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6<title>Qt Tutorial - Chapter 6: Building Blocks Galore!</title>
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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 6: Building Blocks Galore!</h1>
33
34
35<p> <center><img src="t6.png" alt="Screenshot of tutorial six"></center>
36<p> This example shows how to encapsulate two widgets into a new component and
37how easy it is to use many widgets. For the first time, we use a custom
38widget as a child widget.
39<p> <a name="main"></a>
40<pre>/****************************************************************
41**
42** Qt tutorial 6
43**
44****************************************************************/
45
46#include &lt;<a href="qapplication-h.html">qapplication.h</a>&gt;
47#include &lt;<a href="qpushbutton-h.html">qpushbutton.h</a>&gt;
48#include &lt;<a href="qslider-h.html">qslider.h</a>&gt;
49#include &lt;<a href="qlcdnumber-h.html">qlcdnumber.h</a>&gt;
50#include &lt;<a href="qfont-h.html">qfont.h</a>&gt;
51#include &lt;<a href="qvbox-h.html">qvbox.h</a>&gt;
52#include &lt;<a href="qgrid-h.html">qgrid.h</a>&gt;
53
54class LCDRange : public <a href="qvbox.html">QVBox</a>
55{
56public:
57 LCDRange( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
58};
59
60<a name="f554"></a>LCDRange::LCDRange( <a href="qwidget.html">QWidget</a> *parent, const char *name )
61 : <a href="qvbox.html">QVBox</a>( parent, name )
62{
63 <a href="qlcdnumber.html">QLCDNumber</a> *lcd = new <a href="qlcdnumber.html">QLCDNumber</a>( 2, this, "lcd" );
64 <a href="qslider.html">QSlider</a> * slider = new <a href="qslider.html">QSlider</a>( Horizontal, this, "slider" );
65 slider-&gt;<a href="qrangecontrol.html#setRange">setRange</a>( 0, 99 );
66 slider-&gt;<a href="qslider.html#setValue">setValue</a>( 0 );
67 <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)) );
68}
69
70class MyWidget : public <a href="qvbox.html">QVBox</a>
71{
72public:
73 MyWidget( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
74};
75
76
77<a name="f555"></a>MyWidget::MyWidget( <a href="qwidget.html">QWidget</a> *parent, const char *name )
78 : <a href="qvbox.html">QVBox</a>( parent, name )
79{
80 <a href="qpushbutton.html">QPushButton</a> *quit = new <a href="qpushbutton.html">QPushButton</a>( "Quit", this, "quit" );
81 quit-&gt;<a href="qwidget.html#setFont">setFont</a>( QFont( "Times", 18, QFont::Bold ) );
82
83 <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>()) );
84
85 <a href="qgrid.html">QGrid</a> *grid = new <a href="qgrid.html">QGrid</a>( 4, this );
86
87 for( int r = 0 ; r &lt; 4 ; r++ )
88 for( int c = 0 ; c &lt; 4 ; c++ )
89 (void)new LCDRange( grid );
90}
91
92int main( int argc, char **argv )
93{
94 <a href="qapplication.html">QApplication</a> a( argc, argv );
95
96 MyWidget w;
97 a.<a href="qapplication.html#setMainWidget">setMainWidget</a>( &amp;w );
98 w.<a href="qwidget.html#show">show</a>();
99 return a.<a href="qapplication.html#exec">exec</a>();
100}
101</pre>
102
103
104
105<p> <h2> Line-by-line Walkthrough
106</h2>
107<a name="1"></a><p> <pre> class LCDRange : public <a href="qvbox.html">QVBox</a>
108 {
109 public:
110 LCDRange( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
111 };
112</pre>
113<p> The LCDRange widget is a widget without any API. It just has a
114constructor. This sort of widget is not very useful, so we'll add some API later.
115<p> <pre> LCDRange::LCDRange( <a href="qwidget.html">QWidget</a> *parent, const char *name )
116 : <a href="qvbox.html">QVBox</a>( parent, name )
117 {
118 <a href="qlcdnumber.html">QLCDNumber</a> *lcd = new <a href="qlcdnumber.html">QLCDNumber</a>( 2, this, "lcd" );
119 <a href="qslider.html">QSlider</a> * slider = new <a href="qslider.html">QSlider</a>( Horizontal, this, "slider" );
120 <a name="x2325"></a> slider-&gt;<a href="qrangecontrol.html#setRange">setRange</a>( 0, 99 );
121 <a name="x2326"></a> slider-&gt;<a href="qslider.html#setValue">setValue</a>( 0 );
122 <a name="x2327"></a><a name="x2324"></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)) );
123 }
124</pre>
125<p> This is lifted straight from the
126<a href="tutorial1-05.html#constructor">MyWidget constructor</a> in Chapter 5.
127The only differences are that the button is left out and the class
128is renamed.
129<p> <pre> class MyWidget : public <a href="qvbox.html">QVBox</a>
130 {
131 public:
132 MyWidget( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
133 };
134</pre>
135<p> MyWidget, too, contains no API except a constructor.
136<p> <pre> MyWidget::MyWidget( <a href="qwidget.html">QWidget</a> *parent, const char *name )
137 : <a href="qvbox.html">QVBox</a>( parent, name )
138 {
139 <a href="qpushbutton.html">QPushButton</a> *quit = new <a href="qpushbutton.html">QPushButton</a>( "Quit", this, "quit" );
140 <a name="x2328"></a> quit-&gt;<a href="qwidget.html#setFont">setFont</a>( QFont( "Times", 18, QFont::Bold ) );
141
142 <a name="x2321"></a> <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>()) );
143</pre>
144<p> The push button that used to be in what is now LCDRange has been
145separated so that we can have one "Quit" button and many LCDRange
146objects.
147<p> <pre> <a href="qgrid.html">QGrid</a> *grid = new <a href="qgrid.html">QGrid</a>( 4, this );
148</pre>
149<p> We create a <a href="qgrid.html">QGrid</a> object with four columns. The QGRid widget
150automatically arranges its children in rows and columns; you can
151specify the number of rows or of columns, and QGrid will discover its
152new children and fit them into the grid.
153<p> <pre> for( int r = 0 ; r &lt; 4 ; r++ )
154 for( int c = 0 ; c &lt; 4 ; c++ )
155 (void)new LCDRange( grid );
156</pre>
157<p> Four columns, four rows.
158<p> We create 4*4 LCDRanges, all of which are children of the grid object.
159The QGrid widget will arrange them.
160<p> <pre> }
161</pre>
162<p> That's all.
163<p> <h2> Behavior
164</h2>
165<a name="2"></a><p> This program shows how easy it is to use many widgets at a time. Each
166one behaves like the slider and LCD number in the previous
167chapter. Again, the difference lies in the implementation.
168<p> (See <a href="tutorial1-01.html#compiling">Compiling</a> for how to create a
169makefile and build the application.)
170<p> <h2> Exercises
171</h2>
172<a name="3"></a><p> Initialize each slider with a different/random value on startup.
173<p> The source contains three occurrences of "4". What happens if you
174change the one in the <a href="qgrid.html">QGrid</a> constructor call? What about the other
175two? Why is this?
176<p> You're now ready for <a href="tutorial1-07.html">Chapter 7.</a>
177<p> [<a href="tutorial1-05.html">Previous tutorial</a>]
178[<a href="tutorial1-07.html">Next tutorial</a>]
179[<a href="tutorial.html">Main tutorial page</a>]
180<p>
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184<td>Copyright &copy; 2007
185<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
186<td align=right><div align=right>Qt 3.3.8</div>
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