void QListModel::ensureSorted(int column, Qt::SortOrder order, int start, int end)
{
    if (column != 0)
        return;

    int count = end - start + 1;
    QVector < QPair<QListWidgetItem*,int> > sorting(count);
    for (int i = 0; i < count; ++i) {
        sorting[i].first = items.at(start + i);
        sorting[i].second = start + i;
    }

    LessThan compare = (order == Qt::AscendingOrder ? &itemLessThan : &itemGreaterThan);
    std::sort(sorting.begin(), sorting.end(), compare);

    QModelIndexList oldPersistentIndexes = persistentIndexList();
    QModelIndexList newPersistentIndexes = oldPersistentIndexes;
    QList<QListWidgetItem*> tmp = items;
    QList<QListWidgetItem*>::iterator lit = tmp.begin();
    bool changed = false;
    for (int i = 0; i < count; ++i) {
        int oldRow = sorting.at(i).second;
        int tmpitepos = lit - tmp.begin();
        QListWidgetItem *item = tmp.takeAt(oldRow);
        if (tmpitepos > tmp.size())
            --tmpitepos;
        lit = tmp.begin() + tmpitepos;
        lit = sortedInsertionIterator(lit, tmp.end(), order, item);
        int newRow = qMax(lit - tmp.begin(), 0);
        lit = tmp.insert(lit, item);
        if (newRow != oldRow) {
            changed = true;
            for (int j = i + 1; j < count; ++j) {
                int otherRow = sorting.at(j).second;
                if (oldRow < otherRow && newRow >= otherRow)
                    --sorting[j].second;
                else if (oldRow > otherRow && newRow <= otherRow)
                    ++sorting[j].second;
            }
            for (int k = 0; k < newPersistentIndexes.count(); ++k) {
                QModelIndex pi = newPersistentIndexes.at(k);
                int oldPersistentRow = pi.row();
                int newPersistentRow = oldPersistentRow;
                if (oldPersistentRow == oldRow)
                    newPersistentRow = newRow;
                else if (oldRow < oldPersistentRow && newRow >= oldPersistentRow)
                    newPersistentRow = oldPersistentRow - 1;
                else if (oldRow > oldPersistentRow && newRow <= oldPersistentRow)
                    newPersistentRow = oldPersistentRow + 1;
                if (newPersistentRow != oldPersistentRow)
                    newPersistentIndexes[k] = createIndex(newPersistentRow,
                                                          pi.column(), pi.internalPointer());
            }
        }
    }

    if (changed) {
        emit layoutAboutToBeChanged();
        items = tmp;
        changePersistentIndexList(oldPersistentIndexes, newPersistentIndexes);
        emit layoutChanged();
    }
}