Qt 4.8: randomlistmodel.cpp Example File (tools/contiguouscache/randomlistmodel.cpp)

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# randomlistmodel.cpp Example File

tools/contiguouscache/randomlistmodel.cpp

     /****************************************************************************
     **
     ** Copyright (C) 2012 Digia Plc and/or its subsidiary(-ies).
     ** Contact: http://www.qt-project.org/legal
     **
     ** 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:
     **
     ** "Redistribution and use in source and binary forms, with or without
     ** modification, are permitted provided that the following conditions are
     ** met:
     **   * Redistributions of source code must retain the above copyright
     **     notice, this list of conditions and the following disclaimer.
     **   * Redistributions in binary form must reproduce the above copyright
     **     notice, this list of conditions and the following disclaimer in
     **     the documentation and/or other materials provided with the
     **     distribution.
     **   * Neither the name of Digia Plc and its Subsidiary(-ies) nor the names
     **     of its contributors may be used to endorse or promote products derived
     **     from this software without specific prior written permission.
     **
     **
     ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
     ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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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);
     }