#include <QtWidgets>
#include <QTimer>

class Delegate final
  : public QStyledItemDelegate
{
public:
  explicit Delegate (QObject * parent = nullptr)
    : QStyledItemDelegate {parent}
  {
  }

  void paint (QPainter * painter, QStyleOptionViewItem const& option
              , QModelIndex const& index) const
  {
    QStyleOptionProgressBar progress_bar_option;
    progress_bar_option.rect = option.rect;
    progress_bar_option.state = QStyle::State_Enabled;
    progress_bar_option.direction = QApplication::layoutDirection ();
    progress_bar_option.fontMetrics = QApplication::fontMetrics ();
    progress_bar_option.minimum = 0;
    progress_bar_option.maximum = 100;
    auto progress = index.data ().toLongLong ();
    auto percent = int (progress * 100 / index.data (Qt::UserRole).toLongLong ());
    progress_bar_option.progress = percent;
    progress_bar_option.text = QString::number (percent) + '%';
    progress_bar_option.textVisible = true;
    progress_bar_option.textAlignment = Qt::AlignCenter;
    QApplication::style ()->drawControl (QStyle::CE_ProgressBar, &progress_bar_option, painter);
  }
};

int main (int argc, char * argv[])
{
  QApplication a {argc, argv};
  QListWidget w;
  Delegate d;
  w.setItemDelegate (&d);
  QListWidgetItem i1 {"Item 1"};
  i1.setData (Qt::UserRole, 100);
  w.addItem (&i1);
  QListWidgetItem i2 {"Item 2"};
  w.addItem (&i2);
  i2.setData (Qt::UserRole, 100);
  w.show ();
  QTimer t;
  qint64 n1 {0};
  qint64 n2 {0};
  t.callOnTimeout ([&] {
                     i1.setData (Qt::DisplayRole, (n1 += 2));
                     i2.setData (Qt::DisplayRole, (n2 += 10));
                    });
  t.start (1000);
  QObject::connect (&a, &QApplication::lastWindowClosed, &a, &QApplication::quit);
  return a.exec ();
}