[Development] QAction in Qt 6 - next step proposal

[Olivier Goffart]

On 27.11.19 11:19, Friedemann Kleint wrote:
> Hi,
> 
> as discussed on the change, there is not much one can do with the newly
> introduced QGuiAction; it serves as a base class for QAction and
> QQuickAction, The naming follows the Q(Gui)Application pattern.
> 
>   > QMenu *menu() const;
>   > -> static QMenu *QMenu::menuForAction(QAction *action);
> 
>   > void setMenu(QMenu *menu);
>   > -> static void QMenu::setMenuForAction(QAction *action, QMenu *menu);
> 
> This  in my opinion is a no-go, we cannot do source-incompatible changes
> in this area because there have been many deprecations already and code
> needs to compile against 5 and 6 with minimal changes.
> 
> Ofc, having one QAction class in QtGui is desirable; but it must not
> infer source-incompatible changes (and no, hacks like forward declaring
> QWidget from QtGui or similar are also a no-go since it causes trouble
> for Qt for Python).

You can keep the API as is in QAction in QtGui, and have the implementation in 
QtWidgets:


in QtGui/qaction.h

// forward declare classes from QtWidget
class QMenu;
class QWidget;

class Q_GUI_EXPORT  QAction {
   // ...

   // that's ok, the class is forward declared
   void setMenu(QMenu *);
   QMenu *menu() const;

}


// in QtGui/private/qaction_p.h

class Q_GUI_EXPORT QActionHooks {
public:

    virtual void setMenu(QAction *, QMenu *) = 0;
    virtual QMenu *menu(const QAction *) = 0;
    // ...

    static QActionWidgetsHooks *instance;
};

// in QtGui/qaction.cpp

void QAction::setMenu(QMenu *menu) {
     if (!QActionHooks::instance) {
         qWarning("QAction::setMenu: can only be used in a QApplication") ;
         return;
     }
     QActionHooks::instance->setMenu(this, menu);
}

// in QtWidgets/qapplication.cpp

#include <QtWidgets/private/qwidgetsactionhook_p.h> // implements QActionHooks

void QApplication::QApplication(...) {
    // ...
    static const QWidgetActionHooks actionHooks;
    QActionWidgetsHooks::instance = &actionHooks;
    // ...
}




That's just an example, there is other ways to do it.