<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html> <html lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <!-- threading.qdoc --> <title>Qt Quick Examples - Threading | Qt Quick 5.9</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 5.9</td><td ><a href="qtquick-index.html">Qt Quick</a></td><td >Qt Quick Examples - Threading</td></tr></table><table class="buildversion"><tr> <td id="buildversion" width="100%" align="right">Qt 5.9.4 Reference Documentation</td> </tr></table> </div> </div> <div class="content"> <div class="line"> <div class="content mainContent"> <div class="sidebar"> <div class="toc"> <h3><a name="toc">Contents</a></h3> <ul> <li class="level1"><a href="#running-the-example">Running the Example</a></li> <li class="level1"><a href="#threaded-listmodel">Threaded ListModel</a></li> <li class="level1"><a href="#workerscript">WorkerScript</a></li> </ul> </div> <div class="sidebar-content" id="sidebar-content"></div></div> <h1 class="title">Qt Quick Examples - Threading</h1> <span class="subtitle"></span> <!-- $$$threading-description --> <div class="descr"> <a name="details"></a> <p class="centerAlign"><img src="images/qml-threading-example.png" alt="" /></p><p><i>Threading</i> is a collection of QML multithreading examples.</p> <a name="running-the-example"></a> <h2 id="running-the-example">Running the Example</h2> <p>To run the example from Qt Creator, open the <b>Welcome</b> mode and select the example from <b>Examples</b>. For more information, visit Building and Running an Example.</p> <a name="threaded-listmodel"></a> <h2 id="threaded-listmodel">Threaded ListModel</h2> <p><i>Threaded ListModel</i> contains a <a href="qml-qtquick-listview.html">ListView</a> and a ListModel. The ListModel object is updated asynchronously in another thread, and the results propagate back to the main thread. A timer requests updates from the worker thread periodically:</p> <pre class="qml"> <span class="type">Timer</span> { <span class="name">id</span>: <span class="name">timer</span> <span class="name">interval</span>: <span class="number">2000</span>; <span class="name">repeat</span>: <span class="number">true</span> <span class="name">running</span>: <span class="number">true</span> <span class="name">triggeredOnStart</span>: <span class="number">true</span> <span class="name">onTriggered</span>: { var <span class="name">msg</span> = {'action': <span class="string">'appendCurrentTime'</span>, 'model': <span class="name">listModel</span>}; <span class="name">worker</span>.<span class="name">sendMessage</span>(<span class="name">msg</span>); } } </pre> <p>Inside the worker thread, the ListModel is synchronized once the data is finished loading:</p> <pre class="js"> <span class="name">WorkerScript</span>.<span class="name">onMessage</span> <span class="operator">=</span> <span class="keyword">function</span>(<span class="name">msg</span>) { <span class="keyword">if</span> (<span class="name">msg</span>.<span class="name">action</span> <span class="operator">==</span> <span class="string">'appendCurrentTime'</span>) { var <span class="name">data</span> = {'time': new <span class="name">Date</span>().<span class="name">toTimeString</span>()}; <span class="name">msg</span>.<span class="name">model</span>.<span class="name">append</span>(<span class="name">data</span>); <span class="name">msg</span>.<span class="name">model</span>.<span class="name">sync</span>(); <span class="comment">// updates the changes to the list</span> } } </pre> <a name="workerscript"></a> <h2 id="workerscript">WorkerScript</h2> <p><i>WorkerScript</i> contains an example of using a <a href="qtquick-threading-example.html#workerscript">WorkerScript</a> to offload expensive calculations into another thread. This keeps the UI from being blocked. This example calculates numbers in Pascal's Triangle, and not in a very optimal way, so it will often take several seconds to complete the calculation. By doing this in a <a href="qtquick-threading-example.html#workerscript">WorkerScript</a> in another thread, the UI is not blocked during this time.</p> <p>When the UI needs another value, a request is sent to the <a href="qtquick-threading-example.html#workerscript">WorkerScript</a>:</p> <pre class="qml"> <span class="type">Spinner</span> { <span class="name">id</span>: <span class="name">rowSpinner</span> <span class="name">label</span>: <span class="string">"Row"</span> <span class="name">onValueChanged</span>: { <span class="name">resultText</span>.<span class="name">text</span> <span class="operator">=</span> <span class="string">"Loading..."</span>; <span class="name">myWorker</span>.<span class="name">sendMessage</span>( { row: <span class="name">rowSpinner</span>.<span class="name">value</span>, column: <span class="name">columnSpinner</span>.<span class="name">value</span> } ); } } </pre> <p>The workerscript then is free to take a really long time to calculate it:</p> <pre class="js"> <span class="name">WorkerScript</span>.<span class="name">onMessage</span> <span class="operator">=</span> <span class="keyword">function</span>(<span class="name">message</span>) { <span class="comment">//Calculate result (may take a while, using a naive algorithm)</span> var <span class="name">calculatedResult</span> = <span class="name">triangle</span>(<span class="name">message</span>.<span class="name">row</span>, <span class="name">message</span>.<span class="name">column</span>); <span class="comment">//Send result back to main thread</span> <span class="name">WorkerScript</span>.<span class="name">sendMessage</span>( { row: <span class="name">message</span>.<span class="name">row</span>, column: <span class="name">message</span>.<span class="name">column</span>, result: <span class="name">calculatedResult</span>} ); } </pre> <p>When it's done, the result returns to the main scene via the <a href="qtquick-threading-example.html#workerscript">WorkerScript</a> type:</p> <pre class="qml"> <span class="type">WorkerScript</span> { <span class="name">id</span>: <span class="name">myWorker</span> <span class="name">source</span>: <span class="string">"workerscript.js"</span> <span class="name">onMessage</span>: { <span class="keyword">if</span> (<span class="name">messageObject</span>.<span class="name">row</span> <span class="operator">==</span> <span class="name">rowSpinner</span>.<span class="name">value</span> <span class="operator">&&</span> <span class="name">messageObject</span>.<span class="name">column</span> <span class="operator">==</span> <span class="name">columnSpinner</span>.<span class="name">value</span>){ <span class="comment">//Not an old result</span> <span class="keyword">if</span> (<span class="name">messageObject</span>.<span class="name">result</span> <span class="operator">==</span> -<span class="number">1</span>) <span class="name">resultText</span>.<span class="name">text</span> <span class="operator">=</span> <span class="string">"Column must be <= Row"</span>; <span class="keyword">else</span> <span class="name">resultText</span>.<span class="name">text</span> <span class="operator">=</span> <span class="name">messageObject</span>.<span class="name">result</span>; } } } </pre> <p>Files:</p> <ul> <li><a href="qtquick-threading-threading-qml.html">threading/threading.qml</a></li> <li><a href="qtquick-threading-threadedlistmodel-dataloader-js.html">threading/threadedlistmodel/dataloader.js</a></li> <li><a href="qtquick-threading-threadedlistmodel-timedisplay-qml.html">threading/threadedlistmodel/timedisplay.qml</a></li> <li><a href="qtquick-threading-workerscript-spinner-qml.html">threading/workerscript/Spinner.qml</a></li> <li><a href="qtquick-threading-workerscript-workerscript-js.html">threading/workerscript/workerscript.js</a></li> <li><a href="qtquick-threading-workerscript-workerscript-qml.html">threading/workerscript/workerscript.qml</a></li> <li><a href="qtquick-threading-main-cpp.html">threading/main.cpp</a></li> <li><a href="qtquick-threading-threading-pro.html">threading/threading.pro</a></li> <li><a href="qtquick-threading-threading-qmlproject.html">threading/threading.qmlproject</a></li> <li><a href="qtquick-threading-threading-qrc.html">threading/threading.qrc</a></li> <li><a href="qtquick-threading-threadedlistmodel-threadedlistmodel-qmlproject.html">threading/threadedlistmodel/threadedlistmodel.qmlproject</a></li> <li><a href="qtquick-threading-workerscript-workerscript-qmlproject.html">threading/workerscript/workerscript.qmlproject</a></li> </ul> </div> <!-- @@@threading --> </div> </div> </div> </div> </div> <div class="footer"> <p> <acronym title="Copyright">©</acronym> 2017 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>