1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
|
// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
#include "randomlistmodel.h"
#include <QRandomGenerator>
static constexpr int bufferSize(500);
static constexpr int lookAhead(100);
static constexpr int halfLookAhead(lookAhead / 2);
RandomListModel::RandomListModel(QObject *parent)
: QAbstractListModel(parent), m_rows(bufferSize), m_count(10000)
{
}
int RandomListModel::rowCount(const QModelIndex &) const
{
return m_count;
}
//! [0]
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));
}
//![0]
//![1]
QString RandomListModel::fetchRow(int position) const
{
return QString::number(QRandomGenerator::global()->bounded(++position));
}
//![1]
|
