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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>
Qt Tutorial - Chapter 6: Building Blocks Galore!
</title></head><body bgcolor="#ffffff">
<p>
<table width="100%">
<tr><td><a href="index.html">
<img width="100" height="100" src="qtlogo.png"
alt="Home" border="0"><img width="100"
height="100" src="face.png" alt="Home" border="0">
</a><td valign=top><div align=right><img src="dochead.png" width="472" height="27"><br>
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</div>
</table>
<p>
<h1 align=center>Chapter 6: Building Blocks Galore!</h1><br clear="all">
<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 QVBox
{
public:
LCDRange( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
};
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#f2409c">setRange</a>( 0, 99 );
slider-><a href="qslider.html#a03234">setValue</a>( 0 );
<a href="qobject.html#7f8e37">connect</a>( slider, SIGNAL(valueChanged(int)), lcd, SLOT(display(int)) );
}
class MyWidget : public QVBox
{
public:
MyWidget( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
};
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#c52788">setFont</a>( <a href="qfont.html">QFont</a>( "Times", 18, QFont::Bold ) );
<a href="qobject.html#7f8e37">connect</a>( quit, SIGNAL(clicked()), qApp, SLOT(quit()) );
<a href="qgrid.html">QGrid</a> *grid = new <a href="qgrid.html">QGrid</a>( 4, this );
for( int c = 0 ; c < 4 ; c++ )
for( int r = 0 ; r < 4 ; r++ )
(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#7ad759">setMainWidget</a>( &w );
w.<a href="qwidget.html#200ee5">show</a>();
return a.<a href="qapplication.html#84c7bf">exec</a>();
}
</pre>
<p>
<h2>Line by Line Walk-Through</h2> <pre>
class LCDRange : public QVBox
{
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 later on
we'll add some API. <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" );
slider-><a href="qrangecontrol.html#f2409c">setRange</a>( 0, 99 );
slider-><a href="qslider.html#a03234">setValue</a>( 0 );
<a href="qobject.html#7f8e37">connect</a>( slider, SIGNAL(valueChanged(int)), lcd, SLOT(display(int)) );
}
</pre>
<p>
This is lifted straight from the <a
href="t5.html#constructor">MyWidget constructor</a> in chapter five.
The only differences are that the button is left out and the class
renamed. <pre>
class MyWidget : public QVBox
{
public:
MyWidget( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
};
</pre>
<p>
MyWidget, too, contains no API except a constructor. <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" );
quit-><a href="qwidget.html#c52788">setFont</a>( <a href="qfont.html">QFont</a>( "Times", 18, QFont::Bold ) );
<a href="qobject.html#7f8e37">connect</a>( quit, SIGNAL(clicked()), qApp, SLOT(quit()) );
</pre>
<p>
The push button that used to be in what's now LCDRange has been
separated, so that we can have one "Quit" button and many LCDRange
objects. <pre>
<a href="qgrid.html">QGrid</a> *grid = new <a href="qgrid.html">QGrid</a>( 4, this );
</pre>
<p>
We create a QGrid 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. <pre>
for( int c = 0 ; c < 4 ; c++ )
for( int r = 0 ; r < 4 ; r++ )
(void)new LCDRange( grid );
</pre>
<p>
Four columns, for rows.
<p>
We create 4*4 LCDRanges, all of which children of the grid object.
The QGrid widget will arrange them. <pre>
}
</pre>
<p>
That's all.
<p>
<h2>Behavior</h2>
<p>
This program shows how easy it is to use many widgets at a time. Each
single one behaves like the slider and LCD number in the previous
chapter. Again, the difference lies in the implementation.
<p>
<h2>Exercises</h2>
<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 may now go on to <a href="t7.html">chapter seven.</a>
<p>
[<a href="t5.html">Previous tutorial</a>]
[<a href="t7.html">Next tutorial</a>]
[<a href="tutorial.html">Main tutorial page</a>]
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<td>Copyright 2001 Trolltech<td><a href="http://www.trolltech.com/trademarks.html">Trademarks</a>
<td align="right"><div align="right">Qt version 2.3.2</div>
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