most straightforward class to use when porting is QListMutableIterator<T *> (if you modify the list through the iterator) or QListIterator<T *> (if you don't). The following table summarizes the API differences:
QPtrListIterator function | Qt 4 equivalent |
---|---|
QPtrListIterator::atFirst() | !QListIterator::hasPrevious() (notice the !) |
QPtrListIterator::atLast() | !QListIterator::hasNext() (notice the !) |
QPtrListIterator::count() | QList::count() or QList::size() |
QPtrListIterator::current() | QListIterator::value() |
QPtrListIterator::isEmpty() | QList::isEmpty() |
QPtrListIterator::toFirst() | QListIterator::toFront() |
QPtrListIterator::toLast() | QListIterator::toBack() |
QPtrListIterator::operator() | QListIterator::value() |
QPtrListIterator::operator*() | QListIterator::value() |
Again, be aware that QListIterator has a different way of iterating than QPtrList. A typical loop with QPtrList looks like this:
QPtrList<QWidget> list; ... QPtrListIterator<QWidget> i; while (i.current() != 0) { do_something(i.current()); i.next(); }
Here's the equivalent QListIterator loop:
QList<QWidget *> list; ... QListIterator<QWidget *> i(list); while (i.hasNext()) do_something(i.next());
Finally, QPtrListStdIterator<T> must also be ported. This is easy, because QList also provides STL-style iterators (QList::iterator and QList::const_iterator).
QPtrQueue has been moved to the Qt 3 compatibility library. It has been replaced by the more modern QQueue class.
The following table summarizes the differences between QPtrQueue<T> and QQueue<T *>:
QPtrQueue function | QQueue equivalent |
---|---|
QPtrQueue::autoDelete() | See discussion below |
QPtrQueue::count() | QQueue::count() or QQueue::size() (equivalent) |
QPtrQueue::current() | QQueue::head() |
QPtrQueue::remove() | QQueue::dequeue() |
QPtrQueue::setAutoDelete() | See discussion below |
If you use QPtrQueue's auto-delete feature (by calling QPtrQueue::setAutoDelete(true)), you need to do some more work. You have two options: Either you call delete yourself whenever you remove an item from the container, or you can use QQueue<T> instead of QQueue<T *> (i.e. store values directly instead of pointers to values). Here, we will show when to call delete. (See What's Wrong with Auto-Delete for an explanation of why the Qt 4 containers don't offer that feature.)
QPtrQueue idiom | QQueue idiom |
---|---|
queue.dequeue(); | delete queue.dequeue(); |
queue.remove(); | delete queue.dequeue(); |
queue.clear(); (also called from QPtrQueue's destructor) | while (!queue.isEmpty()) delete queue.dequeue(); In 99% of cases, the following idiom also works: qDeleteAll(queue); queue.clear(); However, it may lead to crashes if queue is referenced from the value type's destructor, because queue contains dangling pointers until clear() is called. |
QPtrStack has been moved to the Qt 3 compatibility library. It has been replaced by the more modern QStack class.
The following table summarizes the differences between QPtrStack<T> and QStack<T *>:
QPtrStack function | QStack equivalent |
---|---|
QPtrStack::autoDelete() | See discussion below |
QPtrStack::count() | QStack::count() or QStack::size() (equivalent) |
QPtrStack::current() | QStack::top() |
QPtrStack::remove() | QStack::pop() |
QPtrStack::setAutoDelete() | See discussion below |
If you use QPtrStack's auto-delete feature (by calling QPtrStack::setAutoDelete(true)), you need to do some more work. You have two options: Either you call delete yourself whenever you remove an item from the container, or you can use QStack<T> instead of QStack<T *> (i.e. store values directly instead of pointers to values). Here, we will show when to call delete. (See What's Wrong with Auto-Delete for an explanation of why the Qt 4 containers don't offer that feature.)
QPtrStack idiom | QStack idiom |
---|---|
stack.pop(); | delete stack.pop(); |
stack.remove(); | delete stack.pop(); |
stack.clear(); (also called from QPtrStack's destructor) | while (!stack.isEmpty()) delete stack.pop(); In 99% of cases, the following idiom also works: qDeleteAll(stack); stack.clear(); However, it may lead to crashes if stack is referenced from the value type's destructor, because stack contains dangling pointers until clear() is called. |
QPtrVector<T> has been moved to the Qt 3 compatibility library. It has been replaced by the more modern QVector class.
When porting to Qt 4, you can use QVector<T *> as an alternative to QPtrVector<T>. The APIs of QPtrVector<T> and QVector<T *> are somewhat similar. The main issue is that QPtrVector supports auto-delete whereas QVector doesn't. (See What's Wrong with Auto-Delete for an explanation of why the Qt 4 containers don't offer that feature.)
The following table summarizes the API differences between the two classes:
QPtrVector function | QVector equivalent |
---|---|
QPtrVector::autoDelete() | See discussion below |
QPtrVector::bsearch(const T *) | qBinaryFind() |
QPtrVector::contains(const T *) | QVector::count(T *) |
QPtrVector::containsRef(const T *) | QVector::count(T *) |
QPtrVector::count() | See remark below |
QPtrVector::insert(uint, T *) | See remark below |
QPtrVector::isNull() | N/A |
QPtrVector::remove(uint) | See remark below |
QPtrVector::setAutoDelete() | See discussion below |
QPtrVector::sort() | qHeapSort() |
QPtrVector::take(uint) | See remark below |
QPtrVector::toList(QGList *) | QList::QList(const QVector &) |
Remarks:
For example, if you have code like
int numValidItems = vect.count();
you can rewrite it as
int numValidItems = vect.size() - vect.count(0);
If you use QVector's auto-delete feature (by calling QVector::setAutoDelete(true)), you need to do some more work. You have two options: Either you call delete yourself whenever you remove an item from the container, or you use QVector<T> instead of QVector<T *> (i.e. store values directly instead of pointers to values). Here, we'll see when to call delete.
The following table summarizes the idioms that you need to watch out for if you want to call delete yourself.
QPtrVector idiom | QVector idiom |
---|---|
vect.insert(i, ptr); | delete vect[i]; vect[i] = ptr; |
vect.remove(i); | delete vect[i]; vect[i] = 0; |
T *ptr = vect.take(i); | T *ptr = vect[i]; vect[i] = 0; |
vect.resize(n) | while (n > vect.size()) vect.append(0); while (n < vect.size() { T *ptr = vect.last(); vect.remove(vect.size() - 1); delete ptr; } |
vect.clear(); (also called from QPtrVector's destructor) | for (int i = 0; i < vect.size(); ++i) T *ptr = vect[i]; vect[i] = 0; delete ptr; } In 99% of cases, the following idiom also works: qDeleteAll(vect); vect.clear(); However, it may lead to crashes if vect is referenced from the value type's destructor, because vect contains dangling pointers until clear() is called. |
Be aware that QPtrVector's destructor automatically calls clear(). If you have a QPtrVector data member in a custom class and use the auto-delete feature, you will need to call delete on all the items in the container from your class destructor to avoid a memory leak.
In Qt 3, various "range control" widgets (QDial, QScrollBar, QSlider, and QSpinBox) inherited from both QWidget and QRangeControl.
In Qt 4, QRangeControl has been replaced with the new QAbstractSlider class, which inherits from QWidget and provides similar functionality. Apart from eliminating unnecessary multiple inheritance, the new design allows QAbstractSlider to contain signals, slots, and properties.
The old QRangeControl class has been moved to the Qt 3 compatibility library, together with the (undocumented) QSpinWidget class.
If you use QRangeControl as a base class in your application, you can switch to use QAbstractSlider instead.
For example, if you have code like
class VolumeControl : public QWidget, public QRangeControl { ... protected: void valueChange() { update(); emit valueChanged(value()); } void rangeChange() { update(); } void stepChange() { update(); } };
you can rewrite it as
class VolumeControl : public QAbstractSlider { ... protected: void sliderChange(SliderChange change) { update(); if (change == SliderValueChange) emit valueChanged(value()); } };
The following changes have been made to QRegion in Qt 4:
The QScrollView class has been moved to the Qt 3 compatibility library. It has been replaced by the QViewport and QWidgetView classes.
QScrollView was designed to work around the 16-bit limitation on widget coordinates found on most window systems. In Qt 4, this is done transparently for all widgets, so there is no longer a need for such functionality in QScrollView. For that reason, the new QViewport and QWidgetView classes are much more lightweight, and concentrate on handling scroll bars.
If you used QScrollView as a base class
The QShared class has been obsoleted by the more powerful QSharedData and QSharedDataPointer as a means of creating custom implicitly shared classes. It has been moved to the Qt 3 compatibility library.
An easy way of porting to Qt 4 is to include this class into your project and to use it instead of QShared:
struct Shared { Shared() : count(1) {} void ref() { ++count; } bool deref() { return !--count; } uint count; };
If possible, we recommend that you use QSharedData and QSharedDataPointer instead. They provide thread-safe reference counting and handle all the reference counting behind the scenes, eliminating the risks of forgetting to increment or decrement the reference count.
The QSignal class has been completely redesigned in Qt 4. For compatibility, the old QSignal class has been renamed Q3Signal and has been moved to the Qt 3 compatibility library.
The new QSignal class is a template class, where the template type gives the parameter type of the signal. For example, if you used Q3Signal class's @C{intSignal(int)} signal, you can now use QSignal<int>'s @C{signal(int)} signal instead.
The Q3Signal::setParameter(), Q3Signal::parameter(), Q3Signal::setValue(), and Q3Signal::value() functions have no direct equivalent in Qt 4. Instead, pass the value to QSignal::activate().
For example, if you have code like
QSignal signal; signal.connect(target, SLOT(display(int))); ... signal.setParameter(5); signal.activate();
you can rewrite it as
QSignal<int> signal; signal.connect(target, SLOT(display(int))); ... signal.activate(5);
The QSlider::sliderStart() and QSlider::sliderRect() functons have been removed. You can retrieve this information using QAbstractSlider::sliderPosition() and QStyle::querySubControlMetrics(), respectively.
The QSortedList<T> class has been deprecated since Qt 3.0. In Qt 4, it has been moved to the Qt 3 compatibility library.
In new code, we recommend that you use QList<T> instead and use qHeapSort() to sort the items.
The function setResizeMode() has been moved into compat. Set the stretch factor in the widget's size policy to get equivalent functionality.
The obsolete function drawSplitter() has been removed. Use QStyle::drawPrimitive() to acheive similar functionality.
The QSqlCursor class has been moved to the Qt 3 compatibility library.
See SQL Module for an overview of the new item SQL classes.
QSqlDatabase is now a smart pointer that is passed around by value. Simply replace all QSqlDatabase pointer by QSqlDatabase objects.
The QSqlEditorFactory class has been moved to the Qt 3 compatibility library.
See SQL Module for an overview of the new item SQL classes.
The enum Type was renamed to ErrorType, The values were renamed as well:
The QSqlFieldInfo class has been moved to the Qt 3 compatibility library. Its functionality is now provided by the QSqlField class.
See SQL Module for an overview of the new item SQL classes.
The QSqlForm class has been moved to the Qt 3 compatibility library.
See SQL Module for an overview of the new item SQL classes.
The QSqlPropertyMap class has been moved to the Qt 3 compatibility library.
See SQL Module for an overview of the new item SQL classes.
QSqlQuery::prev() was renamed to QSqlQuery::previous(). There is a function call for compatibility, but if you subclassed QSqlQuery, you have to reimplement previous() instead of prev().
QSqlRecord behaves like a vector now, QSqlRecord::insert() will actually insert a new field instead of replacing the existing one.
The QSqlRecordInfo class has been moved to the Qt 3 compatibility library. Its functionality is now provided by the QSqlRecord class.
See SQL Module for an overview of the new item SQL classes.
The QSqlSelectCursor class has been moved to the Qt 3 compatibility library.
See SQL Module for an overview of the new item SQL classes.
The QStrList and QStrIList convenience classes have been deprecated since Qt 2.0. In Qt 4, they have been moved to the Qt 3 compatibility library. If you used any of these, we recommend that you use QStringList or QList<QByteArray> instead.
The QStrVec and QStrIVec convenience classes have been deprecated since Qt 2.0. In Qt 4, they have been moved to the Qt 3 compatibility library. If you used any of these, we recommend that you use QStringList or QList<QByteArray> instead.
Here are the main issues to be aware of when porting QString to Qt 4:
For example, if you have code like
str1 = QString::null; if (str2 == QString::null) do_something(QString::null);
you can rewrite it as
str1.clear(); if (str2.isNull()) do_something(QString());
str.at(0) = 'X';
will no longer compile. Instead, use QString::operator[]:
str[0] = 'X';
For example, if you have code like
if (url.startsWith("http:", false)) ...
you can rewrite it as
if (url.startsWith("http:", Qt::CaseInsensitive)) ...
For example, if you have code like
str.setExpand(32, '$');
you can rewrite it as
str[32] = '$';
QStringList now inherits from QList<QString> and can no longer be converted to a QValueList<QString>. Since QValueList inherits QList a cast will work as expected.
This change implies some API incompatibilities for QStringList. For example, at() returns the string, not an iterator. See the section on QValueList for details.
The QTabDialog class is no longer part of the public Qt API. It has been moved to the Qt 3 compatibility library. In Qt 4 applications, you can easily obtain the same result by combining a QTabWidget with a QDialog and provide QPushButtons yourself.
The QTable, QTableItem, QComboTableItem, QCheckTableItem, and QTableSelection classes have been moved to the Qt 3 compatibility library. New Qt applications should use the new QTableWidget or QTableView class instead.
See Model-View Programming for an overview of the new item view classes.
The undocumented QTextOStreamIterator class has been removed from the Qt library. If you need it in your application, feel free to copy the source code from the Qt 3 <qtl.h> header file.
The QUrl class has been rewritten from scratch in Qt 4 to be more standard-compliant. The old QUrl class has been renamed Q3Url and moved to the Qt 3 compatibility library.
The new QUrl class provides an extensive list of compatibility functions to ease porting from Q3Url to QUrl. A few functions require you to change your code:
The QUrlOperator class is no longer part of the public Qt API. It has been moved to the Qt 3 compatibility library.
In Qt 4 applications, you can use classes like QFtp and QHttp directly to perform file-related actions on a remote host.
The QValueList<T> class has been replaced by QList<T> and QLinkedList<T> in Qt 4. As a help when porting older Qt applications, the Qt 3 compatibility library contains a QValueList<T> class implemented in terms of the new QLinkedList<T>. Similarly, it contains QValueListIterator<T> and QValueListConstIterator<T> classes implemented in terms of QLinkedList<T>::iterator and QLinkedList<T>::const_iterator.
When porting to Qt 4, you have the choice of using QList<T> or QLinkedList<T> as alternatives to QValueList<T>. QList<T> has an index-based API and provides very fast random access (QList::operator[]), whereas QLinkedList<T> has an iterator-based API.
Here's a list of problem functions:
For example, if you have code like
for (QValueList<T>::iterator i = list.fromLast(); i != list.end(); ++i) do_something(*i);
you can rewrite it as
QLinkedList<T>::iterator i = list.end(); while (i != list.begin()) { --i; // decrement i before using it do_something(*i); }
The QValueVector<T> class has been replaced by QVector<T> in Qt 4. As a help when porting older Qt applications, the Qt 3 compatibility library contains a QValueVector<T> class implemented in terms of the new QVector<T>.
When porting from QValueVector<T> to QVector<T>, you might run into the following incompatibilities:
See Generic Containers for an overview of the Qt 4 container classes.
The QVariant class has been split into two classes: QCoreVariant and QVariant. The new QVariant class inherits QCoreVariant and adds GUI-related types. In practice, this has no consequences for existing Qt applications.
In addition, some changes to the rest of the Qt library have implications on QVariant as well:
The QVBox class has been renamed QVBoxWidget.
Widget background painting has been greatly improved, supporting flickerfree updates and making it possible to have half transparent widgets. This renders the following background handling functions obsolete:
A widget now receives change events in its QWidget::changeEvent() handler. This makes the following virtual change handlers obsolete:
The following functions were slots, but are no more:
The following functions were incorrectly marked as virtual:
The QWidgetIntDict class was a synonym for QIntDict<QWidget>. It is no longer available in Qt 4. If you link against the Qt 3 compatibility library, you can use QIntDict<QWidget> instead; otherwise, see the section on QDict<T>.
In Qt 3, the QWidgetList class was a typedef for QPtrList<QWidget>. In Qt 4, it is a typedef for QList<QWidget *>. See the section on QPtrList<T>.
The QWidgetStack class is no longer part of the Qt public API. It has been moved to the Qt 3 compatibility library.
In Qt 4 applications, you can use QStackedLayout instead to obtain the same results.
The QWizard class is no longer part of the Qt public API. It has been moved to the Qt 3 compatibility library. In Qt 4 applications, you can easily obtain the same result by combining a QStackedBox with a QDialog and provide QPushButtons yourself.
The dialogs/simplewizard and dialogs/complexwizard examples show how to create wizards without using QWizard.
Copyright © 2004 Trolltech. | Trademarks | Qt 4.0.0-tp2 |