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50#include "randomlistmodel.h"
51#include <QRandomGenerator>
52
53static const int bufferSize(500);
54static const int lookAhead(100);
55static const int halfLookAhead(lookAhead/2);
56
57RandomListModel::RandomListModel(QObject *parent)
58: QAbstractListModel(parent), m_rows(bufferSize), m_count(10000)
59{
60}
61
62RandomListModel::~RandomListModel()
63{
64}
65
66int RandomListModel::rowCount(const QModelIndex &) const
67{
68 return m_count;
69}
70
71//! [0]
72QVariant RandomListModel::data(const QModelIndex &index, int role) const
73{
74 if (role != Qt::DisplayRole)
75 return QVariant();
76
77 int row = index.row();
78
79 if (row > m_rows.lastIndex()) {
80 if (row - m_rows.lastIndex() > lookAhead)
81 cacheRows(row-halfLookAhead, qMin(a: m_count, b: row+halfLookAhead));
82 else while (row > m_rows.lastIndex())
83 m_rows.append(value: fetchRow(m_rows.lastIndex()+1));
84 } else if (row < m_rows.firstIndex()) {
85 if (m_rows.firstIndex() - row > lookAhead)
86 cacheRows(qMax(a: 0, b: row-halfLookAhead), row+halfLookAhead);
87 else while (row < m_rows.firstIndex())
88 m_rows.prepend(value: fetchRow(m_rows.firstIndex()-1));
89 }
90
91 return m_rows.at(pos: row);
92}
93
94void RandomListModel::cacheRows(int from, int to) const
95{
96 for (int i = from; i <= to; ++i)
97 m_rows.insert(pos: i, value: fetchRow(i));
98}
99//![0]
100
101//![1]
102QString RandomListModel::fetchRow(int position) const
103{
104 return QString::number(QRandomGenerator::global()->bounded(highest: ++position));
105}
106//![1]
107

source code of qtbase/examples/corelib/tools/contiguouscache/randomlistmodel.cpp