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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 - Object Trees and Object Ownership</title><style type="text/css"><!--
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<h1 align=center> Object Trees and Object Ownership</h1><br clear="all">
<a href="qobject.html">QObjects</a> organize themselves in object trees.
When you create a QObject with another object as parent, it's added to
the parent's <a href="qobject.html#f790ce">children()</a> list, and
is deleted when the parent is. This turns out to fit the needs of GUI
objects well. For example, a <a href="qaccel.html">QAccel</a> (keyboard accelerator) is a
child of the right window, so when the user closes that window, the
accelerator is deleted too.
<p>
The static function <a href="qobject.html#3cb047">QObject::objectTrees()</a> gives you access to all
the root objects that currently exist.
<p>
<a href="qwidget.html">QWidget</a>, the base class of everything that shows up on the screen,
extends the parent/child relationship: a child normally also becomes a
so-called child widget, i.e. it is displayed in its parent's
coordinate system and is graphically clipped by its parent's
boundaries. Thus, when the the application deletes a message box
after it's been closed, the message box' OK button is deleted too,
just the way you would want, because the button is a child of the
message box.
<p>
Of course, you can also delete a child object yourself, and it will
remove itself from its parent. For example, when the user removes a
toolbar that could often result in the application deleting one of the
<a href="qtoolbar.html">QToolBar</a> objects, and the tool bar's <a href="qmainwindow.html">QMainWindow</a> parent would
then notice the change and reconfigure its screen space.
<p>
The debugging functions <a href="qobject.html#c21cea">QObject::dumpObjectTree()</a> and <a href="qobject.html#d459b3">QObject::dumpObjectInfo()</a> are often useful when an application looks or
acts strangely.
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<td>Copyright 2001 Trolltech<td><a href="http://www.trolltech.com/trademarks.html">Trademarks</a>
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