How to use flags as custom widget property type in QT?

Question

I have trouble to use flags as QT custom widget property type. The expected property does not show on QT Designer property editor.

The code is as below:

#ifndef SVBASICDEMO_H
#define SVBASICDEMO_H

#include <QString>
#include <QtUiPlugin/QDesignerExportWidget>
#include <QWidget>
#include <QLabel>
#include "svbasicwidget.h"

QT_BEGIN_NAMESPACE

namespace Company {
namespace Product {
namespace Widget {
namespace Basic {
class QDESIGNER_WIDGET_EXPORT SvBasicDemo : public SvBasicWidget
{
    Q_OBJECT
        Q_FLAGS(SvBasicDemo::AccessTypes)
        Q_PROPERTY(QString url_prop MEMBER url_prop NOTIFY propertyChange)
        Q_PROPERTY(Priority enum_prop MEMBER enum_prop NOTIFY propertyChange)
        Q_PROPERTY(AccessTypes flag_prop MEMBER flag_prop NOTIFY propertyChange)
        Q_PROPERTY(Qt::Alignment flag_prop_2 MEMBER flag_prop_2 NOTIFY propertyChange)

    Q_SIGNALS:
    void propertyChange();

    public slots:
    //更新属性的槽
    void updateProperty();

public:
    SvBasicDemo(QWidget *parent = 0);
    virtual void refresh_binding_cb();
    virtual QString help_info() const;

    enum Priority { High, Low, VeryHigh, VeryLow };
    Q_ENUM(Priority)

    enum AccessType { Read = 0x1, Write = 0x2 };

    Q_DECLARE_FLAGS(AccessTypes, AccessType)

private:
    QString url_prop;
    Priority enum_prop;
    AccessTypes flag_prop;
    Qt::Alignment flag_prop_2;
    QLabel label;
};

Q_DECLARE_OPERATORS_FOR_FLAGS(SvBasicDemo::AccessTypes)

}
}
}
}

QT_END_NAMESPACE
#endif

The result in qt designer property editor is shown as below:

You can see property enum_prop (use custom enum) and flag_prop_2 (use built in flag Qt::Alignment) works as expected. But property flag_prop is missing.

I have study the code in "%QT_ROOT%\Qt5.6.0\5.6\msvc2013\include\QtWidgets\qgraphicsview.h"。 And did not figure out why.

Could anyone give me some hint about why it does not work as expected? Thanks in advance.

Answer 1

After tried many times, finally solved this issue. The key point is:

1. It seems MEMBER keyword does not work with Q_FLAGS property;

2. Q_DECLARE_OPERATORS_FOR_FLAGS macro must used in global namespace;

   namespace Company {
   
       namespace Product {
       namespace Widget {
       namespace Basic {
       class QDESIGNER_WIDGET_EXPORT SvBasicDemo : public SvBasicWidget
       {
           Q_OBJECT
               Q_FLAGS(AccessTypes)
               Q_PROPERTY(QString url_prop MEMBER url_prop NOTIFY propertyChange)
               Q_PROPERTY(Priority enum_prop MEMBER enum_prop NOTIFY propertyChange)
               // Q_PROPERTY(AccessTypes flag_prop MEMBER flag_prop NOTIFY propertyChange) // Cannot use MEMBER here, otherwise, the property will not show on qt designer property editor. I don't know why.
               Q_PROPERTY(AccessTypes flag_prop READ getAccessTypes WRITE setAccessTypes)
               Q_PROPERTY(Qt::Alignment flag_prop_3 MEMBER flag_prop_2 NOTIFY propertyChange)
   
       Q_SIGNALS:
       void propertyChange();
   
       public slots:
       void updateProperty();
   
   public:
       SvBasicDemo(QWidget *parent = 0);
       virtual void refresh_binding_cb();
       virtual QString help_info() const;
   
       enum Priority { High, Low, VeryHigh, VeryLow };
       Q_ENUM(Priority)
   
       enum AccessType { None = 0x0, Read = 0x1, Write = 0x2 };
       Q_DECLARE_FLAGS(AccessTypes, AccessType)
   
       inline AccessTypes getAccessTypes() const
       {
           return flag_prop;
       }
       inline void setAccessTypes(AccessTypes features)
       {
           flag_prop = features;
       }
   
   private:
       QString url_prop;
       Priority enum_prop;
       AccessTypes flag_prop;
       Qt::Alignment flag_prop_2;
       QLabel label;
   };
   }
   }
   }
   }
   // must use this macro outside namespace
   Q_DECLARE_OPERATORS_FOR_FLAGS(Company::Product::Widget::Basic::SvBasicDemo::AccessTypes)
   

Answer 2

Have you add the Q_DECLARE_FLAGS macro? See also the correct usage of Q_FLAGS()

This is an example of the WindowsStateFlags definition:

class MyClass
{
public:
    enum Option {
        NoOptions = 0x0,
        ShowTabs = 0x1,
        ShowAll = 0x2,
        SqueezeBlank = 0x4
    };
    Q_DECLARE_FLAGS(Options, Option)
    Q_FLAGS(Options)
    ...
};

Q_DECLARE_OPERATORS_FOR_FLAGS(MyClass::Option)

You have to add the property macro and the invocable function to get the curren option:

Q_PROPERTY(Option option READ getOption())
Q_INVOKABLE Option getOption() const;

And register the metatype qRegisterMetaType or Q_DECLARE_METATYPE():

Q_DECLARE_METATYPE(MyClass::Option);