containerextension.pro Example File
containerextension/containerextension.pro
 QTDIR_build {
 # This is only for the Qt build. Do not use externally. We mean it.
 PLUGIN_TYPE = designer
 PLUGIN_CLASS_NAME = MultiPageWidgetPlugin
 load(qt_plugin)
 CONFIG += install_ok
 } else {
 # Public example:
 TEMPLATE = lib
 CONFIG  += plugin
 TARGET   = $$qtLibraryTarget($$TARGET)
 target.path = $$[QT_INSTALL_PLUGINS]/designer
 INSTALLS += target
 }
 QT      += widgets designer
 HEADERS += multipagewidget.h \
            multipagewidgetplugin.h \
            multipagewidgetcontainerextension.h \
            multipagewidgetextensionfactory.h
 SOURCES += multipagewidget.cpp \
            multipagewidgetplugin.cpp \
            multipagewidgetcontainerextension.cpp \
            multipagewidgetextensionfactory.cpp
 OTHER_FILES += multipagewidget.json