<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <!-- /home/reggie/tmp/qt-3.1-reggie-23625/qt-x11-free-3.1.1/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"><!-- h3.fn,span.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 Classes</font></a> | <a href="mainclasses.html"> <font color="#004faf">Main Classes</font></a> | <a href="annotated.html"> <font color="#004faf">Annotated</font></a> | <a href="groups.html"> <font color="#004faf">Grouped 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 <<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="x2223"></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="x2224"></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="x2222"></a><a name="x2221"></a><a name="x2219"></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>] [<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 © 2002 <a href="http://www.trolltech.com">Trolltech</a><td><a href="http://www.trolltech.com/trademarks.html">Trademarks</a> <td align=right><div align=right>Qt version 3.1.1</div> </table></div></address></body> </html>