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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Qt Toolkit - Meta Object System</title><style type="text/css"><!--h3.fn,span.fn { margin-left: 1cm; text-indent: -1cm; }a:link { color: #004faf; text-decoration: none }a:visited { color: #672967; text-decoration: none }body { background: white; color: black; }--></style></head><body bgcolor="#ffffff"><p><table width="100%"><tr><td><a href="index.html"><img width="100" height="100" src="qtlogo.png"alt="Home" border="0"><img width="100"height="100" src="face.png" alt="Home" border="0"></a><td valign="top"><div align="right"><img src="dochead.png" width="472" height="27"><br><a href="classes.html"><b>Classes</b></a>- <a href="annotated.html">Annotated</a>- <a href="hierarchy.html">Tree</a>- <a href="functions.html">Functions</a>- <a href="index.html">Home</a>- <a href="topicals.html"><b>Structure</b> <font face="Arial,Helvetica,Geneva,Swiss,SunSans-Regular" align="center" size=32>Qte</font></a></div></table><h1 align="center"> Meta Object System</h1><br clear="all">The Meta Object System in Qt is responsible for the signal/slotmechanism for communication between objects, runtime type informationand the dynamic property system.<p>It is based on three things:<ul><li> the <a href="qobject.html">QObject</a> class,<li> the "Q_OBJECT" macro inside the private section of the classdeclaration and<li> the <a href="moc.html">Meta Object Compiler (moc)</a>. </ul><p>The <b>moc</b> reads a C++ source file. If it finds one or more classdeclarations that contain the "Q_OBJECT" macro, it produces anotherC++ source file which contains the meta object code for thisclass. This generated source file is either #included into the class'source file or compiled and linked with the class implementation.<p>Apart from the possibility to use <ahref="signalsandslots.html">signals and slots</a> for communicationbetween objects - the main reason for introducing the system - themeta object code implements certain other features in QObject:<p><ul><li> a function <a href="qobject.html#fa7716">className()</a> thatreturns the class name as string during runtime, without requiringnative runtime type information (RTTI) support through the C++compiler.<li> a function <a href="qobject.html#beb5d8">inherits()</a> thatreturns whether an object is instance of a class that inherits aspecified class within the QObject inheritance tree.<li> a function <a href="qobject.html#2418a9">tr()</a> for scoped stringtranslation as used for <a href="i18n.html"> internationalization</a>.<li> two functions <a href="qobject.html#72ec3f">setProperty()</a>and <a href="qobject.html#a110be">property()</a> to dynamically setand get <a href="properties.html">object properties</a> by name.<li> a function <a href="qobject.html#ef2243">metaObject()</a> thatreturns the associated <a href="qmetaobject.html">meta object</a> for theclass.<p></ul><p>While it is possible to use QObject as a base class without Q_OBJECTmacro and without meta object code, neither signals and slots nor theother features described here will be available. From the meta objectsystem's point of view, a QObject subclass without meta code isequivalent to its closest ancestor with meta object code. That meansfor example that className() will not return the actual name of yourclass, but the class name of this ancestor. We strongly recommend touse the macro in <em>all</em> subclasses of QObject regardless whether theyactually use signals, slots and properties or not.<p><address><hr><div align="center"><table width="100%" cellspacing="0" border="0"><tr><td>Copyright ⌨️ 快捷键说明
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