- Qt 5.5
- Qt Core
- Contiguous Cache Example
- randomlistmodel.cpp Example File
- Qt 5.5.1 Reference Documentation

# randomlistmodel.cpp Example File

tools/contiguouscache/randomlistmodel.cpp

    /****************************************************************************
    **
    ** Copyright (C) 2015 The Qt Company Ltd.
    ** Contact: http://www.qt.io/licensing/
    **
    ** This file is part of the examples of the Qt Toolkit.
    **
    ** $QT_BEGIN_LICENSE:BSD$
    ** You may use this file under the terms of the BSD license as follows:
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    #include "randomlistmodel.h"
    #include <stdlib.h>

    static const int bufferSize(500);
    static const int lookAhead(100);
    static const int halfLookAhead(lookAhead/2);

    RandomListModel::RandomListModel(QObject *parent)
    : QAbstractListModel(parent), m_rows(bufferSize), m_count(10000)
    {
    }

    RandomListModel::~RandomListModel()
    {
    }

    int RandomListModel::rowCount(const QModelIndex &) const
    {
        return m_count;
    }

    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));
    }

    QString RandomListModel::fetchRow(int position) const
    {
        return QString::number(rand() % ++position);
    }