randomlistmodel.cpp Example File | Qt Core 5.6

Qt 5.6 | Qt Core | Contiguous Cache Example | randomlistmodel.cpp Example File

Qt 5.6.2 Reference Documentation

# randomlistmodel.cpp Example File

tools/contiguouscache/randomlistmodel.cpp

      /****************************************************************************
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      ** Contact: http://www.qt.io/licensing/
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      ** This file is part of the examples of the Qt Toolkit.
      **
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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);
      }