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/****************************************************************************
**
** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/legal
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
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** this file. Please review the following information to ensure
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****************************************************************************/
/*!
\page qtquick-porting-qt5.html
\title Porting QML Applications to Qt 5
\brief Lists the Qt 5.0 changes that affect the existing QML applications
When porting QML-related code from Qt 4.8 to Qt 5, application developers should be aware that
the QML infrastructure has undergone considerable changes in Qt 5. The sections below describe
these changes and the impact they have on your existing code.
This article describes the changes that affect your existing code. If you are
interested in the summary of all new features in Qt 5 for QML application development, see
\l{Qt QML Release Notes} and \l{Qt Quick Release Notes}.
\section1 QML Language Changes
There are very few changes in the QML language that affect the porting of existing Qt 4.8 QML code to Qt 5. These are:
\list
\li Individual file imports no longer work (for example, import "MyType.qml"). Import the containing directory instead.
\li Relative file paths in JavaScript files are now resolved relative to the location of the JavaScript file instead of the QML file that imported it.
\li It's no longer possible to override signals from the base component.
\endlist
\section1 QtQuick Module
The QtQuick module has been updated to version 2. All QML applications should update their import
statements to use the new version:
\code
import QtQuick 2.3
\endcode
\section2 Property and Method Changes
\list
\li ListView's \c highlightMoveSpeed and \c highlightResizeSpeed properties have been renamed to
\l{ListView::}{highlightMoveVelocity} and \l{ListView::}{highlightResizeVelocity}, respectively.
\li TextInput and TextEdit's \c openSoftwareInputPanel() and \c closeSoftwareInputPanel() methods
have been removed. Use the new Qt.inputMethod property and call Qt.inputMethod.show()
Qt.inputMethod.hide() to show and hide the virtual keyboard.
\endlist
\section2 Type and API Changes
\list
\li XmlListModel has moved into its own module, QtQuick.XmlListModel. Any code that uses the
XmlListModel and XmlRole types must import \e {QtQuick.XmlListModel} instead.
\li The local storage API that enables SQL support has been moved from the \l {QML Global Object}
into a \c QtQuick.LocalStorage singleton type. Any code that requires the local storage API must import
\e {QtQuick.LocalStorage} instead. See the \l {QtQuick.LocalStorage}{Qt Quick Local Storage} documentation
for examples.
\li The \c LayoutItem type has been removed from the \c QtQuick module as it was specific to the
Graphics View framework backend used in \l {Qt Quick 1}.
\endlist
\section2 Behavioral Changes
QtQuick 2 includes a number of behavioral changes and you should thoroughly test your applications after
porting. These changes will not necessarily lead to run-time errors, but may break certain assumptions in your code.
Below are the prominent changes to be aware of when porting your applications.
Item opacity and visibility:
\list
\li The input handling details of \l{Item::}{opacity} and \l{Item::}{visible} have changed. An opacity of zero no
longer affects input handling, where previously it stopped mouse input. A visibility of false no longer affects
keyboard input, but still stops mouse input. The new \l{Item::}{enabled} property stops mouse and keyboard input, but does not affect how or whether
the item is rendered. A workaround for applying the old behavior in most cases is to bind enabled to
\tt {(visible && opacity > 0.0)}.
\li Previously, if an item was in a positioner (i.e. a \l Row, \l Column, \l Grid and \l Flow)
and the item's \c opacity changed to 0, or its \c visible value became \c false, the positioner
would remove the item from its layout and collapse the space for that item. In QtQuick 2, this
now only happens when an item's \c visible is \c false; the item opacity no longer affects whether
the item is laid out. (This is consistent with the existing behavior of ListView and GridView).
\endlist
Text:
\list
\li The TextEdit::textFormat property now defaults to \c PlainText instead of \c AutoText.
\li When Text::textFormat is set to \c Text.AutoText format, the text object will automatically
switch to \c Text.StyledText instead of \c Text.RichText.
\endlist
Other:
\list
\li Modifying the Image::sourceSize now fits the image to the size, maintaining aspect
ratio.
\li For ListView and GridView, the \c cacheBuffer property now has a non-zero default and
delegates in the cache buffer are created asynchronously. Also, using a \c RightToLeft layout
now also reverses the \c preferredHighlightBegin and \c preferredHighlightEnd.
\li For \l Loader, the \c sourceChanged and \c sourceComponentChanged signals are now only emitted
when their respective properties change value. (Previously \l Loader emitted both of these signals
when either of the relevant properties had changed.)
\endlist
\section2 Changes to experimental Qt.labs modules
\list
\li The \c Qt.labs.particles module has been removed. It is replaced by the fully-fledged \l
QtQuick.Particles module which is an enormous improvement on its predecessor.
\li The \c Qt.labs.shaders module has been removed as the \c ShaderEffectItem and \l
ShaderEffectSource types from this module have been moved into the \c QtQuick module. Note the \c
ShaderEffectItem type has been renamed to \l ShaderEffect.
\endlist
\section1 C++ code
In Qt 5, all QML applications are rendered with an OpenGL scenegraph architecture rather than the
Graphics View framework used in Qt 4. Due to the scale of this architectural change, the C++ API has
been extensively restructured and the \c QtDeclarative module has been deprecated in favor of two
new modules: \l {Qt QML}, which implements the QML engine and language infrastructure, and \l {Qt Quick},
which implements the visual canvas and scenegraph backend.
All classes that were previously in the \c QtDeclarative module have been moved into the \l {Qt QML}
and \l {Qt Quick} modules, and their class names have been changed to reflect their new module
locations. The class name changes are as follows:
\table
\header
\li Qt QML
\li Qt Quick
\row
\li
\list
\li QDeclarativeComponent -> QQmlComponent
\li QDeclarativeContext -> QQmlContext
\li QDeclarativeEngine -> QQmlEngine
\li QDeclarativeError -> QQmlError
\li QDeclarativeExpression -> QQmlExpression
\li QDeclarativeExtensionPlugin -> QQmlExtensionPlugin
\li QDeclarativeInfo -> QQmlInfo
\li QDeclarativeListReference -> QQmlListReference
\li QDeclarativeNetworkAccessManagerFactory -> QQmlNetworkAccessManagerFactory
\li QDeclarativeParserStatus -> QQmlParserStatus
\li QDeclarativeProperty -> QQmlProperty
\li QDeclarativePropertyMap -> QQmlPropertyMap
\li QDeclarativePropertyValueSource -> QQmlPropertyValueSource
\li QDeclarativeScriptString -> QQmlScriptString
\endlist
\li
\list
\li QDeclarativeItem -> QQuickItem
\li QDeclarativeView -> QQuickView
\li QDeclarativeImageProvider -> QQuickImageProvider
\endlist
\endtable
To use the new \c QQml* and \c QQuick* classes in Qt 5, link against the approprate module from
your qmake \c .pro file. For example the following will link against both the \l {Qt QML} and \l {Qt Quick}
modules:
\code
QT += qml quick
\endcode
Required header files can then be included:
\code
#include <QtQml/QQmlEngine>
#include <QtQuick/QQuickView>
\endcode
(The \c QtDeclarative module is still available to developers as the \c {Qt Quick 1} module, as
discussed \l {Qt Quick 1}{below}. However, it should not be used for
new applications.)
\section3 QDeclarativeItem and QDeclarativeView
When porting to QQuickItem, note that QDeclarativeItem inherited from QGraphicsItem; in contrast,
QQuickItem inherits directly from QObject, and any QGraphicsItem-specific functionality is no longer
available. In particular, QQuickItem does not have a \c paint() method for performing custom
rendering through the QPainter API. Instead, in Qt 5, custom rendering should be performed through
the new \c QSG* classes to take full advantage of the scene graph. See the \l {Qt Quick Scene Graph}
documentation details on using these classes.
Alternatively, the QQuickPaintedItem provides a \c paint() method and can be used as
a convenient way to port QDeclarativeItem-based classes that use the QPainter API. Note this method
is less performant than using the \c QSG* classes.
When porting from QDeclarativeView to QQuickView, note that QDeclarativeView inherited from
QGraphicsView. In contrast, QQuickView inherits from QQuickWindow and uses the QWindow
infrastructure introduced in Qt 5; any QGraphicsView-specific functionality is no longer available.
\section3 qmlscene Utility
The \c qmlviewer tool provided for prototyping and testing QML applications in Qt 4.x has been
replaced with the \c qmlscene tool which integrates with the new scenegraph features in Qt 5.
\section2 QML plugins
All QML plugins should extend QQmlExtensionPlugin in Qt 5.
Additionally, plugins should use the new Qt plugin infrastructure introduced in Qt 5. QML plugins no
longer require the Q_EXPORT_PLUGIN2() macro. Instead, they should use the Q_PLUGIN_METADATA() macro
within the plugin class declaration.
See the updated \l {qtqml-modules-cppplugins.html}{Creating C++ Plugins For QML} documentation for
an overview of creating QML plugins in Qt 5.
\keyword Qt Quick 1
\section2 QtDeclarative module in Qt 5
For the purposes of porting older applications, the \c {QtDeclarative} module is still available in Qt
5 but has been renamed to \c {Qt Quick 1}. Applications that required Qt Quick 1 specific API (e.g.
QDeclarativeView or QDeclarativeItem and the Graphics View integration) can use this module. Note
that new applications should use the new \l {Qt QML} and \l {Qt Quick} modules instead.
To use the \c {Qt Quick 1} module, add "declarative" to your qmake \c .pro file:
\code
QT += declarative
\endcode
Required header files can be included as follows:
\code
#include <QtDeclarative/QDeclarativeView>
#include <QtDeclarative/QDeclarativeItem>
\endcode
*/
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