<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html> <html lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>randomlistmodel.cpp Example File | Qt Core 5.12.6</title> <link rel="stylesheet" type="text/css" href="style/offline-simple.css" /> <script type="text/javascript"> document.getElementsByTagName("link").item(0).setAttribute("href", "style/offline.css"); // loading style sheet breaks anchors that were jumped to before // so force jumping to anchor again setTimeout(function() { var anchor = location.hash; // need to jump to different anchor first (e.g. none) location.hash = "#"; setTimeout(function() { location.hash = anchor; }, 0); }, 0); </script> </head> <body> <div class="header" id="qtdocheader"> <div class="main"> <div class="main-rounded"> <div class="navigationbar"> <table><tr> <td >Qt 5.12</td><td ><a href="qtcore-index.html">Qt Core</a></td><td ><a href="qtcore-tools-contiguouscache-example.html">Contiguous Cache Example</a></td><td >randomlistmodel.cpp Example File</td></tr></table><table class="buildversion"><tr> <td id="buildversion" width="100%" align="right"><a href="qtcore-index.html">Qt 5.12.6 Reference Documentation</a></td> </tr></table> </div> </div> <div class="content"> <div class="line"> <div class="content mainContent"> <div class="sidebar"><div class="sidebar-content" id="sidebar-content"></div></div> <h1 class="title">randomlistmodel.cpp Example File</h1> <span class="subtitle">tools/contiguouscache/randomlistmodel.cpp</span> <!-- $$$tools/contiguouscache/randomlistmodel.cpp-description --> <div class="descr"> <a name="details"></a> <pre class="cpp"> <span class="comment">/**************************************************************************** ** ** Copyright (C) 2016 The Qt Company Ltd. ** Contact: https://www.qt.io/licensing/ ** ** This file is part of the examples of the Qt Toolkit. ** ** $QT_BEGIN_LICENSE:BSD$ ** Commercial License Usage ** Licensees holding valid commercial Qt licenses may use this file in ** accordance with the commercial license agreement provided with the ** Software or, alternatively, in accordance with the terms contained in ** a written agreement between you and The Qt Company. For licensing terms ** and conditions see https://www.qt.io/terms-conditions. For further ** information use the contact form at https://www.qt.io/contact-us. ** ** BSD License Usage ** Alternatively, 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 The Qt Company Ltd 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 ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE." ** ** $QT_END_LICENSE$ ** ****************************************************************************/</span> <span class="preprocessor">#include "randomlistmodel.h"</span> <span class="preprocessor">#include <QRandomGenerator></span> <span class="preprocessor">#include <stdlib.h></span> <span class="keyword">static</span> <span class="keyword">const</span> <span class="type">int</span> bufferSize(<span class="number">500</span>); <span class="keyword">static</span> <span class="keyword">const</span> <span class="type">int</span> lookAhead(<span class="number">100</span>); <span class="keyword">static</span> <span class="keyword">const</span> <span class="type">int</span> halfLookAhead(lookAhead<span class="operator">/</span><span class="number">2</span>); RandomListModel<span class="operator">::</span>RandomListModel(<span class="type"><a href="qobject.html">QObject</a></span> <span class="operator">*</span>parent) : <span class="type"><a href="qabstractlistmodel.html">QAbstractListModel</a></span>(parent)<span class="operator">,</span> m_rows(bufferSize)<span class="operator">,</span> m_count(<span class="number">10000</span>) { } RandomListModel<span class="operator">::</span><span class="operator">~</span>RandomListModel() { } <span class="type">int</span> RandomListModel<span class="operator">::</span>rowCount(<span class="keyword">const</span> <span class="type"><a href="qmodelindex.html">QModelIndex</a></span> <span class="operator">&</span>) <span class="keyword">const</span> { <span class="keyword">return</span> m_count; } <span class="type"><a href="qvariant.html">QVariant</a></span> RandomListModel<span class="operator">::</span>data(<span class="keyword">const</span> <span class="type"><a href="qmodelindex.html">QModelIndex</a></span> <span class="operator">&</span>index<span class="operator">,</span> <span class="type">int</span> role) <span class="keyword">const</span> { <span class="keyword">if</span> (role <span class="operator">!</span><span class="operator">=</span> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>DisplayRole) <span class="keyword">return</span> <span class="type"><a href="qvariant.html">QVariant</a></span>(); <span class="type">int</span> row <span class="operator">=</span> index<span class="operator">.</span>row(); <span class="keyword">if</span> (row <span class="operator">></span> m_rows<span class="operator">.</span>lastIndex()) { <span class="keyword">if</span> (row <span class="operator">-</span> m_rows<span class="operator">.</span>lastIndex() <span class="operator">></span> lookAhead) cacheRows(row<span class="operator">-</span>halfLookAhead<span class="operator">,</span> <a href="qtglobal.html#qMin">qMin</a>(m_count<span class="operator">,</span> row<span class="operator">+</span>halfLookAhead)); <span class="keyword">else</span> <span class="keyword">while</span> (row <span class="operator">></span> m_rows<span class="operator">.</span>lastIndex()) m_rows<span class="operator">.</span>append(fetchRow(m_rows<span class="operator">.</span>lastIndex()<span class="operator">+</span><span class="number">1</span>)); } <span class="keyword">else</span> <span class="keyword">if</span> (row <span class="operator"><</span> m_rows<span class="operator">.</span>firstIndex()) { <span class="keyword">if</span> (m_rows<span class="operator">.</span>firstIndex() <span class="operator">-</span> row <span class="operator">></span> lookAhead) cacheRows(<a href="qtglobal.html#qMax">qMax</a>(<span class="number">0</span><span class="operator">,</span> row<span class="operator">-</span>halfLookAhead)<span class="operator">,</span> row<span class="operator">+</span>halfLookAhead); <span class="keyword">else</span> <span class="keyword">while</span> (row <span class="operator"><</span> m_rows<span class="operator">.</span>firstIndex()) m_rows<span class="operator">.</span>prepend(fetchRow(m_rows<span class="operator">.</span>firstIndex()<span class="operator">-</span><span class="number">1</span>)); } <span class="keyword">return</span> m_rows<span class="operator">.</span>at(row); } <span class="type">void</span> RandomListModel<span class="operator">::</span>cacheRows(<span class="type">int</span> from<span class="operator">,</span> <span class="type">int</span> to) <span class="keyword">const</span> { <span class="keyword">for</span> (<span class="type">int</span> i <span class="operator">=</span> from; i <span class="operator"><</span><span class="operator">=</span> to; <span class="operator">+</span><span class="operator">+</span>i) m_rows<span class="operator">.</span>insert(i<span class="operator">,</span> fetchRow(i)); } <span class="type"><a href="qstring.html">QString</a></span> RandomListModel<span class="operator">::</span>fetchRow(<span class="type">int</span> position) <span class="keyword">const</span> { <span class="keyword">return</span> <span class="type"><a href="qstring.html">QString</a></span><span class="operator">::</span>number(<span class="type"><a href="qrandomgenerator.html">QRandomGenerator</a></span><span class="operator">::</span>global()<span class="operator">-</span><span class="operator">></span>bounded(<span class="operator">+</span><span class="operator">+</span>position)); } </pre> </div> <!-- @@@tools/contiguouscache/randomlistmodel.cpp --> </div> </div> </div> </div> </div> <div class="footer"> <p> <acronym title="Copyright">©</acronym> 2019 The Qt Company Ltd. Documentation contributions included herein are the copyrights of their respective owners.<br/> The documentation provided herein is licensed under the terms of the <a href="http://www.gnu.org/licenses/fdl.html">GNU Free Documentation License version 1.3</a> as published by the Free Software Foundation.<br/> Qt and respective logos are trademarks of The Qt Company Ltd. in Finland and/or other countries worldwide. All other trademarks are property of their respective owners. </p> </div> </body> </html>