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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 2: Calling it Quits</h1>
<p> <center><img src="t2.png" alt="Screenshot of tutorial two"></center>
<p> Having created a window in <a href="tutorial1-01.html">Chapter 1,</a> we will
now go on to make the application quit properly when the user tells it to.
<p> We will also use a font that is more exciting than the default one.
<p> <pre>/****************************************************************
**
** Qt tutorial 2
**
****************************************************************/
#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>>
int main( int argc, char **argv )
{
<a href="qapplication.html">QApplication</a> a( argc, argv );
<a href="qpushbutton.html">QPushButton</a> quit( "Quit", 0 );
quit.<a href="qwidget.html#resize">resize</a>( 75, 30 );
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>( &quit );
quit.<a href="qwidget.html#show">show</a>();
return a.<a href="qapplication.html#exec">exec</a>();
}
</pre>
<p> <h2> Line-by-line Walkthrough
</h2>
<a name="1"></a><p> <pre> #include <<a href="qfont-h.html">qfont.h</a>>
</pre>
<p> Since this program uses <a href="qfont.html">QFont</a>, it needs to include qfont.h. Qt's font
abstraction is rather different from the horror provided by X, and
loading and using fonts has been highly optimized.
<p> <pre> <a href="qpushbutton.html">QPushButton</a> quit( "Quit", 0 );
</pre>
<p> This time, the button says "Quit" and that's exactly what the program
will do when the user clicks the button. This is not a coincidence.
We still pass 0 as the parent, since the button is a top-level window.
<p> <pre> <a name="x2281"></a> quit.<a href="qwidget.html#resize">resize</a>( 75, 30 );
</pre>
<p> We've chosen another size for the button since the text is a bit
shorter than "Hello world!". We could also have used <a href="qfontmetrics.html">QFontMetrics</a>
to set right size.
<p> <pre> <a name="x2282"></a> quit.<a href="qwidget.html#setFont">setFont</a>( QFont( "Times", 18, QFont::Bold ) );
</pre>
<p> Here we choose a new font for the button, an 18-point bold font from
the Times family. Note that we create the font on the spot.
<p> It is also possible to change the default font (using <a href="qapplication.html#setFont">QApplication::setFont</a>()) for the whole application.
<p> <pre> <a name="x2280"></a><a name="x2279"></a><a name="x2277"></a> 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>()) );
</pre>
<p> connect() is perhaps <em>the</em> most central feature of Qt.
Note that connect() is a static function in <a href="qobject.html">QObject</a>. Do not confuse it
with the connect() function in the socket library.
<p> This line establishes a one-way connection between two Qt objects (objects
that inherit QObject, directly or indirectly). Every Qt object can have
both <tt>signals</tt> (to send messages) and <tt>slots</tt> (to receive messages). All
widgets are Qt objects. They inherit <a href="qwidget.html">QWidget</a> which in turn inherits
QObject.
<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
application quits.
<p> The <a href="signalsandslots.html">Signals and Slots</a> documentation
describes this topic in detail.
<p> <h2> Behavior
</h2>
<a name="2"></a><p> When you run this program, you will see an even smaller window than in
Chapter 1, filled with an even smaller button.
<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 to resize the window. Press the button. Oops! That connect()
would seem to make some difference.
<p> Are there any other signals in <a href="qpushbutton.html">QPushButton</a> you can connect to quit?
Hint: The QPushButton inherits most of its behavior from <a href="qbutton.html">QButton</a>.
<p> You're now ready for <a href="tutorial1-03.html">Chapter 3.</a>
<p> [<a href="tutorial1-01.html">Previous tutorial</a>]
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