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6<title>Qt Tutorial - Chapter 2: Calling it Quits</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 2: Calling it Quits</h1>
33
34
35<p> <center><img src="t2.png" alt="Screenshot of tutorial two"></center>
36<p> Having created a window in <a href="tutorial1-01.html">Chapter 1,</a> we will
37now go on to make the application quit properly when the user tells it to.
38<p> We will also use a font that is more exciting than the default one.
39<p> <pre>/****************************************************************
40**
41** Qt tutorial 2
42**
43****************************************************************/
44
45#include &lt;<a href="qapplication-h.html">qapplication.h</a>&gt;
46#include &lt;<a href="qpushbutton-h.html">qpushbutton.h</a>&gt;
47#include &lt;<a href="qfont-h.html">qfont.h</a>&gt;
48
49
50int main( int argc, char **argv )
51{
52 <a href="qapplication.html">QApplication</a> a( argc, argv );
53
54 <a href="qpushbutton.html">QPushButton</a> quit( "Quit", 0 );
55 quit.<a href="qwidget.html#resize">resize</a>( 75, 30 );
56 quit.<a href="qwidget.html#setFont">setFont</a>( QFont( "Times", 18, QFont::Bold ) );
57
58 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>()) );
59
60 a.<a href="qapplication.html#setMainWidget">setMainWidget</a>( &amp;quit );
61 quit.<a href="qwidget.html#show">show</a>();
62 return a.<a href="qapplication.html#exec">exec</a>();
63}
64</pre>
65
66
67
68<p> <h2> Line-by-line Walkthrough
69</h2>
70<a name="1"></a><p> <pre> #include &lt;<a href="qfont-h.html">qfont.h</a>&gt;
71</pre>
72<p> Since this program uses <a href="qfont.html">QFont</a>, it needs to include qfont.h. Qt's font
73abstraction is rather different from the horror provided by X, and
74loading and using fonts has been highly optimized.
75<p> <pre> <a href="qpushbutton.html">QPushButton</a> quit( "Quit", 0 );
76</pre>
77<p> This time, the button says "Quit" and that's exactly what the program
78will do when the user clicks the button. This is not a coincidence.
79We still pass 0 as the parent, since the button is a top-level window.
80<p> <pre> <a name="x2292"></a> quit.<a href="qwidget.html#resize">resize</a>( 75, 30 );
81</pre>
82<p> We've chosen another size for the button since the text is a bit
83shorter than "Hello world!". We could also have used <a href="qfontmetrics.html">QFontMetrics</a>
84to set right size.
85<p> <pre> <a name="x2293"></a> quit.<a href="qwidget.html#setFont">setFont</a>( QFont( "Times", 18, QFont::Bold ) );
86</pre>
87<p> Here we choose a new font for the button, an 18-point bold font from
88the Times family. Note that we create the font on the spot.
89<p> It is also possible to change the default font (using <a href="qapplication.html#setFont">QApplication::setFont</a>()) for the whole application.
90<p> <pre> <a name="x2291"></a><a name="x2290"></a><a name="x2288"></a> 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>()) );
91</pre>
92<p> connect() is perhaps <em>the</em> most central feature of Qt.
93Note that connect() is a static function in <a href="qobject.html">QObject</a>. Do not confuse it
94with the connect() function in the socket library.
95<p> This line establishes a one-way connection between two Qt objects (objects
96that inherit QObject, directly or indirectly). Every Qt object can have
97both <tt>signals</tt> (to send messages) and <tt>slots</tt> (to receive messages). All
98widgets are Qt objects. They inherit <a href="qwidget.html">QWidget</a> which in turn inherits
99QObject.
100<p> Here, the <em>clicked()</em> signal of <em>quit</em> is connected to the <em>quit()</em> slot of <em>a</em>, so that when the button is clicked, the
101application quits.
102<p> The <a href="signalsandslots.html">Signals and Slots</a> documentation
103describes this topic in detail.
104<p> <h2> Behavior
105</h2>
106<a name="2"></a><p> When you run this program, you will see an even smaller window than in
107Chapter 1, filled with an even smaller button.
108<p> (See <a href="tutorial1-01.html#compiling">Compiling</a> for how to create a
109makefile and build the application.)
110<p> <h2> Exercises
111</h2>
112<a name="3"></a><p> Try to resize the window. Press the button. Oops! That connect()
113would seem to make some difference.
114<p> Are there any other signals in <a href="qpushbutton.html">QPushButton</a> you can connect to quit?
115Hint: The QPushButton inherits most of its behavior from <a href="qbutton.html">QButton</a>.
116<p> You're now ready for <a href="tutorial1-03.html">Chapter 3.</a>
117<p> [<a href="tutorial1-01.html">Previous tutorial</a>]
118[<a href="tutorial1-03.html">Next tutorial</a>]
119[<a href="tutorial.html">Main tutorial page</a>]
120<p>
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126<td align=right><div align=right>Qt 3.3.8</div>
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