Prevent a QMenu from closing when one of its QAction is triggered

Question

I\'m using a QMenu as context menu. This menu is filled with QActions. One of these QActions is checkable, and I\'d like to be able to check/uncheck it without closing the c

Answer 1

Here are couple ideas I've had... Not sure at all they will work tho ;)

1) Try to catch the Event by using the QMenu's method aboutToHide(); Maybe you can "Cancel" the hide process ?

2) Maybe you could consider using an EventFilter ?

Try to have a look at : http://qt.nokia.com/doc/4.6/qobject.html#installEventFilter

3) Otherwise you could reimplement QMenu to add your own behavior, but it seems a lot of work to me...

Hope this helps a bit !

Answer 2

Starting from baysmith solution, the checkbox didn´t work as I was expecting, because I was connecting to the action triggered(), rather than connecting to the checkbox toggled(bool). I´m using the code to open a menu with several checkboxes when I press a button :

           QMenu menu;

            QCheckBox *checkBox = new QCheckBox("Show Grass", &menu);
            checkBox->setChecked(m_showGrass);
            QWidgetAction *action = new QWidgetAction(&menu);
            action->setDefaultWidget(checkBox);
            menu.addAction(action);
            //connect(action, SIGNAL(triggered()), this, SLOT(ToggleShowHardscape_Grass()));
            connect(checkBox, SIGNAL(toggled(bool)), this, SLOT(ToggleShowHardscape_Grass()));

            menu.exec(QCursor::pos() + QPoint(-300, 20));

For my use case, this works like a charm

Answer 3

There doesn't seem to be any elegant way to prevent the menu from closing. However, the menu will only close if the action can actually trigger, i.e. it is enabled. So, the most elegant solution I found is to trick the menu by shortly disabling the action at the moment when it would be triggered.

1. Subclass QMenu
2. Reimplement relevant event handlers (like mouseReleaseEvent())
3. In the event handler, disable the action, then call base class' implementation, then enable the action again, and trigger it manually

This is an example of reimplemented mouseReleaseEvent():

void mouseReleaseEvent(QMouseEvent *e)
{
    QAction *action = activeAction();
    if (action && action->isEnabled()) {
        action->setEnabled(false);
        QMenu::mouseReleaseEvent(e);
        action->setEnabled(true);
        action->trigger();
    }
    else
        QMenu::mouseReleaseEvent(e);
}

To make the solution perfect, similar should be done in all event handlers that may trigger the action, like keyPressEvent(), etc...

The trouble is that it is not always easy to know whether your reimplementation should actually trigger the action, or even which action should be triggered. The most difficult is probably action triggering by mnemonics: you would need to reimplement the complex algorithm in QMenu::keyPressEvent() yourself.

Answer 4

(I started with Andy's answer, so thank you Andy!)

1) aboutToHide() works, by re-popping the menu at a cached position, BUT it can also enter an infinite loop. Testing if the mouse is clicked outside the menu to ignore re-opening should do the trick.

2) I tried an event filter but it blocks the actual click to the menu item.

3) Use both.

Here is a dirty pattern to prove that it works. This keeps the menu open when the user holds down CTRL when clicking:

    # in __init__ ...
    self.options_button.installEventFilter(self)
    self.options_menu.installEventFilter(self)
    self.options_menu.aboutToHide.connect(self.onAboutToHideOptionsMenu)

    self.__options_menu_pos_cache = None
    self.__options_menu_open = False

def onAboutToHideOptionsMenu(self):
    if self.__options_menu_open:          # Option + avoid an infinite loop
        self.__options_menu_open = False  # Turn it off to "reset"
        self.options_menu.popup(self.__options_menu_pos_cache)

def eventFilter(self, obj, event):
    if event.type() == QtCore.QEvent.MouseButtonRelease:
        if obj is self.options_menu:
            if event.modifiers() == QtCore.Qt.ControlModifier:
                self.__options_menu_open = True

            return False

        self.__options_menu_pos_cache = event.globalPos()
        self.options_menu.popup(event.globalPos())
        return True

    return False

I say it is dirty because the widget here is acting as an event filter for both the button that opens the menu as well as the menu itself. Using explicit event filter classes would be easy enough to add and it would make things a little easier to follow.

The bools could probably be replaced with a check to see if the mouse is over the menu, and if not, don't pop it open. However, the CTRL key still has to be factored in for my use case, so it probably isn't far off a nice solution as it is.

When the user holds down CTRL and clicks on the menu, it flips a switch so the menu opens itself back up when it tried to close. The position is cached so it opens at the same position. There is a quick flicker, but it feels OK since the user knows they are holding a key down to make this work.

At the end of the day (literally) I already had the whole menu doing the right thing. I just wanted to add this functionality and I definitely didn't want to change to using a widget just for this. For this reason, I am keeping even this dirty patch for now.

Answer 5

Use a QWidgetAction and QCheckBox for a "checkable action" which doesn't cause the menu to close.

QCheckBox *checkBox = new QCheckBox(menu);
QWidgetAction *checkableAction = new QWidgetAction(menu);
checkableAction->setDefaultWidget(checkBox);
menu->addAction(checkableAction);

In some styles, this won't appear exactly the same as a checkable action. For example, for the Plastique style, the check box needs to be indented a bit.

Answer 6

This is my solution:

    // this menu don't hide, if action in actions_with_showed_menu is chosen.
    class showed_menu : public QMenu
    {
      Q_OBJECT
    public:
      showed_menu (QWidget *parent = 0) : QMenu (parent) { is_ignore_hide = false; }
      showed_menu (const QString &title, QWidget *parent = 0) : QMenu (title, parent) { is_ignore_hide = false; }
      void add_action_with_showed_menu (const QAction *action) { actions_with_showed_menu.insert (action); }

      virtual void setVisible (bool visible)
      {
        if (is_ignore_hide)
          {
            is_ignore_hide = false;
            return;
          }
        QMenu::setVisible (visible);
      }

      virtual void mouseReleaseEvent (QMouseEvent *e)
      {
        const QAction *action = actionAt (e->pos ());
        if (action)
          if (actions_with_showed_menu.contains (action))
            is_ignore_hide = true;
        QMenu::mouseReleaseEvent (e);
      }
    private:
      // clicking on this actions don't close menu 
      QSet <const QAction *> actions_with_showed_menu;
      bool is_ignore_hide;
    };

    showed_menu *menu = new showed_menu ();
    QAction *action = menu->addAction (new QAction (menu));
    menu->add_action_with_showed_menu (action);