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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>Qt Tutorial - Chapter 3: Family Values</h1>
<p> <center><img src="t3.png" alt="Screenshot of tutorial three"></center>
<p> This example shows how to create parent and child widgets.
<p> We'll keep it simple and use just a single parent and a lone child.
<p> <pre>/****************************************************************
**
** Qt tutorial 3
**
****************************************************************/
#include <<a href="qapplication-h.html">qapplication.h</a>>
#include <<a href="qpushbutton-h.html">qpushbutton.h</a>>
#include <<a href="qfont-h.html">qfont.h</a>>
#include <<a href="qvbox-h.html">qvbox.h</a>>
int main( int argc, char **argv )
{
<a href="qapplication.html">QApplication</a> a( argc, argv );
<a href="qvbox.html">QVBox</a> box;
box.<a href="qwidget.html#resize">resize</a>( 200, 120 );
<a href="qpushbutton.html">QPushButton</a> quit( "Quit", &box );
quit.<a href="qwidget.html#setFont">setFont</a>( QFont( "Times", 18, QFont::Bold ) );
QObject::<a href="qobject.html#connect">connect</a>( &quit, SIGNAL(<a href="qbutton.html#clicked">clicked</a>()), &a, SLOT(<a href="qapplication.html#quit">quit</a>()) );
a.<a href="qapplication.html#setMainWidget">setMainWidget</a>( &box );
box.<a href="qwidget.html#show">show</a>();
return a.<a href="qapplication.html#exec">exec</a>();
}
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<p> <h2> Line-by-line Walkthrough
</h2>
<a name="1"></a><p> <pre> #include <<a href="qvbox-h.html">qvbox.h</a>>
</pre>
<p> We add an include of qvbox.h to get the layout class we'll use.
<p> <pre> <a href="qvbox.html">QVBox</a> box;
</pre>
<p> Here we simply create a vertical box container. The <a href="qvbox.html">QVBox</a> arranges
its child widgets in a vertical row, one above the other, handing out
space according to each child's <a href="qwidget.html#sizePolicy">QWidget::sizePolicy</a>().
<p> <pre> <a name="x2300"></a> box.<a href="qwidget.html#resize">resize</a>( 200, 120 );
</pre>
<p> We set its width to 200 pixels and the height to 120 pixels.
<p> <pre> <a href="qpushbutton.html">QPushButton</a> quit( "Quit", &box );
</pre>
<p> A child is born.
<p> This <a href="qpushbutton.html">QPushButton</a> is created with both a text ("Quit") and a parent
(box). A child widget is always on top of its parent. When
displayed, it is clipped by its parent's bounds.
<p> The parent widget, the QVBox, automatically adds the child centered in
its box. Because nothing else is added, the button gets all the space
the parent has.
<p> <pre> <a name="x2302"></a> box.<a href="qwidget.html#show">show</a>();
</pre>
<p> When a parent widget is shown, it will call show for all its children
(except those on which you have done an explicit <a href="qwidget.html#hide">QWidget::hide</a>()).
<p> <h2> Behavior
</h2>
<a name="2"></a><p> The button no longer fills the entire widget. Instead, it gets a
"natural" size. This is because there is now a new top-level widget,
which uses the button's size hint and size change policy to set the
button's size and position. (See <a href="qwidget.html#sizeHint">QWidget::sizeHint</a>() and <a href="qwidget.html#setSizePolicy">QWidget::setSizePolicy</a>() for more information about these functions.)
<p> (See <a href="tutorial1-01.html#compiling">Compiling</a> for how to create a
makefile and build the application.)
<p> <h2> Exercises
</h2>
<a name="3"></a><p> Try resizing the window. How does the button change? What is the
button's size-change policy? What happens to the button's height if
you run the program with a bigger font? What happens if you try to
make the window <em>really</em> small?
<p> You're now ready for <a href="tutorial1-04.html">Chapter 4.</a>
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