How to use a Enum as QProperty and update it using a stylesheet?

How to use an Enum as QProperty and update its value using a stylesheet?

class Gallery : public QScrollArea
{
    Q_OBJECT
    Q_PROPERTY(int horizontalSpacing MEMBER horizontalSpacing) 
    Q_PROPERTY(Orientation orientation MEMBER orientation WRITE setOrientation)

public:
    int horizontalSpacing;

    enum Orientation { TOP, BOTTOM, LEFT, RIGHT };
    Orientation orientation;
    void setOrientation(Orientation orientation);
};

Using:

Gallery
{
    qproperty-horizontalSpacing: 30;
    qproperty-orientation: "left";
}

the setOrientation function is not called.
Using:

Gallery
{
    qproperty-horizontalSpacing: 30;
    qproperty-orientation: left;
}

The function is called but, the value of orientation is 19, what does this mean?

void Gallery::setOrientation(Orientation orientation)
{
}

It seems using MEMBER with one accessor (WRITE in this case) to handle a custom property, causes undefined behavior that is noticed when fetching the int value of Orientation enum.

To work around that, here are 2 solutions, and both require adding Q_ENUM(someEnum):

Solution 1:

Use only READ and WRITE to set orientation:

class Gallery : public QScrollArea
{
    Q_OBJECT
    Q_PROPERTY(Orientation orientation READ getOrientation WRITE setOrientation)

public:
    enum Orientation { TOP, BOTTOM, LEFT, RIGHT };
    Orientation orientation;
    Q_ENUM(Orientation)

    void setOrientation(Orientation orient)
    {
        orientation = orient;
    }
    Orientation getOrientation()
    {
        return orientation;
    }
};

When setting stylesheet, quotes are mandatory, as well as matching the casing, which is all uppercase in this case:

Gallery
{
    qproperty-orientation: "LEFT";
}

Solution 2:

Use MEMBER on its own:

class Gallery : public QWidget
{
    Q_OBJECT
    Q_PROPERTY(Orientation orientation MEMBER orientation)

public:
    enum Orientation { TOP, BOTTOM, LEFT, RIGHT };
    Orientation orientation;
    Q_ENUM(Orientation)
};

Same rules for the stylesheet.

I'll include this explanation from this answer on Q_PROPERTY: MEMBER vs READ/WRITE:

>...you can either use MEMBER and rely on auto generated, trivial accessor functions or define for yourself those functions if they happen to be more complex than a defaulted one.

For more:

• Qt Documentation: The Property System