Change ownership for value type property

squareroot13

According to Qt documentation:
"""
Data Ownership

When data is transferred from C++ to QML, the ownership of the data always remains with C++. The exception to this rule is when a QObject is returned from an explicit C++ method call: in this case, the QML engine assumes ownership of the object, unless the ownership of the object has explicitly been set to remain with C++ by invoking QQmlEngine::setObjectOwnership() with QQmlEngine::CppOwnership specified.
"""
It means that returned object from call of getter function of properties doesn't change a ownership.
When i have some, derived from QObject class with properties of simple type(int, QString...), registered in QML (via qmlRegisterSingletonType) and used as CppOwnership instance.

class TCustomDraw: public QObject
   {
       Q_OBJECT
   public:
       Q_PROPERTY (QColor color READ colorValue NOTIFY colorChanged)
       QColor colorValue() const
       {
           return m_color;
       }
   signals:
       void colorChanged();
   private:
       QColor m_color;
   };

And QML main window:

import QtQuick 2.12
    import QtQuick.Controls 2.12
    import QtQuick.Controls 1.4
    import QtQuick.Controls.Styles  1.4
    import QtQuick.Dialogs 1.1
    import QtQuick.Layouts 1.0
    ]import QtQuick.Window 2.12
    import Qt.labs.platform 1.1
    import QtQml 2.12
    import QtQuick.Shapes 1.12
    import customdraw 1.0
     
    Window {
        id: wnd
        width: 640
        height: 480
        visible: true
        Button {
            anchors.fill: parent
            onClicked: {
                 var f = TCustomDraw.color 
            }
        }
    }

What happens with ownership of color object when i press the Button ?
If ownership of color object remains in c++ does it mean a memory leakage ?

SGaist

Hi,

It's the QObject ownership that is concerned not the value type it handles.

squareroot13

@SGaist said in Change ownership for value type property:

Hi,

It's the QObject ownership that is concerned not the value type it handles.

I think the same, but meaning of qt documentation at this place is ambiguous.