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++ // Copyright (C) 2016 The Qt Company Ltd.
++ // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
++ #include "randomlistmodel.h"
++ #include <QRandomGenerator>
++
++ static constexpr int bufferSize(500);
++ static constexpr int lookAhead(100);
++ static constexpr int halfLookAhead(lookAhead / 2);
++
++ RandomListModel::RandomListModel(QObject *parent)
++ : QAbstractListModel(parent), m_rows(bufferSize), m_count(10000)
++ {
++ }
++
++ int RandomListModel::rowCount(const QModelIndex &) const
++ {
++ return m_count;
++ }
++
++ //! [0]
++ QVariant RandomListModel::data(const QModelIndex &index, int role) const
++ {
++ if (role != Qt::DisplayRole)
++ return QVariant();
++
++ int row = index.row();
++
++ if (row > m_rows.lastIndex()) {
++ if (row - m_rows.lastIndex() > lookAhead)
++ cacheRows(row - halfLookAhead, qMin(m_count, row + halfLookAhead));
++ else while (row > m_rows.lastIndex())
++ m_rows.append(fetchRow(m_rows.lastIndex() + 1));
++ } else if (row < m_rows.firstIndex()) {
++ if (m_rows.firstIndex() - row > lookAhead)
++ cacheRows(qMax(0, row - halfLookAhead), row + halfLookAhead);
++ else while (row < m_rows.firstIndex())
++ m_rows.prepend(fetchRow(m_rows.firstIndex() - 1));
++ }
++
++ return m_rows.at(row);
++ }
++
++ void RandomListModel::cacheRows(int from, int to) const
++ {
++ for (int i = from; i <= to; ++i)
++ m_rows.insert(i, fetchRow(i));
++ }
++ //![0]
++
++ //![1]
++ QString RandomListModel::fetchRow(int position) const
++ {
++ return QString::number(QRandomGenerator::global()->bounded(++position));
++ }
++ //![1]