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Breadcrumbs go here --> <li><a href="modules.html">Modules</a></li> <li><a href="qtdeclarative.html">QtDeclarative</a></li> <li>QDeclarativeExpression</li> </ul> </div> <div class="toolbuttons toolblock"> <ul> <li id="smallA" class="t_button">A</li> <li id="medA" class="t_button active">A</li> <li id="bigA" class="t_button">A</li> <li id="print" class="t_button"><a href="javascript:this.print();"> <span>Print</span></a></li> </ul> </div> </div> <div class="content mainContent"> <div class="toc"> <h3><a name="toc">Contents</a></h3> <ul> <li class="level1"><a href="#public-functions">Public Functions</a></li> <li class="level1"><a href="#signals">Signals</a></li> <li class="level1"><a href="#details">Detailed Description</a></li> </ul> </div> <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 <QDeclarativeExpression></span></pre><p><b>Inherits: </b><a href="qobject.html">QObject</a>.</p> <p>This class was introduced in Qt 4.7.</p> <ul> <li><a href="qdeclarativeexpression-members.html">List of all members, including inherited members</a></li> </ul> <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 & <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 & <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 & <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> </table> <ul> <li class="fn">29 public functions inherited from <a href="qobject.html#public-functions">QObject</a></li> </ul> <a name="signals"></a> <h2>Signals</h2> <table class="alignedsummary"> <tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qdeclarativeexpression.html#valueChanged">valueChanged</a></b> ()</td></tr> </table> <ul> <li class="fn">1 signal inherited from <a href="qobject.html#signals">QObject</a></li> </ul> <h3>Additional Inherited Members</h3> <ul> <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> </ul> <a name="details"></a> <!-- $$$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">"main.qml"</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">></span>rootContext()<span class="operator">,</span> myObject<span class="operator">,</span> <span class="string">"width * 2"</span>); <span class="type">int</span> result <span class="operator">=</span> expr<span class="operator">-</span><span class="operator">></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> & <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> & <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 "one off" 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> & <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 --> </div> </div> </div> </div> <div class="ft"> <span></span> </div> </div> <div class="footer"> <p> <acronym title="Copyright">©</acronym> 2015 The Qt Company Ltd. Documentation contributions included herein are the copyrights of their respective owners.</p> <br /> <p> 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.</p> <p> Documentation sources may be obtained from <a href="http://www.qt-project.org"> www.qt-project.org</a>.</p> <br /> <p> Qt and respective logos are trademarks of The Qt Company Ltd in Finland and/or other countries worldwide. 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