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<td >Qt 5.9</td><td ><a href="qtqml-index.html">Qt QML</a></td><td ><a href="qtqml-qmlmodule.html">QML Types</a></td><td >WorkerScript QML Type</td></tr></table><table class="buildversion"><tr>
<td id="buildversion" width="100%" align="right">Qt 5.9.4 Reference Documentation</td>
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<h3><a name="toc">Contents</a></h3>
<ul>
<li class="level1"><a href="#properties">Properties</a></li>
<li class="level1"><a href="#signals">Signals</a></li>
<li class="level1"><a href="#methods">Methods</a></li>
<li class="level1"><a href="#details">Detailed Description</a></li>
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<h1 class="title">WorkerScript QML Type</h1>
<span class="subtitle"></span>
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<p>Enables the use of threads in a Qt Quick application <a href="#details">More...</a></p>
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<div class="table"><table class="alignedsummary">
<tr><td class="memItemLeft rightAlign topAlign"> Import Statement:</td><td class="memItemRight bottomAlign"> import .</td></tr></table></div><ul>
<li><a href="qml-workerscript-members.html">List of all members, including inherited members</a></li>
</ul>
<a name="properties"></a>
<h2 id="properties">Properties</h2>
<ul>
<li class="fn"><b><b><a href="qml-workerscript.html#source-prop">source</a></b></b> : url</li>
</ul>
<a name="signals"></a>
<h2 id="signals">Signals</h2>
<ul>
<li class="fn"><b><b><a href="qml-workerscript.html#message-signal">message</a></b></b>(jsobject <i>msg</i>)</li>
</ul>
<a name="methods"></a>
<h2 id="methods">Methods</h2>
<ul>
<li class="fn"><b><b><a href="qml-workerscript.html#sendMessage-method">sendMessage</a></b></b>(jsobject <i>message</i>)</li>
</ul>
<!-- $$$WorkerScript-description -->
<a name="details"></a>
<h2 id="details">Detailed Description</h2>
<p>Use <a href="qml-workerscript.html">WorkerScript</a> to run operations in a new thread. This is useful for running operations in the background so that the main GUI thread is not blocked.</p>
<p>Messages can be passed between the new thread and the parent thread using <a href="qml-workerscript.html#sendMessage-method">sendMessage()</a> and the <code>onMessage()</code> handler.</p>
<p>An example:</p>
<pre class="qml">
import QtQuick 2.0
<span class="type">Rectangle</span> {
<span class="name">width</span>: <span class="number">300</span>; <span class="name">height</span>: <span class="number">300</span>
<span class="type">Text</span> {
<span class="name">id</span>: <span class="name">myText</span>
<span class="name">text</span>: <span class="string">'Click anywhere'</span>
}
<span class="type"><a href="qml-workerscript.html">WorkerScript</a></span> {
<span class="name">id</span>: <span class="name">myWorker</span>
<span class="name">source</span>: <span class="string">"script.js"</span>
<span class="name">onMessage</span>: <span class="name">myText</span>.<span class="name">text</span> <span class="operator">=</span> <span class="name">messageObject</span>.<span class="name">reply</span>
}
<span class="type">MouseArea</span> {
<span class="name">anchors</span>.fill: <span class="name">parent</span>
<span class="name">onClicked</span>: <span class="name">myWorker</span>.<span class="name">sendMessage</span>({ 'x': <span class="name">mouse</span>.<span class="name">x</span>, 'y': <span class="name">mouse</span>.<span class="name">y</span> })
}
}
</pre>
<p>The above worker script specifies a JavaScript file, "script.js", that handles the operations to be performed in the new thread. Here is <code>script.js</code>:</p>
<pre class="cpp">
<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">// ... long-running operations and calculations are done here</span>
<span class="name">WorkerScript</span>.<span class="name">sendMessage</span>({ 'reply': <span class="string">'Mouse is at '</span> <span class="operator">+</span> <span class="name">message</span>.<span class="name">x</span> <span class="operator">+</span> <span class="string">','</span> <span class="operator">+</span> <span class="name">message</span>.<span class="name">y</span> })
}
</pre>
<p>When the user clicks anywhere within the rectangle, <code>sendMessage()</code> is called, triggering the <code>WorkerScript.onMessage()</code> handler in <code>script.js</code>. This in turn sends a reply message that is then received by the <code>onMessage()</code> handler of <code>myWorker</code>.</p>
<a name="restrictions"></a>
<h4 >Restrictions</h4>
<p>Since the <code>WorkerScript.onMessage()</code> function is run in a separate thread, the JavaScript file is evaluated in a context separate from the main QML engine. This means that unlike an ordinary JavaScript file that is imported into QML, the <code>script.js</code> in the above example cannot access the properties, methods or other attributes of the QML item, nor can it access any context properties set on the QML object through <a href="qqmlcontext.html">QQmlContext</a>.</p>
<p>Additionally, there are restrictions on the types of values that can be passed to and from the worker script. See the <a href="qml-workerscript.html#sendMessage-method">sendMessage()</a> documentation for details.</p>
<p>Worker script can not use <a href="qtqml-javascript-imports.html">.import</a> syntax.</p>
<p><b>See also </b>Qt Quick Examples - Threading and Threaded ListModel Example.</p>
<!-- @@@WorkerScript -->
<h2>Property Documentation</h2>
<!-- $$$source -->
<div class="qmlitem"><div class="qmlproto">
<div class="table"><table class="qmlname">
<tr valign="top" class="odd" id="source-prop">
<td class="tblQmlPropNode"><p>
<a name="source-prop"></a><span class="name">source</span> : <span class="type"><a href="qml-url.html">url</a></span></p></td></tr>
</table></div>
</div><div class="qmldoc"><p>This holds the url of the JavaScript file that implements the <code>WorkerScript.onMessage()</code> handler for threaded operations.</p>
</div></div><!-- @@@source -->
<br/>
<h2>Signal Documentation</h2>
<!-- $$$message -->
<div class="qmlitem"><div class="qmlproto">
<div class="table"><table class="qmlname">
<tr valign="top" class="odd" id="message-signal">
<td class="tblQmlFuncNode"><p>
<a name="message-signal"></a><span class="name">message</span>(<span class="type">jsobject</span> <i>msg</i>)</p></td></tr>
</table></div>
</div><div class="qmldoc"><p>This signal is emitted when a message <i>msg</i> is received from a worker script in another thread through a call to <a href="qml-workerscript.html#sendMessage-method">sendMessage()</a>.</p>
<p>The corresponding handler is <code>onMessage</code>.</p>
</div></div><!-- @@@message -->
<br/>
<h2>Method Documentation</h2>
<!-- $$$sendMessage -->
<div class="qmlitem"><div class="qmlproto">
<div class="table"><table class="qmlname">
<tr valign="top" class="odd" id="sendMessage-method">
<td class="tblQmlFuncNode"><p>
<a name="sendMessage-method"></a><span class="name">sendMessage</span>(<span class="type">jsobject</span> <i>message</i>)</p></td></tr>
</table></div>
</div><div class="qmldoc"><p>Sends the given <i>message</i> to a worker script handler in another thread. The other worker script handler can receive this message through the onMessage() handler.</p>
<p>The <code>message</code> object may only contain values of the following types:</p>
<ul>
<li>boolean, number, string</li>
<li>JavaScript objects and arrays</li>
<li><a href="qml-qtqml-models-listmodel.html">ListModel</a> objects (any other type of QObject* is not allowed)</li>
</ul>
<p>All objects and arrays are copied to the <code>message</code>. With the exception of <a href="qml-qtqml-models-listmodel.html">ListModel</a> objects, any modifications by the other thread to an object passed in <code>message</code> will not be reflected in the original object.</p>
</div></div><!-- @@@sendMessage -->
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