// Copyright (C) 2016 The Qt Company Ltd. // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only /*! \example customwidgetplugin \examplecategory {Desktop} \meta tags {widgets,designer} \ingroup examples-designer \title Custom Widget Plugin \brief Creating a custom widget plugin for \QD. \image customwidgetplugin-example.webp In this example, the custom widget used is based on the \l{widgets/analogclock}{Analog Clock example}, and does not provide any custom signals or slots. \section1 Preparation To provide a custom widget that can be used with \QD, we need to supply a self-contained implementation and provide a plugin interface. In this example, we reuse the \l{widgets/analogclock}{Analog Clock example} for convenience. \section1 Project files \section2 CMake The project files need to state that a plugin linking to the \QD libraries is to be built: \snippet customwidgetplugin/CMakeLists.txt 0 \codeline \snippet customwidgetplugin/CMakeLists.txt 2 The link libraries list specifies \c Qt::UiPlugin. This indicates that the plugin uses the abstract interfaces QDesignerCustomWidgetInterface and QDesignerCustomWidgetCollectionInterface only and has no linkage to the \QD libraries. When accessing other interfaces of \QD that have linkage, \c Designer should be used instead; this ensures that the plugin dynamically links to the \QD libraries and has a run-time dependency on them. The following example shows how to add the header and source files of the widget: \snippet customwidgetplugin/CMakeLists.txt 1 We provide an implementation of the plugin interface so that \QD can use the custom widget. It is also important to ensure that the plugin is installed in a location that is searched by \QD. We do this by specifying a target path for the project and adding it to the list of items to install: \snippet customwidgetplugin/CMakeLists.txt 3 \snippet customwidgetplugin/CMakeLists.txt 4 The custom widget is created as a library. It will be installed alongside the other \QD plugins when the project is installed (using \c{ninja install} or an equivalent installation procedure). For more information about plugins, see the \l {How to Create Qt Plugins} documentation. \section2 qmake The following example shows how to link a plugin to the \QD libraries: \snippet customwidgetplugin/customwidgetplugin.pro 0 \codeline \snippet customwidgetplugin/customwidgetplugin.pro 1 The \c QT variable contains the keyword \c uiplugin, which is the equivalent of the \c Qt::UiPlugin library. The following example shows how to add the header and source files of the widget: \snippet customwidgetplugin/customwidgetplugin.pro 2 The following example shows how to install a plugin to the \QD's plugin path: \snippet customwidgetplugin/customwidgetplugin.pro 3 \section1 AnalogClock Class Definition and Implementation The \c AnalogClock class is defined and implemented in exactly the same way as described in the \l{widgets/analogclock}{Analog Clock example}. Since the class is self-contained, and does not require any external configuration, it can be used without modification as a custom widget in \QD. \section1 AnalogClockPlugin Class Definition The \c AnalogClock class is exposed to \QD through the \c AnalogClockPlugin class. This class inherits from both QObject and the QDesignerCustomWidgetInterface class, and implements an interface defined by QDesignerCustomWidgetInterface. To ensure that Qt recognizes the widget as a plugin, export relevant information about the widget by adding the \c Q_PLUGIN_METADATA() macro: \snippet customwidgetplugin/customwidgetplugin.h 0 The functions provide information about the widget that \QD can use in the \l{Getting to Know Qt Widgets Designer#WidgetBox}{widget box}. The \c initialized private member variable is used to record whether the plugin has been initialized by \QD. Note that the only part of the class definition that is specific to this particular custom widget is the class name. \section1 AnalogClockPlugin Implementation The class constructor simply calls the QObject base class constructor and sets the \c initialized variable to \c false. \snippet customwidgetplugin/customwidgetplugin.cpp 0 \QD will initialize the plugin when it is required by calling the \c initialize() function: \snippet customwidgetplugin/customwidgetplugin.cpp 1 In this example, the \c initialized private variable is tested, and only set to \c true if the plugin is not already initialized. Although, this plugin does not require any special code to be executed when it is initialized, we could include such code after the test for initialization. The \c isInitialized() function lets \QD know whether the plugin is ready for use: \snippet customwidgetplugin/customwidgetplugin.cpp 2 Instances of the custom widget are supplied by the \c createWidget() function. The implementation for the analog clock is straightforward: \snippet customwidgetplugin/customwidgetplugin.cpp 3 In this case, the custom widget only requires a \c parent to be specified. If other arguments need to be supplied to the widget, they can be introduced here. The following functions provide information for \QD to use to represent the widget in the widget box. The \c name() function returns the name of class that provides the custom widget: \snippet customwidgetplugin/customwidgetplugin.cpp 4 The \c group() function is used to describe the type of widget that the custom widget belongs to: \snippet customwidgetplugin/customwidgetplugin.cpp 5 The widget plugin will be placed in a section identified by its group name in \QD's widget box. The icon used to represent the widget in the widget box is returned by the \c icon() function: \snippet customwidgetplugin/customwidgetplugin.cpp 6 In this case, we return a null icon to indicate that we have no icon that can be used to represent the widget. A tool tip and "What's This?" help can be supplied for the custom widget's entry in the widget box. The \c toolTip() function should return a short message describing the widget: \snippet customwidgetplugin/customwidgetplugin.cpp 7 The \c whatsThis() function can return a longer description: \snippet customwidgetplugin/customwidgetplugin.cpp 8 The \c isContainer() function tells \QD whether the widget is supposed to be used as a container for other widgets. If not, \QD will not allow the user to place widgets inside it. \snippet customwidgetplugin/customwidgetplugin.cpp 9 Most widgets in Qt can contain child widgets, but it only makes sense to use dedicated container widgets for this purpose in \QD. By returning \c false, we indicate that the custom widget cannot hold other widgets; if we returned true, \QD would allow other widgets to be placed inside the analog clock and a layout to be defined. The \c domXml() function provides a way to include default settings for the widget in the standard XML format used by \QD. In this case, we only specify the widget's geometry: \snippet customwidgetplugin/customwidgetplugin.cpp 10 If the widget provides a reasonable size hint, it is not necessary to define it here. In addition, returning an empty string instead of a \c{} element will tell \QD not to install the widget in the widget box. To make the analog clock widget usable by applications, we implement the \c includeFile() function to return the name of the header file containing the custom widget class definition: \snippet customwidgetplugin/customwidgetplugin.cpp 12 */