| [190] | 1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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| 2 | <!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/tutorial.doc:216 -->
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| 6 | <title>Qt Tutorial - Chapter 2: Calling it Quits</title>
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| 18 | <td valign=center>
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| 20 | <font color="#004faf">Home</font></a>
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| 22 | <font color="#004faf">All Classes</font></a>
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| 24 | <font color="#004faf">Main Classes</font></a>
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| 30 | <font color="#004faf">Functions</font></a>
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| 31 | </td>
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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>
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| 33 |
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| 34 |
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| 35 | <p> <center><img src="t2.png" alt="Screenshot of tutorial two"></center>
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| 36 | <p> Having created a window in <a href="tutorial1-01.html">Chapter 1,</a> we will
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| 37 | now go on to make the application quit properly when the user tells it to.
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| 38 | <p> We will also use a font that is more exciting than the default one.
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| 39 | <p> <pre>/****************************************************************
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| 40 | **
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| 41 | ** Qt tutorial 2
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| 42 | **
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| 43 | ****************************************************************/
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| 44 |
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| 45 | #include <<a href="qapplication-h.html">qapplication.h</a>>
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| 46 | #include <<a href="qpushbutton-h.html">qpushbutton.h</a>>
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| 47 | #include <<a href="qfont-h.html">qfont.h</a>>
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| 48 |
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| 49 |
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| 50 | int main( int argc, char **argv )
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| 51 | {
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| 52 | <a href="qapplication.html">QApplication</a> a( argc, argv );
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| 53 |
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| 54 | <a href="qpushbutton.html">QPushButton</a> quit( "Quit", 0 );
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| 55 | quit.<a href="qwidget.html#resize">resize</a>( 75, 30 );
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| 56 | quit.<a href="qwidget.html#setFont">setFont</a>( QFont( "Times", 18, QFont::Bold ) );
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| 57 |
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| 58 | 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>()) );
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| 59 |
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| 60 | a.<a href="qapplication.html#setMainWidget">setMainWidget</a>( &quit );
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| 61 | quit.<a href="qwidget.html#show">show</a>();
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| 62 | return a.<a href="qapplication.html#exec">exec</a>();
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| 63 | }
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| 64 | </pre>
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| 65 |
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| 66 |
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| 67 |
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| 68 | <p> <h2> Line-by-line Walkthrough
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| 69 | </h2>
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| 70 | <a name="1"></a><p> <pre> #include <<a href="qfont-h.html">qfont.h</a>>
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| 71 | </pre>
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| 72 | <p> Since this program uses <a href="qfont.html">QFont</a>, it needs to include qfont.h. Qt's font
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| 73 | abstraction is rather different from the horror provided by X, and
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| 74 | loading and using fonts has been highly optimized.
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| 75 | <p> <pre> <a href="qpushbutton.html">QPushButton</a> quit( "Quit", 0 );
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| 76 | </pre>
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| 77 | <p> This time, the button says "Quit" and that's exactly what the program
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| 78 | will do when the user clicks the button. This is not a coincidence.
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| 79 | We still pass 0 as the parent, since the button is a top-level window.
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| 80 | <p> <pre> <a name="x2292"></a> quit.<a href="qwidget.html#resize">resize</a>( 75, 30 );
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| 81 | </pre>
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| 82 | <p> We've chosen another size for the button since the text is a bit
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| 83 | shorter than "Hello world!". We could also have used <a href="qfontmetrics.html">QFontMetrics</a>
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| 84 | to set right size.
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| 85 | <p> <pre> <a name="x2293"></a> quit.<a href="qwidget.html#setFont">setFont</a>( QFont( "Times", 18, QFont::Bold ) );
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| 86 | </pre>
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| 87 | <p> Here we choose a new font for the button, an 18-point bold font from
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| 88 | the Times family. Note that we create the font on the spot.
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| 89 | <p> It is also possible to change the default font (using <a href="qapplication.html#setFont">QApplication::setFont</a>()) for the whole application.
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| 90 | <p> <pre> <a name="x2291"></a><a name="x2290"></a><a name="x2288"></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>()) );
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| 91 | </pre>
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| 92 | <p> connect() is perhaps <em>the</em> most central feature of Qt.
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| 93 | Note that connect() is a static function in <a href="qobject.html">QObject</a>. Do not confuse it
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| 94 | with the connect() function in the socket library.
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| 95 | <p> This line establishes a one-way connection between two Qt objects (objects
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| 96 | that inherit QObject, directly or indirectly). Every Qt object can have
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| 97 | both <tt>signals</tt> (to send messages) and <tt>slots</tt> (to receive messages). All
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| 98 | widgets are Qt objects. They inherit <a href="qwidget.html">QWidget</a> which in turn inherits
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| 99 | QObject.
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| 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
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| 101 | application quits.
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| 102 | <p> The <a href="signalsandslots.html">Signals and Slots</a> documentation
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| 103 | describes this topic in detail.
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| 104 | <p> <h2> Behavior
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| 105 | </h2>
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| 106 | <a name="2"></a><p> When you run this program, you will see an even smaller window than in
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| 107 | Chapter 1, filled with an even smaller button.
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| 108 | <p> (See <a href="tutorial1-01.html#compiling">Compiling</a> for how to create a
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| 109 | makefile and build the application.)
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| 110 | <p> <h2> Exercises
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| 111 | </h2>
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| 112 | <a name="3"></a><p> Try to resize the window. Press the button. Oops! That connect()
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| 113 | would seem to make some difference.
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| 114 | <p> Are there any other signals in <a href="qpushbutton.html">QPushButton</a> you can connect to quit?
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| 115 | Hint: The QPushButton inherits most of its behavior from <a href="qbutton.html">QButton</a>.
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| 116 | <p> You're now ready for <a href="tutorial1-03.html">Chapter 3.</a>
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| 117 | <p> [<a href="tutorial1-01.html">Previous tutorial</a>]
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| 118 | [<a href="tutorial1-03.html">Next tutorial</a>]
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| 119 | [<a href="tutorial.html">Main tutorial page</a>]
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| 120 | <p>
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| 122 | <p><address><hr><div align=center>
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| 123 | <table width=100% cellspacing=0 border=0><tr>
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| 124 | <td>Copyright © 2007
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| 125 | <a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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| 126 | <td align=right><div align=right>Qt 3.3.8</div>
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| 127 | </table></div></address></body>
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| 128 | </html>
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