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<h1 class="title">QDeclarativeExpression Class Reference</h1>
<!-- $$$QDeclarativeExpression-brief -->
<p>The QDeclarativeExpression class evaluates JavaScript in a QML context. <a href="#details">More...</a></p>
<!-- @@@QDeclarativeExpression -->
<pre class="cpp"> <span class="preprocessor">#include &lt;QDeclarativeExpression&gt;</span></pre><p><b>Inherits: </b><a href="qobject.html">QObject</a>.</p>
<p>This class was introduced in Qt 4.7.</p>
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<li><a href="qdeclarativeexpression-members.html">List of all members, including inherited members</a></li>
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<a name="public-functions"></a>
<h2>Public Functions</h2>
<table class="alignedsummary">
<tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#QDeclarativeExpression">QDeclarativeExpression</a></b> ()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#QDeclarativeExpression-2">QDeclarativeExpression</a></b> ( QDeclarativeContext * <i>ctxt</i>, QObject * <i>scope</i>, const QString &amp; <i>expression</i>, QObject * <i>parent</i> = 0 )</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> virtual </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#dtor.QDeclarativeExpression">~QDeclarativeExpression</a></b> ()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#clearError">clearError</a></b> ()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QDeclarativeContext * </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#context">context</a></b> () const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QDeclarativeEngine * </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#engine">engine</a></b> () const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QDeclarativeError </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#error">error</a></b> () const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QVariant </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#evaluate">evaluate</a></b> ( bool * <i>valueIsUndefined</i> = 0 )</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QString </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#expression">expression</a></b> () const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#hasError">hasError</a></b> () const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> int </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#lineNumber">lineNumber</a></b> () const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#notifyOnValueChanged">notifyOnValueChanged</a></b> () const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QObject * </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#scopeObject">scopeObject</a></b> () const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#setExpression">setExpression</a></b> ( const QString &amp; <i>expression</i> )</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#setNotifyOnValueChanged">setNotifyOnValueChanged</a></b> ( bool <i>notifyOnChange</i> )</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#setSourceLocation">setSourceLocation</a></b> ( const QString &amp; <i>url</i>, int <i>line</i> )</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QString </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#sourceFile">sourceFile</a></b> () const</td></tr>
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<li class="fn">29 public functions inherited from <a href="qobject.html#public-functions">QObject</a></li>
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<a name="signals"></a>
<h2>Signals</h2>
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<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#valueChanged">valueChanged</a></b> ()</td></tr>
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<li class="fn">1 signal inherited from <a href="qobject.html#signals">QObject</a></li>
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<h3>Additional Inherited Members</h3>
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<li class="fn">1 property inherited from <a href="qobject.html#properties">QObject</a></li>
<li class="fn">1 public slot inherited from <a href="qobject.html#public-slots">QObject</a></li>
<li class="fn">7 static public members inherited from <a href="qobject.html#static-public-members">QObject</a></li>
<li class="fn">8 protected functions inherited from <a href="qobject.html#protected-functions">QObject</a></li>
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<!-- $$$QDeclarativeExpression-description -->
<div class="descr">
<h2>Detailed Description</h2>
<p>The QDeclarativeExpression class evaluates JavaScript in a QML context.</p>
<p>For example, given a file <tt>main.qml</tt> like this:</p>
<pre class="qml"> import QtQuick 1.0
<span class="type"><a href="qml-item.html">Item</a></span> {
<span class="name">width</span>: <span class="number">200</span>; <span class="name">height</span>: <span class="number">200</span>
}</pre>
<p>The following code evaluates a JavaScript expression in the context of the above QML:</p>
<pre class="cpp"> <span class="type"><a href="qdeclarativeengine.html">QDeclarativeEngine</a></span> <span class="operator">*</span>engine <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qdeclarativeengine.html">QDeclarativeEngine</a></span>;
<span class="type"><a href="qdeclarativecomponent.html">QDeclarativeComponent</a></span> component(engine<span class="operator">,</span> <span class="type"><a href="qurl.html">QUrl</a></span><span class="operator">::</span>fromLocalFile(<span class="string">&quot;main.qml&quot;</span>));
<span class="type"><a href="qobject.html">QObject</a></span> <span class="operator">*</span>myObject <span class="operator">=</span> component<span class="operator">.</span>create();
<span class="type">QDeclarativeExpression</span> <span class="operator">*</span>expr <span class="operator">=</span> <span class="keyword">new</span> <span class="type">QDeclarativeExpression</span>(engine<span class="operator">-</span><span class="operator">&gt;</span>rootContext()<span class="operator">,</span> myObject<span class="operator">,</span> <span class="string">&quot;width * 2&quot;</span>);
<span class="type">int</span> result <span class="operator">=</span> expr<span class="operator">-</span><span class="operator">&gt;</span><a href="qdeclarativeexpression.html#evaluate">evaluate</a>()<span class="operator">.</span>toInt(); <span class="comment">// result = 400</span></pre>
</div>
<!-- @@@QDeclarativeExpression -->
<div class="func">
<h2>Member Function Documentation</h2>
<!-- $$$QDeclarativeExpression[overload1]$$$QDeclarativeExpression -->
<h3 class="fn"><a name="QDeclarativeExpression"></a>QDeclarativeExpression::<span class="name">QDeclarativeExpression</span> ()</h3>
<p>Create an invalid <a href="qdeclarativeexpression.html">QDeclarativeExpression</a>.</p>
<p>As the expression will not have an associated <a href="qdeclarativecontext.html">QDeclarativeContext</a>, this will be a null expression object and its value will always be an invalid <a href="qvariant.html">QVariant</a>.</p>
<!-- @@@QDeclarativeExpression -->
<!-- $$$QDeclarativeExpression$$$QDeclarativeExpressionQDeclarativeContext*QObject*constQString&QObject* -->
<h3 class="fn"><a name="QDeclarativeExpression-2"></a>QDeclarativeExpression::<span class="name">QDeclarativeExpression</span> ( <span class="type"><a href="qdeclarativecontext.html">QDeclarativeContext</a></span> * <i>ctxt</i>, <span class="type"><a href="qobject.html">QObject</a></span> * <i>scope</i>, const <span class="type"><a href="qstring.html">QString</a></span> &amp; <i>expression</i>, <span class="type"><a href="qobject.html">QObject</a></span> * <i>parent</i> = 0 )</h3>
<p>Create a <a href="qdeclarativeexpression.html">QDeclarativeExpression</a> object that is a child of <i>parent</i>.</p>
<p>The <i>expression</i> JavaScript will be executed in the <i>ctxt</i> <a href="qdeclarativecontext.html">QDeclarativeContext</a>. If specified, the <i>scope</i> object's properties will also be in scope during the expression's execution.</p>
<!-- @@@QDeclarativeExpression -->
<!-- $$$~QDeclarativeExpression[overload1]$$$~QDeclarativeExpression -->
<h3 class="fn"><a name="dtor.QDeclarativeExpression"></a>QDeclarativeExpression::<span class="name">~QDeclarativeExpression</span> ()<tt> [virtual]</tt></h3>
<p>Destroy the <a href="qdeclarativeexpression.html">QDeclarativeExpression</a> instance.</p>
<!-- @@@~QDeclarativeExpression -->
<!-- $$$clearError[overload1]$$$clearError -->
<h3 class="fn"><a name="clearError"></a><span class="type">void</span> QDeclarativeExpression::<span class="name">clearError</span> ()</h3>
<p>Clear any expression errors. Calls to <a href="qdeclarativeexpression.html#hasError">hasError</a>() following this will return false.</p>
<p><b>See also </b><a href="qdeclarativeexpression.html#hasError">hasError</a>() and <a href="qdeclarativeexpression.html#error">error</a>().</p>
<!-- @@@clearError -->
<!-- $$$context[overload1]$$$context -->
<h3 class="fn"><a name="context"></a><span class="type"><a href="qdeclarativecontext.html">QDeclarativeContext</a></span> * QDeclarativeExpression::<span class="name">context</span> () const</h3>
<p>Returns the <a href="qdeclarativecontext.html">QDeclarativeContext</a> this expression is associated with, or 0 if there is no association or the <a href="qdeclarativecontext.html">QDeclarativeContext</a> has been destroyed.</p>
<!-- @@@context -->
<!-- $$$engine[overload1]$$$engine -->
<h3 class="fn"><a name="engine"></a><span class="type"><a href="qdeclarativeengine.html">QDeclarativeEngine</a></span> * QDeclarativeExpression::<span class="name">engine</span> () const</h3>
<p>Returns the <a href="qdeclarativeengine.html">QDeclarativeEngine</a> this expression is associated with, or 0 if there is no association or the <a href="qdeclarativeengine.html">QDeclarativeEngine</a> has been destroyed.</p>
<!-- @@@engine -->
<!-- $$$error[overload1]$$$error -->
<h3 class="fn"><a name="error"></a><span class="type"><a href="qdeclarativeerror.html">QDeclarativeError</a></span> QDeclarativeExpression::<span class="name">error</span> () const</h3>
<p>Return any error from the last call to <a href="qdeclarativeexpression.html#evaluate">evaluate</a>(). If there was no error, this returns an invalid <a href="qdeclarativeerror.html">QDeclarativeError</a> instance.</p>
<p><b>See also </b><a href="qdeclarativeexpression.html#hasError">hasError</a>() and <a href="qdeclarativeexpression.html#clearError">clearError</a>().</p>
<!-- @@@error -->
<!-- $$$evaluate[overload1]$$$evaluatebool* -->
<h3 class="fn"><a name="evaluate"></a><span class="type"><a href="qvariant.html">QVariant</a></span> QDeclarativeExpression::<span class="name">evaluate</span> ( <span class="type">bool</span> * <i>valueIsUndefined</i> = 0 )</h3>
<p>Evaulates the expression, returning the result of the evaluation, or an invalid <a href="qvariant.html">QVariant</a> if the expression is invalid or has an error.</p>
<p><i>valueIsUndefined</i> is set to true if the expression resulted in an undefined value.</p>
<p><b>See also </b><a href="qdeclarativeexpression.html#hasError">hasError</a>() and <a href="qdeclarativeexpression.html#error">error</a>().</p>
<!-- @@@evaluate -->
<!-- $$$expression[overload1]$$$expression -->
<h3 class="fn"><a name="expression"></a><span class="type"><a href="qstring.html">QString</a></span> QDeclarativeExpression::<span class="name">expression</span> () const</h3>
<p>Returns the expression string.</p>
<p><b>See also </b><a href="qdeclarativeexpression.html#setExpression">setExpression</a>().</p>
<!-- @@@expression -->
<!-- $$$hasError[overload1]$$$hasError -->
<h3 class="fn"><a name="hasError"></a><span class="type">bool</span> QDeclarativeExpression::<span class="name">hasError</span> () const</h3>
<p>Returns true if the last call to <a href="qdeclarativeexpression.html#evaluate">evaluate</a>() resulted in an error, otherwise false.</p>
<p><b>See also </b><a href="qdeclarativeexpression.html#error">error</a>() and <a href="qdeclarativeexpression.html#clearError">clearError</a>().</p>
<!-- @@@hasError -->
<!-- $$$lineNumber[overload1]$$$lineNumber -->
<h3 class="fn"><a name="lineNumber"></a><span class="type">int</span> QDeclarativeExpression::<span class="name">lineNumber</span> () const</h3>
<p>Returns the source file line number for this expression. The source location must have been previously set by calling <a href="qdeclarativeexpression.html#setSourceLocation">setSourceLocation</a>().</p>
<!-- @@@lineNumber -->
<!-- $$$notifyOnValueChanged[overload1]$$$notifyOnValueChanged -->
<h3 class="fn"><a name="notifyOnValueChanged"></a><span class="type">bool</span> QDeclarativeExpression::<span class="name">notifyOnValueChanged</span> () const</h3>
<p>Returns true if the <a href="qdeclarativeexpression.html#valueChanged">valueChanged</a>() signal is emitted when the expression's evaluated value changes.</p>
<p><b>See also </b><a href="qdeclarativeexpression.html#setNotifyOnValueChanged">setNotifyOnValueChanged</a>().</p>
<!-- @@@notifyOnValueChanged -->
<!-- $$$scopeObject[overload1]$$$scopeObject -->
<h3 class="fn"><a name="scopeObject"></a><span class="type"><a href="qobject.html">QObject</a></span> * QDeclarativeExpression::<span class="name">scopeObject</span> () const</h3>
<p>Returns the expression's scope object, if provided, otherwise 0.</p>
<p>In addition to data provided by the expression's <a href="qdeclarativecontext.html">QDeclarativeContext</a>, the scope object's properties are also in scope during the expression's evaluation.</p>
<!-- @@@scopeObject -->
<!-- $$$setExpression[overload1]$$$setExpressionconstQString& -->
<h3 class="fn"><a name="setExpression"></a><span class="type">void</span> QDeclarativeExpression::<span class="name">setExpression</span> ( const <span class="type"><a href="qstring.html">QString</a></span> &amp; <i>expression</i> )</h3>
<p>Set the expression to <i>expression</i>.</p>
<p><b>See also </b><a href="qdeclarativeexpression.html#expression">expression</a>().</p>
<!-- @@@setExpression -->
<!-- $$$setNotifyOnValueChanged[overload1]$$$setNotifyOnValueChangedbool -->
<h3 class="fn"><a name="setNotifyOnValueChanged"></a><span class="type">void</span> QDeclarativeExpression::<span class="name">setNotifyOnValueChanged</span> ( <span class="type">bool</span> <i>notifyOnChange</i> )</h3>
<p>Sets whether the <a href="qdeclarativeexpression.html#valueChanged">valueChanged</a>() signal is emitted when the expression's evaluated value changes.</p>
<p>If <i>notifyOnChange</i> is true, the <a href="qdeclarativeexpression.html">QDeclarativeExpression</a> will monitor properties involved in the expression's evaluation, and emit <a href="qdeclarativeexpression.html#valueChanged">QDeclarativeExpression::valueChanged</a>() if they have changed. This allows an application to ensure that any value associated with the result of the expression remains up to date.</p>
<p>If <i>notifyOnChange</i> is false (default), the <a href="qdeclarativeexpression.html">QDeclarativeExpression</a> will not montitor properties involved in the expression's evaluation, and <a href="qdeclarativeexpression.html#valueChanged">QDeclarativeExpression::valueChanged</a>() will never be emitted. This is more efficient if an application wants a &quot;one off&quot; evaluation of the expression.</p>
<p><b>See also </b><a href="qdeclarativeexpression.html#notifyOnValueChanged">notifyOnValueChanged</a>().</p>
<!-- @@@setNotifyOnValueChanged -->
<!-- $$$setSourceLocation[overload1]$$$setSourceLocationconstQString&int -->
<h3 class="fn"><a name="setSourceLocation"></a><span class="type">void</span> QDeclarativeExpression::<span class="name">setSourceLocation</span> ( const <span class="type"><a href="qstring.html">QString</a></span> &amp; <i>url</i>, <span class="type">int</span> <i>line</i> )</h3>
<p>Set the location of this expression to <i>line</i> of <i>url</i>. This information is used by the script engine.</p>
<!-- @@@setSourceLocation -->
<!-- $$$sourceFile[overload1]$$$sourceFile -->
<h3 class="fn"><a name="sourceFile"></a><span class="type"><a href="qstring.html">QString</a></span> QDeclarativeExpression::<span class="name">sourceFile</span> () const</h3>
<p>Returns the source file URL for this expression. The source location must have been previously set by calling <a href="qdeclarativeexpression.html#setSourceLocation">setSourceLocation</a>().</p>
<!-- @@@sourceFile -->
<!-- $$$valueChanged[overload1]$$$valueChanged -->
<h3 class="fn"><a name="valueChanged"></a><span class="type">void</span> QDeclarativeExpression::<span class="name">valueChanged</span> ()<tt> [signal]</tt></h3>
<p>Emitted each time the expression value changes from the last time it was evaluated. The expression must have been evaluated at least once (by calling <a href="qdeclarativeexpression.html#evaluate">QDeclarativeExpression::evaluate</a>()) before this signal will be emitted.</p>
<!-- @@@valueChanged -->
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