Exposing your plugin to Qt Designer

The FilterWidget class is completed and ready to be used. We now have to register FilterWidget with the Qt Designer plugin system. This glue code is made using a child class of QDesignerCustomWidgetInterface.

Create a new C++ class named FilterPluginDesigner and update FilterPluginDesigner.h like so:

#include <QtUiPlugin/QDesignerCustomWidgetInterface> 
 
class  FilterPluginDesigner : public QObject, public QDesignerCustomWidgetInterface 
{ 
    Q_OBJECT 
    Q_PLUGIN_METADATA(IID 
        "org.masteringqt.imagefilter.FilterWidgetPluginInterface") 
    Q_INTERFACES(QDesignerCustomWidgetInterface) 
public: 
FilterPluginDesigner(QObject* parent = 0); 
}; 

The FilterPlugin class inherits from two classes:

• The QObject class, to rely on the Qt parenting system

• The QDesignerCustomWidgetInterface class to properly expose the FilterWidget information to the plugin system

The QDesignerCustomWidgetInterface class brings two new macros:

• The Q_PLUGIN_METADATA() macro...