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.

Might be that you have to expose the underlying enum to the meta object model. Try adding `Q_ENUM(AccessType)` — king_nak, Feb 20 '17 at 10:02

score 1 · Accepted Answer · edited May 14 '19 at 11:42

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

It seems MEMBER keyword does not work with Q_FLAGS property;

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)

score 0 · Answer 2 · answered Feb 20 '17 at 15:48

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);

Thanks very much for your reply. As attached in my original post, I use these macro following the code in qgraphicsview.h as below: ````Q_FLAGS(SvBasicDemo::AccessTypes) Q_DECLARE_FLAGS(AccessTypes, AccessType) Q_DECLARE_OPERATORS_FOR_FLAGS(SvBasicDemo::AccessTypes)```` Is there something wrong in my code? Is there something to do with the namespace? — ricky, Feb 21 '17 at 06:01

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

2 Answers2