You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
qt3/doc/html/tutorial1-02.html

129 lines
6.1 KiB

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/tutorial.doc:216 -->
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Qt Tutorial - Chapter 2: Calling it Quits</title>
<style type="text/css"><!--
fn { margin-left: 1cm; text-indent: -1cm; }
a:link { color: #004faf; text-decoration: none }
a:visited { color: #672967; text-decoration: none }
body { background: #ffffff; color: black; }
--></style>
</head>
<body>
<table border="0" cellpadding="0" cellspacing="0" width="100%">
<tr bgcolor="#E5E5E5">
<td valign=center>
<a href="index.html">
<font color="#004faf">Home</font></a>
| <a href="classes.html">
<font color="#004faf">All&nbsp;Classes</font></a>
| <a href="mainclasses.html">
<font color="#004faf">Main&nbsp;Classes</font></a>
| <a href="annotated.html">
<font color="#004faf">Annotated</font></a>
| <a href="groups.html">
<font color="#004faf">Grouped&nbsp;Classes</font></a>
| <a href="functions.html">
<font color="#004faf">Functions</font></a>
</td>
<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 &lt;<a href="qapplication-h.html">qapplication.h</a>&gt;
#include &lt;<a href="qpushbutton-h.html">qpushbutton.h</a>&gt;
#include &lt;<a href="qfont-h.html">qfont.h</a>&gt;
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>( &amp;quit, SIGNAL(<a href="qbutton.html#clicked">clicked</a>()), &amp;a, SLOT(<a href="qapplication.html#quit">quit</a>()) );
a.<a href="qapplication.html#setMainWidget">setMainWidget</a>( &amp;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 &lt;<a href="qfont-h.html">qfont.h</a>&gt;
</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="x2292"></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="x2293"></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="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>()) );
</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>]
[<a href="tutorial1-03.html">Next tutorial</a>]
[<a href="tutorial.html">Main tutorial page</a>]
<p>
<!-- eof -->
<p><address><hr><div align=center>
<table width=100% cellspacing=0 border=0><tr>
<td>Copyright &copy; 2007
<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
<td align=right><div align=right>Qt 3.3.8</div>
</table></div></address></body>
</html>