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<a href="index.html" class="qtref"><span>Qt Reference Documentation</span></a>
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<h3><a name="toc">Contents</a></h3>
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<li class="level1"><a href="#logging">Logging</a></li>
<li class="level1"><a href="#debugging-transitions">Debugging Transitions</a></li>
<li class="level1"><a href="#debugging-module-imports">Debugging module imports</a></li>
<li class="level1"><a href="#debugging-with-qt-creator">Debugging with Qt Creator</a></li>
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<h1 class="title">Debugging QML</h1>
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<a name="logging"></a>
<h2>Logging</h2>
<p><tt>console.log</tt> can be used to print debugging information to the console. For example:</p>
<pre class="qml"> <span class="type"><a href="qml-rectangle.html">Rectangle</a></span> {
<span class="name">width</span>: <span class="number">200</span>; <span class="name">height</span>: <span class="number">200</span>
<span class="type"><a href="qml-mousearea.html">MouseArea</a></span> {
<span class="name">anchors</span>.fill: <span class="name">parent</span>
<span class="name">onClicked</span>: <span class="name">console</span>.<span class="name">log</span>(<span class="string">"clicked"</span>)
}
}</pre>
<a name="debugging-transitions"></a>
<h2>Debugging Transitions</h2>
<p>When a transition doesn't look quite right, it can be helpful to view it in slow motion to see what is happening more clearly. This functionality is supported in the <a href="qmlviewer.html">QML Viewer</a> tool: to enable this, click on the "Debugging" menu, then "Slow Down Animations".</p>
<a name="debugging-module-imports"></a>
<h2>Debugging module imports</h2>
<p>The <tt>QML_IMPORT_TRACE</tt> environment variable can be set to enable debug output from QML's import loading mechanisms.</p>
<p>For example, for a simple QML file like this:</p>
<pre class="qml"> import QtQuick 1.0
<span class="type"><a href="qml-rectangle.html">Rectangle</a></span> { <span class="name">width</span>: <span class="number">100</span>; <span class="name">height</span>: <span class="number">100</span> }</pre>
<p>If you set <tt>QML_IMPORT_TRACE=1</tt> before running the <a href="qmlviewer.html">QML Viewer</a> (or your QML C++ application), you will see output similar to this:</p>
<pre class="cpp"> <span class="type">QDeclarativeImportDatabase</span><span class="operator">::</span>addImportPath <span class="string">"/qt-sdk/imports"</span>
<span class="type">QDeclarativeImportDatabase</span><span class="operator">::</span>addImportPath <span class="string">"/qt-sdk/bin/QMLViewer.app/Contents/MacOS"</span>
<span class="type">QDeclarativeImportDatabase</span><span class="operator">::</span>addToImport <span class="number">0x106237370</span> <span class="string">"."</span> <span class="operator">-</span><span class="number">1.</span><span class="operator">-</span><span class="number">1</span> File as <span class="string">""</span>
<span class="type">QDeclarativeImportDatabase</span><span class="operator">::</span>addToImport <span class="number">0x106237370</span> <span class="string">"Qt"</span> <span class="number">4.7</span> Library as <span class="string">""</span>
<span class="type">QDeclarativeImportDatabase</span><span class="operator">::</span>resolveType <span class="string">"Rectangle"</span> <span class="operator">=</span> <span class="string">"QDeclarativeRectangle"</span></pre>
<a name="debugging-with-qt-creator"></a>
<h2>Debugging with Qt Creator</h2>
<p><a href="http://qt.nokia.com/products/developer-tools">Qt Creator</a> provides built-in support for QML debugging. QML projects and standalone C++ applications that utilize QML can be debugged on desktops as well as on remote devices. For more information, see the Qt Creator Manual.</p>
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