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169 lines
8.0 KiB
169 lines
8.0 KiB
14 years ago
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/tutorial.doc:487 -->
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>Qt Tutorial - Chapter 5: Building Blocks</title>
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<style type="text/css"><!--
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fn { margin-left: 1cm; text-indent: -1cm; }
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a:link { color: #004faf; text-decoration: none }
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a:visited { color: #672967; text-decoration: none }
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body { background: #ffffff; color: black; }
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--></style>
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</head>
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<body>
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<table border="0" cellpadding="0" cellspacing="0" width="100%">
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<tr bgcolor="#E5E5E5">
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<td valign=center>
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<a href="index.html">
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<font color="#004faf">Home</font></a>
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| <a href="classes.html">
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<font color="#004faf">All Classes</font></a>
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| <a href="mainclasses.html">
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<font color="#004faf">Main Classes</font></a>
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| <a href="annotated.html">
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<font color="#004faf">Annotated</font></a>
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<font color="#004faf">Grouped Classes</font></a>
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| <a href="functions.html">
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<font color="#004faf">Functions</font></a>
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</td>
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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 5: Building Blocks</h1>
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<p> <center><img src="t5.png" alt="Screenshot of tutorial five"></center>
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<p> This example shows how to create and connect together several widgets
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by using signals and slots, and how to handle resize events.
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<p> <pre>/****************************************************************
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**
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** Qt tutorial 5
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**
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****************************************************************/
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#include <<a href="qapplication-h.html">qapplication.h</a>>
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#include <<a href="qpushbutton-h.html">qpushbutton.h</a>>
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#include <<a href="qslider-h.html">qslider.h</a>>
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#include <<a href="qlcdnumber-h.html">qlcdnumber.h</a>>
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#include <<a href="qfont-h.html">qfont.h</a>>
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#include <<a href="qvbox-h.html">qvbox.h</a>>
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class MyWidget : public <a href="qvbox.html">QVBox</a>
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{
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public:
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MyWidget( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
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};
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<a name="f553"></a>MyWidget::MyWidget( <a href="qwidget.html">QWidget</a> *parent, const char *name )
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: <a href="qvbox.html">QVBox</a>( parent, name )
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{
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<a href="qpushbutton.html">QPushButton</a> *quit = new <a href="qpushbutton.html">QPushButton</a>( "Quit", this, "quit" );
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quit-><a href="qwidget.html#setFont">setFont</a>( QFont( "Times", 18, QFont::Bold ) );
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<a href="qobject.html#connect">connect</a>( quit, SIGNAL(<a href="qbutton.html#clicked">clicked</a>()), qApp, SLOT(<a href="qapplication.html#quit">quit</a>()) );
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<a href="qlcdnumber.html">QLCDNumber</a> *lcd = new <a href="qlcdnumber.html">QLCDNumber</a>( 2, this, "lcd" );
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<a href="qslider.html">QSlider</a> * slider = new <a href="qslider.html">QSlider</a>( Horizontal, this, "slider" );
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slider-><a href="qrangecontrol.html#setRange">setRange</a>( 0, 99 );
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slider-><a href="qslider.html#setValue">setValue</a>( 0 );
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<a href="qobject.html#connect">connect</a>( slider, SIGNAL(<a href="qslider.html#valueChanged">valueChanged</a>(int)), lcd, SLOT(<a href="qlcdnumber.html#display">display</a>(int)) );
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}
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int main( int argc, char **argv )
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{
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<a href="qapplication.html">QApplication</a> a( argc, argv );
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MyWidget w;
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a.<a href="qapplication.html#setMainWidget">setMainWidget</a>( &w );
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w.<a href="qwidget.html#show">show</a>();
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return a.<a href="qapplication.html#exec">exec</a>();
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}
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</pre>
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<p> <h2> Line-by-line Walkthrough
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</h2>
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<a name="1"></a><p> <pre> #include <<a href="qapplication-h.html">qapplication.h</a>>
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#include <<a href="qpushbutton-h.html">qpushbutton.h</a>>
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#include <<a href="qslider-h.html">qslider.h</a>>
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#include <<a href="qlcdnumber-h.html">qlcdnumber.h</a>>
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#include <<a href="qfont-h.html">qfont.h</a>>
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#include <<a href="qvbox-h.html">qvbox.h</a>>
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</pre>
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<p> Three new include files are shown here. qslider.h and qlcdnumber.h are there
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because we use two new widgets, <a href="qslider.html">QSlider</a> and <a href="qlcdnumber.html">QLCDNumber</a>. qvbox.h is
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here because we use Qt's automatic layout support.
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<p> <pre> class MyWidget : public <a href="qvbox.html">QVBox</a>
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{
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public:
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MyWidget( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
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};
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</pre>
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<p> <a name="constructor"></a>
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<pre> MyWidget::MyWidget( <a href="qwidget.html">QWidget</a> *parent, const char *name )
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: <a href="qvbox.html">QVBox</a>( parent, name )
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{
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</pre>
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<p> MyWidget is now derived from <a href="qvbox.html">QVBox</a> instead of <a href="qwidget.html">QWidget</a>. That way we use
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the layout of the QVBox (which places all of its children vertically
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inside itself). Resizes are now handled automatically by the QVBox and
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therefore by MyWidget, too.
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<p> <pre> <a href="qlcdnumber.html">QLCDNumber</a> *lcd = new <a href="qlcdnumber.html">QLCDNumber</a>( 2, this, "lcd" );
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</pre>
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<p> <tt>lcd</tt> is a QLCDNumber, a widget that displays numbers in an LCD-like
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fashion. This instance is set up to display two digits and to be a child of
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<em>this</em>. It is named "lcd".
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<p> <pre> <a href="qslider.html">QSlider</a> * slider = new <a href="qslider.html">QSlider</a>( Horizontal, this, "slider" );
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<a name="x2315"></a> slider-><a href="qrangecontrol.html#setRange">setRange</a>( 0, 99 );
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<a name="x2316"></a> slider-><a href="qslider.html#setValue">setValue</a>( 0 );
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</pre>
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<p> <a href="qslider.html">QSlider</a> is a classical slider; the user can use the widget to drag
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something to adjust an integer value in a range. Here we create a
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horizontal one, set its range to 0-99 (inclusive, see the <a href="qrangecontrol.html#setRange">QSlider::setRange</a>() documentation) and its initial value to 0.
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<p> <pre> <a name="x2317"></a><a name="x2314"></a> <a href="qobject.html#connect">connect</a>( slider, SIGNAL(<a href="qslider.html#valueChanged">valueChanged</a>(int)), lcd, SLOT(<a href="qlcdnumber.html#display">display</a>(int)) );
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</pre>
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<p> Here we use the <a href="signalsandslots.html">signal/slot mechanism</a>
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to connect the slider's valueChanged() signal to the LCD number's
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display() slot.
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<p> Whenever the slider's value changes it broadcasts the new value by
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emitting the valueChanged() signal. Because that signal is connected to
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the LCD number's display() slot, the slot is called when the signal is
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broadcast. Neither of the objects knows about the other. This is
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essential in component programming.
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<p> Slots are otherwise normal C++ member functions and follow the normal
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C++ access rules.
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<p> <h2> Behavior
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</h2>
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<a name="2"></a><p> The LCD number reflects everything you do to the slider, and the
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widget handles resizing well. Notice that the LCD number widget
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changes in size when the window is resized (because it can), but the
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others stay about the same (because otherwise they would look stupid).
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<p> (See <a href="tutorial1-01.html#compiling">Compiling</a> for how to create a
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makefile and build the application.)
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<p> <h2> Exercises
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</h2>
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<a name="3"></a><p> Try changing the LCD number to add more digits or <a href="qlcdnumber.html#setMode">to change mode.</a> You can even add four push
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buttons to set the number base.
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<p> You can also change the slider's range.
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<p> Perhaps it would have been better to use <a href="qspinbox.html">QSpinBox</a> than a slider?
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<p> Try to make the application quit when the LCD number overflows.
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<p> You're now ready for <a href="tutorial1-06.html">Chapter 6.</a>
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<p> [<a href="tutorial1-04.html">Previous tutorial</a>]
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[<a href="tutorial1-06.html">Next tutorial</a>]
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[<a href="tutorial.html">Main tutorial page</a>]
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<p>
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<!-- eof -->
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<p><address><hr><div align=center>
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<table width=100% cellspacing=0 border=0><tr>
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<td>Copyright © 2007
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<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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<td align=right><div align=right>Qt 3.3.8</div>
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</table></div></address></body>
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</html>
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