How to iterate through a menu's actions in Qt?

Question

I'm working in a project where I need to open (show or popup) automatically the items in the QMenuBar.

Let's say I have the next menu bar:

 File     Edit      Help
   -op1     -op1      -op1
   -op2     -op2      -op2
       

To set an action (show the menu associated with that action) I use:

menuBar->setActiveAction(mymenuactionpointer);

As I know, I can use one of the following to get a list of pointers to the elements of QMenuBar:

QMenuBar::actions();

or

QList<Object*> lst1 = QMenuBar::findChildren<QObject*>();

QList<Object*> lst2 = QMenuBar::findChildren<QAction*>();

When I use QMenuBar::findChildren<QAction*>() or MenuBar::actions() I got a list of the menus in menubar, I mean, I got "File, Edit, Help" from my QMenuBar, the size of the QList in this case is 3.

When I use QMenuBar::findChildren<QObject*>() I got a list of QObject of size 6, which is the correct number of items in the menu bar. However, I have tried cast to QAction*

QAction *a = (QAction *)lst1.at(0);
QAction *a = qobject_cast<QAction*>(lst1.at(0));
QAction *a = dynamic_cast<QAction*>(lst1.at(0));

In all this cases a is not NULL, but when I try to get the action name QAction::title() it always causes me segmentation fault.

I have been searching and I found here that after getting the menubar actions list, one can ask to QAction::menu() (which returns a valid QMenu pointer if the item is a menu) to know if the item is a QMenu, if yes, one can repeat getting the actions list of that menu, and continue iterating. But this does not work for me, I expected that for

QList<Object*> lst2 = QMenuBar::findChildren<QAction*>();

each element "File, Edit Help" QAction::menu() returns a valid menu pointer, so I could get the list of the actions of each menu, but this does not work at all for me.

Answer 1

The correct way to enumerate a QMenu is to use the actions() functions, but there is a catch - some of the actions are submenus, and they need to be iterated recursively. In fact, each QMenu is associated with a QAction, and they both hold pointers to each other - see QMenu::menuAction() and QAction::menu().

It is crucial to understand that each QMenu is also associated with a QAction. So knowing that, the proper implementation is the following:

void enumerateMenu(QMenu *menu)
{
    foreach (QAction *action, menu->actions()) {
        if (action->isSeparator()) {
            qDebug("this action is a separator");
        } else if (action->menu()) {
            qDebug("action: %s", qUtf8Printable(action->text()));
            qDebug(">>> this action is associated with a submenu, iterating it recursively...");
            enumerateMenu(action->menu());
            qDebug("<<< finished iterating the submenu");
        } else {
            qDebug("action: %s", qUtf8Printable(action->text()));
        }
    }
}

Answer 2

Below is how to iterate through every menu item in the menu bar, it will also seek out any menus underneath so there is not need for recursive calling here.

// assuming you have a private QActionGroup* actions; defined in the header..
// ...and a slot named 'onAction(QAction*)' as well... this should work:
QList<QMenu*> lst;
lst = ui->menuBar->findChildren<QMenu*>();
actions = new QActionGroup(this);
foreach (QMenu* m, lst)
{
    foreach (QAction* a, m->actions())
    {
        actions->addAction(a);
    }
}
connect(actions,SIGNAL(triggered(QAction*)),this,SLOT(onAction(QAction*)));

As you can see, you can then connect a master slot to handle the various events an action might bring up (i just showed triggered here but you get the idea). Hope this helps.. someone..

Notes I used the QActionGroup for example purposes on using the list you might iterate through, but you really shouldnt use that unless you are dealing with radio groups since thats what its for. Secondly, if you want the actions because you plan to link them into a single method to handle all items, i suggest you use QMenu's triggered/hovering signals or if you need to know when a menu is about to pop up, you'll need QMenuBar's aboutToShow() signal. I cant think of a reason (for me anyway) that you cant do what you need in those signals since you are passed the QAction* in the slot. But if you MUST do it the otherway, you can do it the way I showed above, you just might not want to use the QActionGroup because of radio grouping is what it is designed for. (you can work around that by not adding items that are 'checkable' into the group.

Answer 3

The reason the qobject_cast is failing is that there are only three QActions with the QMenuBar as the parent. The other three are different QObjects (my guess is the three QMenus), so the cast fails. The QActions associated with those menus are then under those, not the root QMenuBar. I fail to see why you can't build a master list of QActions by recursively iterating through the QMenus.

You may be able to just use the QAction pointer from your UI definition if you are after a known menu, that might not trigger the parent menus. If you are trying to automate testing, trigger() on your desired QAction is probably as detailed as you need. If you are trying to do things in response to user actions, modifying toolbars is probably a better means of contextual feedback, as it doesn't break focus. Some more details on what you're actually trying to accomplish would help.

Answer 4

this puts it all together:

template <class Function>
class QMenuBarIterator {
    QMenuBar    *i_barP;

    void    iterate_sub(Function f, size_t tabsL, QMenu* m) {
        foreach (QAction *action, m->actions()) {
            f(tabsL, action);

            if (action->menu()) {
                iterate_sub(f, tabsL + 1, action->menu());
            }
        }
    }

    public:
    QMenuBarIterator(QMenuBar *barP) : i_barP(barP) {}

    virtual void operator()(size_t levelL, QAction *actionP) {
    }

    void    iterate(Function f) {
        QList<QMenu *>  menuBar = i_barP->findChildren<QMenu *>();

        foreach (QMenu* m, menuBar) {
            f(0, m->menuAction());
            iterate_sub(f, 1, m);
        }
    }
};

/***************************************************************************/
class CMenuLogger {
    public:

    void operator()(size_t tabsL, QAction *action) {
        SuperString     tabStr(GetIndentString(tabsL)); //  returns a string with tabsL tab characters in it

        if (action->isSeparator()) {
            qDebug("%s-------------------", tabStr.utf8Z());

        } else {
            qDebug("%s%s (%s)",
                tabStr.utf8Z(),
                qUtf8Printable(action->text()),
                qUtf8Printable(action->objectName()));
        }
    }
};

then in your main:

{
    QMenuBarIterator<CMenuLogger>           bar(ui->menuBar);

    bar.iterate(CMenuLogger());
}