Creating a custom widget plugin for Qt Designer that uses signals and slots.
In this example, we simply extend the 自定义 Widget 插件 example and its custom widget (based on the 指针式时钟 example), by introducing the concept of signals and slots.
The World Time Clock Plugin example consists of two classes:
WorldTimeClock
is a custom clock widget with hour and minute hands that is automatically updated every few seconds.
WorldTimeClockPlugin
exposes the
WorldTimeClock
class to
Qt Designer
.
First we will take a look at the
WorldTimeClock
class which extends the
自定义 Widget 插件
example's
AnalogClock
class by providing a signal and a slot. Then we will take a quick look at the
WorldTimeClockPlugin
class, but this class is in most parts identical to the
自定义 Widget 插件
example's implementation.
Finally we take a look at the plugin's project file. The project file for custom widget plugins needs some additional information to ensure that they will work within Qt Designer . This is also covered in the 自定义 Widget 插件 example, but due to its importance (custom widget plugins rely on components supplied with Qt Designer which must be specified in the project file that we use) we will repeat it here.
The
WorldTimeClock
类继承
QWidget
, and is a custom clock widget with hour and minute hands that is automatically updated every few seconds. What makes this example different from the
自定义 Widget 插件
example, is the introduction of the signal and slot in the custom widget class:
class QDESIGNER_WIDGET_EXPORT WorldTimeClock : public QWidget { Q_OBJECT public: explicit WorldTimeClock(QWidget *parent = nullptr); public slots: void setTimeZone(int hourOffset); signals: void updated(QTime currentTime); protected: void paintEvent(QPaintEvent *event) override; private: int timeZoneOffset = 0; };
Note the use of the QDESIGNER_WIDGET_EXPORT macro. This is needed to ensure that Qt Designer can create instances of the widget on some platforms, but it is a good idea to use it on all platforms.
We declare the
setTimeZone()
slot with an associated
timeZoneOffset
variable, and we declare an
updated()
signal which takes the current time as argument and is emitted whenever the widget is repainted.
在
Qt Designer
's workspace we can then, for example, connect the
WorldTimeClock
小部件的
updated()
signal to a
QTimeEdit
's
setTime()
slot using
Qt Designer
's mode for editing signal and slots.
We can also connect a
QSpinBox
's
valueChanged()
信号到
WorldTimeClock
's
setTimeZone()
槽。
The
WorldTimeClockPlugin
class exposes the
WorldTimeClock
class to
Qt Designer
. Its definition is equivalent to the
自定义 Widget 插件
example's plugin class which is explained in detail. The only part of the class definition that is specific to this particular custom widget is the class name:
class WorldTimeClockPlugin : public QObject, public QDesignerCustomWidgetInterface { Q_OBJECT Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QDesignerCustomWidgetInterface") Q_INTERFACES(QDesignerCustomWidgetInterface) public: explicit WorldTimeClockPlugin(QObject *parent = nullptr); bool isContainer() const override; bool isInitialized() const override; QIcon icon() const override; QString domXml() const override; QString group() const override; QString includeFile() const override; QString name() const override; QString toolTip() const override; QString whatsThis() const override; QWidget *createWidget(QWidget *parent) override; void initialize(QDesignerFormEditorInterface *core) override; private: bool initialized = false; };
The plugin class provides
Qt Designer
with basic information about our plugin, such as its class name and its include file. Furthermore it knows how to create instances of the
WorldTimeClockPlugin
小部件。
WorldTimeClockPlugin
also defines the
initialize()
function which is called after the plugin is loaded into
Qt Designer
. The function's
QDesignerFormEditorInterface
parameter provides the plugin with a gateway to all of
Qt Designer
's API's.
The
WorldTimeClockPlugin
class inherits from both
QObject
and
QDesignerCustomWidgetInterface
. It is important to remember, when using multiple inheritance, to ensure that all the interfaces (i.e. the classes that doesn't inherit
Q_OBJECT
) are made known to the meta object system using the
Q_INTERFACES
() macro. This enables
Qt Designer
要使用
qobject_cast
(QObject * object) to query for supported interfaces using nothing but a
QObject
指针。
实现为
WorldTimeClockPlugin
is also equivalent to the plugin interface implementation in the
自定义 Widget 插件
example (only the class name and the implementation of
QDesignerCustomWidgetInterface::domXml
() differ). The main thing to remember is to use the
Q_PLUGIN_METADATA
() macro to export the
WorldTimeClockPlugin
class for use with
Qt Designer
:
Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QDesignerCustomWidgetInterface")
Without this macro, there is no way for Qt Designer to use the widget.
The project file for custom widget plugins needs some additional information to ensure that they will work as expected within Qt Designer :
QT += widgets uiplugin CONFIG += plugin TEMPLATE = lib
The
TEMPLATE
variable's value in conjunction with the keyword
plugin
在
CONFIG
variable make
qmake
create the custom widget as a plugin library.
The
QT
variable contains the keyword
uiplugin
. This plugin type provides a factory function for custom widget creation by implementing the abstract interfaces
QDesignerCustomWidgetInterface
or
QDesignerCustomWidgetCollectionInterface
, suitable for use with
QUiLoader
. It does not have a dependency on the
Qt Designer
libraries. Plugins accessing other interfaces of
Qt Designer
to implement container extensions or other
Qt Designer
specific functionality follow different rules and are covered by other examples.
The header and source files for the widget are declared in the usual way, and in addition we provide an implementation of the plugin interface so that Qt Designer can use the custom widget.
HEADERS = worldtimeclock.h \ worldtimeclockplugin.h SOURCES = worldtimeclock.cpp \ worldtimeclockplugin.cpp
It is important to ensure that the plugin is installed in a location that is searched by Qt Designer . We do this by specifying a target path for the project and adding it to the list of items to install:
target.path = $$[QT_INSTALL_PLUGINS]/designer INSTALLS += target
The custom widget is created as a library, and will be installed alongside the other
Qt Designer
plugins when the project is installed (using
make install
or an equivalent installation procedure). Later, we will ensure that it is recognized as a plugin by
Qt Designer
by using the
Q_PLUGIN_METADATA
() macro to export the relevant widget information.
Note that if you want the plugins to appear in a Visual Studio integration, the plugins must be built in release mode and their libraries must be copied into the plugin directory in the install path of the integration (for an example, see
C:/program files/trolltech as/visual studio integration/plugins
).
For more information about plugins, see the 如何创建 Qt 插件 文档。