How to make QComboBox popup upwards?

问题

my QComboBox-derived class lives in a QGraphicsScene at the bottom end of the (visible) screen - but it pops up downwards, thus out of view.

(How) is it possible to force the popup to open above the widget?

I've tried re-implementing showPopup like this:

void MyComboBox::showPopup()
{
     QAbstractItemView *popupView = view();
     popupView->move(0,-100);
     //popupView->window->move(0,-100);
     QComboBox::showPopup();
}

The result is, that the content seems to be shifted, but not the underlying popup object. I think it might be possible to find a solution with styles as indicated in this article, but I can't find any Styles control that might be helpful here. I am rather new to C++ as well as Qt, so I might be missing something obvious.

I'd appreciate any help on this matter!

Best regards,

Sebastian

回答1:

With the information found here, I was able to get it done this way:

void SteuerQComboBox::showPopup() {
    QComboBox::showPopup();
    QWidget *popup = this->findChild<QFrame*>(); 
    popup->move(popup->x(),popup->y()-this->height()-popup->height());
}

Note that it's crucially important to call the base classes "showPopup" first.

Thanks to everybody who was reading my question and thinking about it!

回答2:

user1319422's solution isn't bad, but it has two problems.

If your platform has GUI animation, the listbox will animate opening downwards, then is moved above the text box.
If you disable combobox animation (or you don't have it), the call to QComboBox::showPopup() still makes the GUI element start to appear on the screen already. So, moving it there would cause it to flicker as it appears in the first place and moves to the next.

So, to address the first problem, I just switched off animation:

void MyComboBox::showPopup()
{
  bool oldAnimationEffects = qApp->isEffectEnabled(Qt::UI_AnimateCombo);
  qApp->setEffectEnabled(Qt::UI_AnimateCombo, false);

  QComboBox::showPopup();
  qApp->setEffectEnabled(Qt::UI_AnimateCombo, oldAnimationEffects);
}

Then, for the second problem, I moved the frame in the Show event:

bool MyComboBox::eventFilter(QObject *o, QEvent *e)
{
  bool handled = false;
  if (e->type() == QEvent::Show)
  {
    if (o == view())
    {
      QWidget *frame = findChild<QFrame*>(); 

      //For some reason, the frame's geometry is GLOBAL, not relative to the QComboBox!
      frame->move(frame->x(),
                  mapToGlobal(lineEdit()->geometry().topLeft()).y() - frame->height());
    }
  }
  /*else if other filters here*/

  if (!handled)
    handled = QComboBox::eventFilter(o, e);

  return handled;
}

回答3:

if you want to force popup to open above only when it is out of view you can do this:

void SteuerQComboBox::showPopup() {
    QComboBox::showPopup();
    QWidget *popup = this->findChild<QFrame*>(); 

    if((popup->y() + popup->height()) > this->window()->height())
        popup->move(popup->x(),popup->y()-this->height()-popup->height());
}

来源：https://stackoverflow.com/questions/10057140/how-to-make-qcombobox-popup-upwards

标签

popup

stylesheet

qcombobox