<?xml version="1.0" encoding="iso-8859-1"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "DTD/xhtml1-strict.dtd"> <html><head><title>QDeclarativeExpression Class Reference</title><style>h3.fn,span.fn { margin-left: 1cm; text-indent: -1cm } a:link { color: #004faf; text-decoration: none } a:visited { color: #672967; text-decoration: none } td.postheader { font-family: sans-serif } tr.address { font-family: sans-serif } body { background: #ffffff; color: black; } </style></head><body><table border="0" cellpadding="0" cellspacing="0" width="100%"><tr /><td align="left" valign="top" width="32"><img align="left" border="0" height="32" src="images/rb-logo.png" width="32" /></td><td width="1">  </td><td class="postheader" valign="center"><a href="index.html"><font color="#004faf">Home</font></a> · <a href="classes.html"><font color="#004faf">All Classes</font></a> · <a href="modules.html"><font color="#004faf">Modules</font></a></td></table><h1 align="center">QDeclarativeExpression Class Reference<br /><sup><sup>[<a href="qtdeclarative.html">QtDeclarative</a> module]</sup></sup></h1><p>The QDeclarativeExpression class evaluates JavaScript in a QML context. <a href="#details">More...</a></p> <p>Inherits <a href="qobject.html">QObject</a>.</p><h3>Methods</h3><ul><li><div class="fn" /><b><a href="qdeclarativeexpression.html#QDeclarativeExpression">__init__</a></b> (<i>self</i>)</li><li><div class="fn" /><b><a href="qdeclarativeexpression.html#QDeclarativeExpression-2">__init__</a></b> (<i>self</i>, QDeclarativeContext, QObject, QString, QObject <i>parent</i> = None)</li><li><div class="fn" /><b><a href="qdeclarativeexpression.html#clearError">clearError</a></b> (<i>self</i>)</li><li><div class="fn" />QDeclarativeContext <b><a href="qdeclarativeexpression.html#context">context</a></b> (<i>self</i>)</li><li><div class="fn" />QDeclarativeEngine <b><a href="qdeclarativeexpression.html#engine">engine</a></b> (<i>self</i>)</li><li><div class="fn" />QDeclarativeError <b><a href="qdeclarativeexpression.html#error">error</a></b> (<i>self</i>)</li><li><div class="fn" />(QVariant, bool <i>valueIsUndefined</i>) <b><a href="qdeclarativeexpression.html#evaluate">evaluate</a></b> (<i>self</i>)</li><li><div class="fn" />QString <b><a href="qdeclarativeexpression.html#expression">expression</a></b> (<i>self</i>)</li><li><div class="fn" />bool <b><a href="qdeclarativeexpression.html#hasError">hasError</a></b> (<i>self</i>)</li><li><div class="fn" />int <b><a href="qdeclarativeexpression.html#lineNumber">lineNumber</a></b> (<i>self</i>)</li><li><div class="fn" />bool <b><a href="qdeclarativeexpression.html#notifyOnValueChanged">notifyOnValueChanged</a></b> (<i>self</i>)</li><li><div class="fn" />QObject <b><a href="qdeclarativeexpression.html#scopeObject">scopeObject</a></b> (<i>self</i>)</li><li><div class="fn" /><b><a href="qdeclarativeexpression.html#setExpression">setExpression</a></b> (<i>self</i>, QString)</li><li><div class="fn" /><b><a href="qdeclarativeexpression.html#setNotifyOnValueChanged">setNotifyOnValueChanged</a></b> (<i>self</i>, bool)</li><li><div class="fn" /><b><a href="qdeclarativeexpression.html#setSourceLocation">setSourceLocation</a></b> (<i>self</i>, QString <i>fileName</i>, int <i>line</i>)</li><li><div class="fn" />QString <b><a href="qdeclarativeexpression.html#sourceFile">sourceFile</a></b> (<i>self</i>)</li></ul><h3>Qt Signals</h3><ul><li><div class="fn" />void <b><a href="qdeclarativeexpression.html#valueChanged">valueChanged</a></b> ()</li></ul><a name="details" /><hr /><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><hr /><h2>Method Documentation</h2><h3 class="fn"><a name="QDeclarativeExpression" />QDeclarativeExpression.__init__ (<i>self</i>)</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> <h3 class="fn"><a name="QDeclarativeExpression-2" />QDeclarativeExpression.__init__ (<i>self</i>, <a href="qdeclarativecontext.html">QDeclarativeContext</a>, <a href="qobject.html">QObject</a>, QString, <a href="qobject.html">QObject</a> <i>parent</i> = None)</h3><p>The <i>parent</i> argument, if not None, causes <i>self</i> to be owned by Qt instead of PyQt.</p><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> <h3 class="fn"><a name="clearError" />QDeclarativeExpression.clearError (<i>self</i>)</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> <h3 class="fn"><a name="context" /><a href="qdeclarativecontext.html">QDeclarativeContext</a> QDeclarativeExpression.context (<i>self</i>)</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> <h3 class="fn"><a name="engine" /><a href="qdeclarativeengine.html">QDeclarativeEngine</a> QDeclarativeExpression.engine (<i>self</i>)</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> <h3 class="fn"><a name="error" /><a href="qdeclarativeerror.html">QDeclarativeError</a> QDeclarativeExpression.error (<i>self</i>)</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> <h3 class="fn"><a name="evaluate" />(QVariant, bool <i>valueIsUndefined</i>) QDeclarativeExpression.evaluate (<i>self</i>)</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> <h3 class="fn"><a name="expression" />QString QDeclarativeExpression.expression (<i>self</i>)</h3><p>Returns the expression string.</p> <p><b>See also</b> <a href="qdeclarativeexpression.html#setExpression">setExpression</a>().</p> <h3 class="fn"><a name="hasError" />bool QDeclarativeExpression.hasError (<i>self</i>)</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> <h3 class="fn"><a name="lineNumber" />int QDeclarativeExpression.lineNumber (<i>self</i>)</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> <h3 class="fn"><a name="notifyOnValueChanged" />bool QDeclarativeExpression.notifyOnValueChanged (<i>self</i>)</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> <h3 class="fn"><a name="scopeObject" /><a href="qobject.html">QObject</a> QDeclarativeExpression.scopeObject (<i>self</i>)</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> <h3 class="fn"><a name="setExpression" />QDeclarativeExpression.setExpression (<i>self</i>, QString)</h3><p>Set the expression to <i>expression</i>.</p> <p><b>See also</b> <a href="qdeclarativeexpression.html#expression">expression</a>().</p> <h3 class="fn"><a name="setNotifyOnValueChanged" />QDeclarativeExpression.setNotifyOnValueChanged (<i>self</i>, bool)</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> <h3 class="fn"><a name="setSourceLocation" />QDeclarativeExpression.setSourceLocation (<i>self</i>, QString <i>fileName</i>, int <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> <h3 class="fn"><a name="sourceFile" />QString QDeclarativeExpression.sourceFile (<i>self</i>)</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> <hr /><h2>Qt Signal Documentation</h2><h3 class="fn"><a name="valueChanged" />void valueChanged ()</h3><p>This is the default overload of this signal.</p><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> <address><hr /><div align="center"><table border="0" cellspacing="0" width="100%"><tr class="address"><td align="left" width="25%">PyQt 4.10.3 for X11</td><td align="center" width="50%">Copyright © <a href="http://www.riverbankcomputing.com">Riverbank Computing Ltd</a> and <a href="http://www.qtsoftware.com">Nokia</a> 2012</td><td align="right" width="25%">Qt 4.8.5</td></tr></table></div></address></body></html>