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Thread: Memory management of QAction

  1. #1
    Join Date
    Jul 2016
    Qt products
    Unix/X11 Windows

    Default Memory management of QAction


    I have a question with the following piece of code that can be found here

    Qt Code:
    1. QMenu *MainWindow::createColorMenu(const char *slot, QColor defaultColor)
    2. {
    3. QList<QColor> colors;
    4. colors << Qt::black << Qt::white << Qt::red << Qt::blue << Qt::yellow;
    5. QStringList names;
    6. names << tr("black") << tr("white") << tr("red") << tr("blue")
    7. << tr("yellow");
    9. QMenu *colorMenu = new QMenu(this);
    10. for (int i = 0; i < colors.count(); ++i) {
    11. QAction *action = new QAction(, this);
    12. action->setData(;
    13. action->setIcon(createColorIcon(;
    14. connect(action, SIGNAL(triggered()), this, slot);
    15. colorMenu->addAction(action);
    16. if ( == defaultColor)
    17. colorMenu->setDefaultAction(action);
    18. }
    19. return colorMenu;
    20. }
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    According to the doc of QWidget::addAction(QAction *action), the ownership of action is not transferred to the QWidget, so I wonder if the memory of each action created are correctly released.

    Thank you

  2. #2
    Join Date
    Jan 2008
    Alameda, CA, USA
    Thanked 773 Times in 763 Posts
    Qt products
    Windows Android

    Default Re: Memory management of QAction

    I wonder if the memory of each action created are correctly released.
    You create your QAction instances using "this" as the parent object instance. So when your MainWindow goes out of scope (presumably when your program exits, if you create it in main() as is the usual case), these instances will be deleted since they are children of MainWindow.

    If you create them without a parent (eg. "new QAction( "Some text" );") then they will not be deleted until the runtime cleans up dangling memory when your program exits.

    The reason why QAction ownership is not transferred to the widget when setting them on it is because QActions are designed to be shared - the same QAction instance can be assigned to a menu, toolbar, or anything else that can accept actions. This wouldn't be possible if there was a strict ownership hierarchy based on the widget to which the action was assigned.
    <=== The Great Pumpkin says ===>
    Please use CODE tags when posting source code so it is more readable. Click "Go Advanced" and then the "#" icon to insert the tags. Paste your code between them.

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