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6<title>Qt Tutorial - Chapter 3: Family Values</title>
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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>Qt Tutorial - Chapter 3: Family Values</h1>
33
34
35<p> <center><img src="t3.png" alt="Screenshot of tutorial three"></center>
36<p> This example shows how to create parent and child widgets.
37<p> We'll keep it simple and use just a single parent and a lone child.
38<p> <pre>/****************************************************************
39**
40** Qt tutorial 3
41**
42****************************************************************/
43
44#include &lt;<a href="qapplication-h.html">qapplication.h</a>&gt;
45#include &lt;<a href="qpushbutton-h.html">qpushbutton.h</a>&gt;
46#include &lt;<a href="qfont-h.html">qfont.h</a>&gt;
47#include &lt;<a href="qvbox-h.html">qvbox.h</a>&gt;
48
49int main( int argc, char **argv )
50{
51 <a href="qapplication.html">QApplication</a> a( argc, argv );
52
53 <a href="qvbox.html">QVBox</a> box;
54 box.<a href="qwidget.html#resize">resize</a>( 200, 120 );
55
56 <a href="qpushbutton.html">QPushButton</a> quit( "Quit", &amp;box );
57 quit.<a href="qwidget.html#setFont">setFont</a>( QFont( "Times", 18, QFont::Bold ) );
58
59 QObject::<a href="qobject.html#connect">connect</a>( &amp;quit, SIGNAL(<a href="qbutton.html#clicked">clicked</a>()), &amp;a, SLOT(<a href="qapplication.html#quit">quit</a>()) );
60
61 a.<a href="qapplication.html#setMainWidget">setMainWidget</a>( &amp;box );
62 box.<a href="qwidget.html#show">show</a>();
63
64 return a.<a href="qapplication.html#exec">exec</a>();
65}
66</pre>
67
68
69
70<p> <h2> Line-by-line Walkthrough
71</h2>
72<a name="1"></a><p> <pre> #include &lt;<a href="qvbox-h.html">qvbox.h</a>&gt;
73</pre>
74<p> We add an include of qvbox.h to get the layout class we'll use.
75<p> <pre> <a href="qvbox.html">QVBox</a> box;
76</pre>
77<p> Here we simply create a vertical box container. The <a href="qvbox.html">QVBox</a> arranges
78its child widgets in a vertical row, one above the other, handing out
79space according to each child's <a href="qwidget.html#sizePolicy">QWidget::sizePolicy</a>().
80<p> <pre> <a name="x2300"></a> box.<a href="qwidget.html#resize">resize</a>( 200, 120 );
81</pre>
82<p> We set its width to 200 pixels and the height to 120 pixels.
83<p> <pre> <a href="qpushbutton.html">QPushButton</a> quit( "Quit", &amp;box );
84</pre>
85<p> A child is born.
86<p> This <a href="qpushbutton.html">QPushButton</a> is created with both a text ("Quit") and a parent
87(box). A child widget is always on top of its parent. When
88displayed, it is clipped by its parent's bounds.
89<p> The parent widget, the QVBox, automatically adds the child centered in
90its box. Because nothing else is added, the button gets all the space
91the parent has.
92<p> <pre> <a name="x2302"></a> box.<a href="qwidget.html#show">show</a>();
93</pre>
94<p> When a parent widget is shown, it will call show for all its children
95(except those on which you have done an explicit <a href="qwidget.html#hide">QWidget::hide</a>()).
96<p> <h2> Behavior
97</h2>
98<a name="2"></a><p> The button no longer fills the entire widget. Instead, it gets a
99"natural" size. This is because there is now a new top-level widget,
100which uses the button's size hint and size change policy to set the
101button'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.)
102<p> (See <a href="tutorial1-01.html#compiling">Compiling</a> for how to create a
103makefile and build the application.)
104<p> <h2> Exercises
105</h2>
106<a name="3"></a><p> Try resizing the window. How does the button change? What is the
107button's size-change policy? What happens to the button's height if
108you run the program with a bigger font? What happens if you try to
109make the window <em>really</em> small?
110<p> You're now ready for <a href="tutorial1-04.html">Chapter 4.</a>
111<p> [<a href="tutorial1-02.html">Previous tutorial</a>]
112[<a href="tutorial1-04.html">Next tutorial</a>]
113[<a href="tutorial.html">Main tutorial page</a>]
114<p>
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118<td>Copyright &copy; 2007
119<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
120<td align=right><div align=right>Qt 3.3.8</div>
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