QComboBox elided text on selected item

Question

So, I have a QComboBox.

If the currentText() is too long for the widget then I want to show an ellipsis.

Like this :

So :

void MyComboBox::paintEvent(QPaintEvent * )
{
      QStylePainter painter(this);
      QStyleOptionComboBox opt;
      initStyleOption(&opt);
      painter.drawComplexControl(QStyle::CC_ComboBox, opt);

      QRect rect = this->rect();
      //this is not ideal
      rect.setLeft(rect.left() + 7);
      rect.setRight(rect.width() - 15);
      //

      QTextOption option;
      option.setAlignment(Qt::AlignVCenter);

      QFontMetrics fontMetric(painter.font());
      const QString elidedText = QAbstractItemDelegate::elidedText(fontMetric, rect.width(), Qt::ElideRight, this->currentText());
      painter.drawText( rect, elidedText, option);
}

This is working flawlessy. The problem is the code in between the comments, because I am hardcoding the distances from the left and right border. It makes me cringe.

The result without that code is:

Does anybody know a more general way to do this, without hardcoding? Thank you

Answer 1

Where the text should be drawn exactly depends on the used style. You can get information about (some of) the positioning of subelements with QStyle::subControlRect. The subcontrol that matches the combo box text best seems to be QStyle::SC_ComboBoxEditField, though if the item has an icon, this needs to be taken into account as well. If the items do not have icons, you can go with

  QRect textRect = style()->subControlRect(QStyle::CC_ComboBox, &opt, QStyle::SC_ComboBoxEditField, this);
  QFontMetrics fontMetric(painter.font());
  const QString elidedText = QAbstractItemDelegate::elidedText(fontMetric, textRect.width(), Qt::ElideRight, this->currentText());
  opt.currentText = elidedText;
  painter.drawControl(QStyle::CE_ComboBoxLabel, opt);

You might want to have a look at how e.g. QFusionStyle::drawControl works for details.

In general, if you want all your combo boxes to elide the text, you should consider implementing your own QProxyStyle and only override MyStyle::drawControl for QStyle::CE_ComboBoxLabel.

Answer 2

This is the solution I've been using:

void CustomComboBox::paintEvent(QPaintEvent * /*event*/)
{
    QStyleOptionComboBox opt;
    initStyleOption(&opt);

    QStylePainter p(this);
    p.drawComplexControl(QStyle::CC_ComboBox, opt);

    QRect textRect = style()->subControlRect(QStyle::CC_ComboBox, &opt, QStyle::SC_ComboBoxEditField, this);
    opt.currentText = p.fontMetrics().elidedText(opt.currentText, Qt::ElideRight, textRect.width());
    p.drawControl(QStyle::CE_ComboBoxLabel, opt);
}

This approach is very similar to a combination of your sample code and the snippet E4z9 suggested. I just thought I'd include the whole method for others coming here in the future.