Home · All Classes · All Functions · Overviews

randomlistmodel.cpp Example File
tools/contiguouscache/randomlistmodel.cpp

 /****************************************************************************
 **
 ** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
 ** All rights reserved.
 ** Contact: Nokia Corporation ([email protected])
 **
 ** This file is part of the examples of the Qt Toolkit.
 **
 ** $QT_BEGIN_LICENSE:LGPL$
 ** Commercial Usage
 ** Licensees holding valid Qt Commercial licenses may use this file in
 ** accordance with the Qt Commercial License Agreement provided with the
 ** Software or, alternatively, in accordance with the terms contained in
 ** a written agreement between you and Nokia.
 **
 ** GNU Lesser General Public License Usage
 ** Alternatively, this file may be used under the terms of the GNU Lesser
 ** General Public License version 2.1 as published by the Free Software
 ** Foundation and appearing in the file LICENSE.LGPL included in the
 ** packaging of this file.  Please review the following information to
 ** ensure the GNU Lesser General Public License version 2.1 requirements
 ** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
 **
 ** In addition, as a special exception, Nokia gives you certain additional
 ** rights.  These rights are described in the Nokia Qt LGPL Exception
 ** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
 **
 ** GNU General Public License Usage
 ** Alternatively, this file may be used under the terms of the GNU
 ** General Public License version 3.0 as published by the Free Software
 ** Foundation and appearing in the file LICENSE.GPL included in the
 ** packaging of this file.  Please review the following information to
 ** ensure the GNU General Public License version 3.0 requirements will be
 ** met: http://www.gnu.org/copyleft/gpl.html.
 **
 ** If you have questions regarding the use of this file, please contact
 ** Nokia at [email protected].
 ** $QT_END_LICENSE$
 **
 ****************************************************************************/
 #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);
 }