自定义类型的Qml属性

Question

I have a class defined as follows:

class Set : public QObject {
    Q_OBJECT
    …
};

It's qmRegisterType'd and so is usable within QML. I'd like to have in that class property of custom type SetRange, which is defined as follows:

class SetRange : public QObject {
public:
    SetRange ( QObject *parent = 0 ) : QObject::QObject(parent) { }
    Q_PROPERTY(int lowerBound MEMBER lower_bound WRITE setLowerBound NOTIFY lowerBoundChanged)
    Q_PROPERTY(int length MEMBER length WRITE setLength NOTIFY lengthChanged)
    int lower_bound, length;
    void setLowerBound ( int lower_bound ) {
        if ( lower_bound != this->lower_bound )
            emit lowerBoundChanged(this->lower_bound = lower_bound);
    }
    void setLength ( int length ) {
        if ( length != this->length )
            emit lengthChanged(this->length = length);
    }
signals:
    void lowerBoundChanged ( int lower_bound );
    void lengthChanged ( int length );
};
Q_DECLARE_METATYPE(SetRange)

And the property within Set:

Q_PROPERTY(SetRange range READ range WRITE setRange NOTIFY rangeChanged)
void setRange ( SetRange const &range );
SetRange range ( ) const;

I expect to use it in QML as follows:

Set {
    …
    range: Range {
        lowerBound: …
        length: …
    }
}

Currently I have compile-time errors: use of deleted function: SetRange::SetRange(SetRange&&) What should be a proper way to declare custom type to be able to use property of this type both in C++ class and in QML? This type is qmlRegisterType'd too.

Update: Works well even without Q_DECLARE_METATYPE if property range is declared as SetRange* (pointer to SetRange) and other code is modified accordingly. So the should QML property of custom type always be a pointer to this type?

Answer 1

If your custom property type SetRange is derived from QObject which is not copyable as pointed out in comment by @Vercetti, then your property range can not use SetRange as its type because function setRange() will not work.

One solution is to use a pointer to SetRange as type for your property range , as you have already suggested:

Q_PROPERTY(SetRange * range READ range WRITE setRange NOTIFY rangeChanged)

I have been using this solution in all of my custom property types which are derived from QObject. This always works, and is like a standard coding pattern for me.