QDesignerCustomWidgetCollectionInterface Class

Detailed Description

When implementing a custom widget plugin, you build it as a separate library. If you want to include several custom widget plugins in the same library, you must in addition subclass QDesignerCustomWidgetCollectionInterface.

QDesignerCustomWidgetCollectionInterface contains one single function returning a list of the collection's QDesignerCustomWidgetInterface objects. For example, if you have several custom widgets CustomWidgetOne, CustomWidgetTwo and CustomWidgetThree, the class definition may look like this:

 #include customwidgetoneinterface.h
 #include customwidgettwointerface.h
 #include customwidgetthreeinterface.h

 #include <QtDesigner/qtdesigner.h>
 #include <QtCore/qplugin.h>

 class MyCustomWidgets: public QObject, public QDesignerCustomWidgetCollectionInterface
 {
     Q_OBJECT
     Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QDesignerCustomWidgetCollectionInterface")
     Q_INTERFACES(QDesignerCustomWidgetCollectionInterface)

 public:
     MyCustomWidgets(QObject *parent = 0);

     QList<QDesignerCustomWidgetInterface*> customWidgets() const override;

 private:
     QList<QDesignerCustomWidgetInterface*> widgets;
 };

In the class constructor you add the interfaces to your custom widgets to the list which you return in the customWidgets() function:

 MyCustomWidgets::MyCustomWidgets(QObject *parent)
         : QObject(parent)
 {
     widgets.append(new CustomWidgetOneInterface(this));
     widgets.append(new CustomWidgetTwoInterface(this));
     widgets.append(new CustomWidgetThreeInterface(this));
 }

 QList<QDesignerCustomWidgetInterface*> MyCustomWidgets::customWidgets() const
 {
     return widgets;
 }

Note that instead of exporting each custom widget plugin using the Q_PLUGIN_METADATA() macro, you export the entire collection. The Q_PLUGIN_METADATA() macro ensures that Qt Designer can access and construct the custom widgets. Without this macro, there is no way for Qt Designer to use them.