Container Extension Example▲

The Container Extension example shows how to create a custom multi-page plugin for Qt Designer using the QDesignerContainerExtension class.

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To provide a custom widget that can be used with Qt Designer, we need to supply a self-contained implementation. In this example we use a custom multi-page widget designed to show the container extension feature.

An extension is an object which modifies the behavior of Qt Designer. The QDesignerContainerExtension enables Qt Designer to manage and manipulate a custom multi-page widget, i.e. adding and deleting pages to the widget.

There are four available types of extensions in Qt Designer:

  • QDesignerMemberSheetExtension provides an extension that allows you to manipulate a widget's member functions which is displayed when configuring connections using Qt Designer's mode for editing signals and slots.

  • QDesignerPropertySheetExtension provides an extension that allows you to manipulate a widget's properties which is displayed in Qt Designer's property editor.

  • QDesignerTaskMenuExtension provides an extension that allows you to add custom menu entries to Qt Designer's task menu.

  • QDesignerContainerExtension provides an extension that allows you to add (and delete) pages to a multi-page container plugin in Qt Designer.

You can use all the extensions following the same pattern as in this example, only replacing the respective extension base class. For more information, see Qt Designer C++ Classes.

The Container Extension example consists of four classes:

  • MultiPageWidget is a custom container widget that lets the user manipulate and populate its pages, and navigate among these using a combobox.

  • MultiPageWidgetPlugin exposes the MultiPageWidget class to Qt Designer.

  • MultiPageWidgetExtensionFactory creates a MultiPageWidgetContainerExtension object.

  • MultiPageWidgetContainerExtension provides the container extension.

The project file for custom widget plugins needs some additional information to ensure that they will work within Qt Designer. For example, custom widget plugins rely on components supplied with Qt Designer, and this must be specified in the project file that we use. We will first take a look at the plugin's project file.

Then we will continue by reviewing the MultiPageWidgetPlugin class, and take a look at the MultiPageWidgetExtensionFactory and MultiPageWidgetContainerExtension classes. Finally, we will take a quick look at the MultiPageWidget class definition.

The Project File: containerextension.pro▲

The project file must contain some additional information to ensure that the plugin will work as expected:

 
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TEMPLATE = lib
CONFIG  += plugin
QT      += widgets designer

The TEMPLATE variable's value makes qmake create the custom widget as a library. Later, we will ensure that the widget will be recognized as a plugin by Qt by using the Q_PLUGIN_METADATA() macro to export the relevant widget information.

The CONFIG variable is set to plugin, which ensures that qmake considers the custom widget a plugin library.

The QT variable contains the value designer. Since the plugin uses components supplied with Qt Designer that require linkage, this value ensures that our plugin links against Qt Designer's library (libQtDesigner.so).

The header and source files for the widget are declared in the usual way:

 
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HEADERS += multipagewidget.h \
           multipagewidgetplugin.h \
           multipagewidgetcontainerextension.h \
           multipagewidgetextensionfactory.h

SOURCES += multipagewidget.cpp \
           multipagewidgetplugin.cpp \
           multipagewidgetcontainerextension.cpp \
           multipagewidgetextensionfactory.cpp

OTHER_FILES += multipagewidget.json

We provide an implementation of the plugin interface so that Qt Designer can use the custom widget. In this particular example we also provide implementations of the container extension interface and the extension factory.

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:

 
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