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| 31 | </td>
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| 32 | <td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>Meta Object System</h1>
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| 33 |
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| 34 |
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| 35 |
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| 36 | <p> <!-- index meta object --><a name="meta-object"></a><!-- index Q_OBJECT --><a name="Q_OBJECT"></a>
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| 37 | <p> Qt's Meta Object System provides the signals and slots mechanism for
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| 38 | inter-object communication, runtime type information, and the dynamic
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| 39 | property system.
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| 40 | <p> The Meta Object System is based on three things:
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| 41 | <ol type=1>
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| 42 | <li> the <a href="qobject.html">QObject</a> class;
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| 43 | <li> the Q_OBJECT macro inside the private section of the class
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| 44 | declaration;
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| 45 | <li> the <a href="moc.html">Meta Object Compiler (moc)</a>.
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| 46 | </ol>
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| 47 | <p> The <em><a href="moc.html#moc">moc</a></em> reads a C++ source file. If it finds one or more class
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| 48 | declarations that contain the Q_OBJECT macro, it produces another C++
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| 49 | source file which contains the meta object code for the classes that
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| 50 | contain the Q_OBJECT macro. This generated source file is either
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| 51 | #included into the class's source file or compiled and linked with the
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| 52 | class's implementation.
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| 53 | <p> In addition to providing the <a href="signalsandslots.html">signals and
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| 54 | slots</a> mechanism for communication between objects (the main
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| 55 | reason for introducing the system), the meta object code provides
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| 56 | additional features in QObject:
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| 57 | <p> <ul>
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| 58 | <p> <li> the <a href="qobject.html#className">className()</a> function that
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| 59 | returns the class name as a string at runtime, without requiring
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| 60 | native runtime type information (RTTI) support through the C++
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| 61 | compiler.
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| 62 | <p> <li> the <a href="qobject.html#inherits">inherits()</a> function that
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| 63 | returns whether an object is an instance of a class that inherits a
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| 64 | specified class within the <a href="qobject.html">QObject</a> inheritance tree.
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| 65 | <p> <li> the <a href="qobject.html#tr">tr()</a> and
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| 66 | <a href="qobject.html#trUtf8">trUtf8()</a> functions for string
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| 67 | translation as used for <a href="i18n.html#internationalization">internationalization</a>.
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| 68 | <p> <li> the <a href="qobject.html#setProperty">setProperty()</a> and <a href="qobject.html#property">property()</a> functions for dynamically
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| 69 | setting and getting <a href="properties.html">object properties</a> by
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| 70 | name.
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| 71 | <p> <li> the <a href="qobject.html#metaObject">metaObject()</a> function that
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| 72 | returns the associated <a href="qmetaobject.html">meta object</a> for the
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| 73 | class.
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| 74 | <p> </ul>
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| 75 | <p> While it is possible to use QObject as a base class without the
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| 76 | Q_OBJECT macro and without meta object code, neither signals and slots
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| 77 | nor the other features described here will be available if the
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| 78 | Q_OBJECT macro is not used. From the meta object system's point of
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| 79 | view, a QObject subclass without meta code is equivalent to its
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| 80 | closest ancestor with meta object code. This means for example, that
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| 81 | className() will not return the actual name of your class, but the
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| 82 | class name of this ancestor. We <em>strongly</em> recommend that all
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| 83 | subclasses of <a href="qobject.html">QObject</a> use the Q_OBJECT macro regardless of whether
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| 84 | they actually use signals, slots and properties or not.
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| 85 | <p>
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| 86 | <!-- eof -->
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| 87 | <p><address><hr><div align=center>
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| 88 | <table width=100% cellspacing=0 border=0><tr>
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| 89 | <td>Copyright © 2007
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| 90 | <a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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| 91 | <td align=right><div align=right>Qt 3.3.8</div>
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| 92 | </table></div></address></body>
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| 93 | </html>
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