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.
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:
The QtQuick module has been updated to version 2. All QML applications should update their import statements to use the new version:
import QtQuick 2.3
highlightMoveSpeed
and
highlightResizeSpeed
properties have been renamed to
highlightMoveVelocity
and
highlightResizeVelocity
，分别。
openSoftwareInputPanel()
and
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.
QtQuick.LocalStorage
singleton type. Any code that requires the local storage API must import
QtQuick
.LocalStorage
instead. See the
Qt Quick Local Storage
documentation for examples.
LayoutItem
type has been removed from the
QtQuick
module as it was specific to the Graphics View framework backend used in
Qt Quick 1
.
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:
(visible && opacity > 0.0)
.
opacity
changed to 0, or its
visible
value became
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
visible
is
false
; the item opacity no longer affects whether the item is laid out. (This is consistent with the existing behavior of
ListView
and
GridView
).
文本：
PlainText
而不是
AutoText
.
Text.AutoText
format, the text object will automatically switch to
Text.StyledText
而不是
Text.RichText
.
其它：
cacheBuffer
property now has a non-zero default and delegates in the cache buffer are created asynchronously. Also, using a
RightToLeft
layout now also reverses the
preferredHighlightBegin
and
preferredHighlightEnd
.
sourceChanged
and
sourceComponentChanged
signals are now only emitted when their respective properties change value. (Previously
Loader
emitted both of these signals when either of the relevant properties had changed.)
Qt.labs.particles
module has been removed. It is replaced by the fully-fledged
QtQuick.Particles
module which is an enormous improvement on its predecessor.
Qt.labs.shaders
module has been removed as the
ShaderEffectItem
and
ShaderEffectSource
types from this module have been moved into the
QtQuick
module. Note the
ShaderEffectItem
type has been renamed to
ShaderEffect
.
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
QtDeclarative
module has been deprecated in favor of two new modules:
Qt QML
, which implements the QML engine and language infrastructure, and
Qt Quick
, which implements the visual canvas and scenegraph backend.
All classes that were previously in the
QtDeclarative
module have been moved into the
Qt QML
and
Qt Quick
modules, and their class names have been changed to reflect their new module locations. The class name changes are as follows:
| Qt QML | Qt Quick |
|---|---|
|
|
To use the new
QQml*
and
QQuick*
classes in Qt 5, link against the approprate module from your qmake
.pro
file. For example the following will link against both the
Qt QML
and
Qt Quick
模块：
QT += qml quick
Required header files can then be included:
#include <QtQml/QQmlEngine> #include <QtQuick/QQuickView>
(
QtDeclarative
模块对开发者仍然可用因为
Qt Quick 1
模块，如论述
below
。不管怎样，不应该将它用于新应用程序)。
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
paint()
method for performing custom rendering through the
QPainter
API. Instead, in Qt 5, custom rendering should be performed through the new
QSG*
classes to take full advantage of the scene graph. See the
Qt Quick 场景图形
documentation details on using these classes.
另外，
QQuickPaintedItem
提供
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
QSG*
类。
When porting from QDeclarativeView to QQuickView , note that QDeclarativeView inherited from QGraphicsView . In contrast, QQuickView 继承自 QQuickWindow and uses the QWindow infrastructure introduced in Qt 5; any QGraphicsView -specific functionality is no longer available.
The
qmlviewer
tool provided for prototyping and testing QML applications in Qt 4.x has been replaced with the
qmlscene
tool which integrates with the new scenegraph features in Qt 5.
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 为 QML 创建 C++ 插件 documentation for an overview of creating QML plugins in Qt 5.
For the purposes of porting older applications, the
QtDeclarative
module is still available in Qt 5 but has been renamed to
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
Qt QML
and
Qt Quick
modules instead.
要使用
Qt Quick 1
模块，添加 declrative 到 qmake
.pro
文件：
QT += declarative
Required header files can be included as follows:
#include <QtDeclarative/QDeclarativeView> #include <QtDeclarative/QDeclarativeItem>