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<title>Qt Tutorial - Chapter 6: Building Blocks Galore!</title>
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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 6: Building Blocks Galore!</h1>
<p> <center><img src="t6.png" alt="Screenshot of tutorial six"></center>
<p> This example shows how to encapsulate two widgets into a new component and
how easy it is to use many widgets. For the first time, we use a custom
widget as a child widget.
<p> <a name="main"></a>
<pre>/****************************************************************
**
** Qt tutorial 6
**
****************************************************************/
#include <<a href="qapplication-h.html">qapplication.h</a>>
#include <<a href="qpushbutton-h.html">qpushbutton.h</a>>
#include <<a href="qslider-h.html">qslider.h</a>>
#include <<a href="qlcdnumber-h.html">qlcdnumber.h</a>>
#include <<a href="qfont-h.html">qfont.h</a>>
#include <<a href="qvbox-h.html">qvbox.h</a>>
#include <<a href="qgrid-h.html">qgrid.h</a>>
class LCDRange : public <a href="qvbox.html">QVBox</a>
{
public:
LCDRange( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
};
<a name="f554"></a>LCDRange::LCDRange( <a href="qwidget.html">QWidget</a> *parent, const char *name )
: <a href="qvbox.html">QVBox</a>( parent, name )
{
<a href="qlcdnumber.html">QLCDNumber</a> *lcd = new <a href="qlcdnumber.html">QLCDNumber</a>( 2, this, "lcd" );
<a href="qslider.html">QSlider</a> * slider = new <a href="qslider.html">QSlider</a>( Horizontal, this, "slider" );
slider-><a href="qrangecontrol.html#setRange">setRange</a>( 0, 99 );
slider-><a href="qslider.html#setValue">setValue</a>( 0 );
<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)) );
}
class MyWidget : public <a href="qvbox.html">QVBox</a>
{
public:
MyWidget( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
};
<a name="f555"></a>MyWidget::MyWidget( <a href="qwidget.html">QWidget</a> *parent, const char *name )
: <a href="qvbox.html">QVBox</a>( parent, name )
{
<a href="qpushbutton.html">QPushButton</a> *quit = new <a href="qpushbutton.html">QPushButton</a>( "Quit", this, "quit" );
quit-><a href="qwidget.html#setFont">setFont</a>( QFont( "Times", 18, QFont::Bold ) );
<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>()) );
<a href="qgrid.html">QGrid</a> *grid = new <a href="qgrid.html">QGrid</a>( 4, this );
for( int r = 0 ; r < 4 ; r++ )
for( int c = 0 ; c < 4 ; c++ )
(void)new LCDRange( grid );
}
int main( int argc, char **argv )
{
<a href="qapplication.html">QApplication</a> a( argc, argv );
MyWidget w;
a.<a href="qapplication.html#setMainWidget">setMainWidget</a>( &w );
w.<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> class LCDRange : public <a href="qvbox.html">QVBox</a>
{
public:
LCDRange( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
};
</pre>
<p> The LCDRange widget is a widget without any API. It just has a
constructor. This sort of widget is not very useful, so we'll add some API later.
<p> <pre> LCDRange::LCDRange( <a href="qwidget.html">QWidget</a> *parent, const char *name )
: <a href="qvbox.html">QVBox</a>( parent, name )
{
<a href="qlcdnumber.html">QLCDNumber</a> *lcd = new <a href="qlcdnumber.html">QLCDNumber</a>( 2, this, "lcd" );
<a href="qslider.html">QSlider</a> * slider = new <a href="qslider.html">QSlider</a>( Horizontal, this, "slider" );
<a name="x2325"></a> slider-><a href="qrangecontrol.html#setRange">setRange</a>( 0, 99 );
<a name="x2326"></a> slider-><a href="qslider.html#setValue">setValue</a>( 0 );
<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)) );
}
</pre>
<p> This is lifted straight from the
<a href="tutorial1-05.html#constructor">MyWidget constructor</a> in Chapter 5.
The only differences are that the button is left out and the class
is renamed.
<p> <pre> class MyWidget : public <a href="qvbox.html">QVBox</a>
{
public:
MyWidget( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
};
</pre>
<p> MyWidget, too, contains no API except a constructor.
<p> <pre> MyWidget::MyWidget( <a href="qwidget.html">QWidget</a> *parent, const char *name )
: <a href="qvbox.html">QVBox</a>( parent, name )
{
<a href="qpushbutton.html">QPushButton</a> *quit = new <a href="qpushbutton.html">QPushButton</a>( "Quit", this, "quit" );
<a name="x2328"></a> quit-><a href="qwidget.html#setFont">setFont</a>( QFont( "Times", 18, QFont::Bold ) );
<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>()) );
</pre>
<p> The push button that used to be in what is now LCDRange has been
separated so that we can have one "Quit" button and many LCDRange
objects.
<p> <pre> <a href="qgrid.html">QGrid</a> *grid = new <a href="qgrid.html">QGrid</a>( 4, this );
</pre>
<p> We create a <a href="qgrid.html">QGrid</a> object with four columns. The QGRid widget
automatically arranges its children in rows and columns; you can
specify the number of rows or of columns, and QGrid will discover its
new children and fit them into the grid.
<p> <pre> for( int r = 0 ; r < 4 ; r++ )
for( int c = 0 ; c < 4 ; c++ )
(void)new LCDRange( grid );
</pre>
<p> Four columns, four rows.
<p> We create 4*4 LCDRanges, all of which are children of the grid object.
The QGrid widget will arrange them.
<p> <pre> }
</pre>
<p> That's all.
<p> <h2> Behavior
</h2>
<a name="2"></a><p> This program shows how easy it is to use many widgets at a time. Each
one behaves like the slider and LCD number in the previous
chapter. Again, the difference lies in the implementation.
<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> Initialize each slider with a different/random value on startup.
<p> The source contains three occurrences of "4". What happens if you
change the one in the <a href="qgrid.html">QGrid</a> constructor call? What about the other
two? Why is this?
<p> You're now ready for <a href="tutorial1-07.html">Chapter 7.</a>
<p> [<a href="tutorial1-05.html">Previous tutorial</a>]
[<a href="tutorial1-07.html">Next tutorial</a>]
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