randomlistmodel.cpp Example File

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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);
 }