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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><html><head><meta name="robots" content="noindex"><title>
Qt Tutorial - Chapter 6
</title></head><body bgcolor="#ffffff">
<p>
<a href=index.html><img width=122 height=65 src=qtlogo.jpg alt="Qt logo" align=left border=0></a>
<center><img src=dochead.gif width=472 height=27></center>
<br clear=all>
<p>
<h1 align=center>Chapter 6: Building Blocks Galore!</h1><br clear="all">
<p>
<center><img src="t6.gif" 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="qscrollbar-h.html">qscrollbar.h</a>>
#include <<a href="qlcdnumber-h.html">qlcdnumber.h</a>>
#include <<a href="qfont-h.html">qfont.h</a>>
class LCDRange : public QWidget
{
public:
LCDRange( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
protected:
void resizeEvent( <a href="qresizeevent.html">QResizeEvent</a> * );
private:
<a href="qscrollbar.html">QScrollBar</a> *sBar;
<a href="qlcdnumber.html">QLCDNumber</a> *lcd;
};
LCDRange::LCDRange( <a href="qwidget.html">QWidget</a> *parent, const char *name )
: <a href="qwidget.html">QWidget</a>( parent, name )
{
lcd = new <a href="qlcdnumber.html">QLCDNumber</a>( 2, this, "lcd" );
lcd-><a href="qwidget.html#l2">move</a>( 0, 0 );
sBar = new <a href="qscrollbar.html">QScrollBar</a>( 0, 99, // range
1, 10, // line/page steps
0, // inital value
QScrollBar::Horizontal, // orientation
this, "scrollbar" );
<a href="qobject.html#f2">connect</a>( sBar, SIGNAL(valueChanged(int)), lcd, SLOT(display(int)) );
}
void <a name="399"></a>LCDRange::resizeEvent( <a href="qresizeevent.html">QResizeEvent</a> * )
{
sBar-><a href="qwidget.html#l5">setGeometry</a>( 0, <a href="qwidget.html#c0">height</a>() - 16, <a href="qwidget.html#b9">width</a>(), 16 );
lcd-><a href="qwidget.html#l4">resize</a>( <a href="qwidget.html#b9">width</a>(), sBar-><a href="qwidget.html#b6">y</a>() - 5 );
}
class MyWidget : public QWidget
{
public:
MyWidget( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
protected:
void resizeEvent( <a href="qresizeevent.html">QResizeEvent</a> * );
private:
<a href="qpushbutton.html">QPushButton</a> *quit;
LCDRange *value[16];
};
MyWidget::MyWidget( <a href="qwidget.html">QWidget</a> *parent, const char *name )
: <a href="qwidget.html">QWidget</a>( parent, name )
{
<a href="qwidget.html#c6">setMinimumSize</a>( 200, 300 );
quit = new <a href="qpushbutton.html">QPushButton</a>( "Quit", this, "quit" );
quit-><a href="qpushbutton.html#b4">setGeometry</a>( 10, 10, 75, 30 );
quit-><a href="qwidget.html#f9">setFont</a>( <a href="qfont.html">QFont</a>( "Times", 18, QFont::Bold ) );
<a href="qobject.html#f2">connect</a>( quit, SIGNAL(clicked()), qApp, SLOT(quit()) );
for( int i = 0 ; i < 16 ; i++ )
value[i] = new LCDRange( this );
}
void <a name="400"></a>MyWidget::resizeEvent( <a href="qresizeevent.html">QResizeEvent</a> * )
{
int startx = 10;
int starty = quit-><a href="qwidget.html#b6">y</a>() + quit-><a href="qwidget.html#c0">height</a>() + 10;
int valueWidth = (<a href="qwidget.html#b9">width</a>() - startx - 10 - 3*5)/4;
int valueHeight = (<a href="qwidget.html#c0">height</a>() - starty - 10 - 3*5)/4;
for( int i = 0 ; i < 16 ; i++ )
value[i]->setGeometry( startx + (i%4)*(5+valueWidth),
starty + (i/4)*(5+valueHeight),
valueWidth, valueHeight );
}
int main( int argc, char **argv )
{
<a href="qapplication.html">QApplication</a> a( argc, argv );
MyWidget w;
w.<a href="qwidget.html#l5">setGeometry</a>( 100, 100, 400, 400 );
a.<a href="qapplication.html#b9">setMainWidget</a>( &w );
w.<a href="qwidget.html#k2">show</a>();
return a.<a href="qapplication.html#c9">exec</a>();
}
</pre>
<p>
<h2>Line by Line Walk-Through</h2>
<p>
<pre>
class LCDRange : public QWidget
{
public:
LCDRange( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
protected:
void resizeEvent( <a href="qresizeevent.html">QResizeEvent</a> * );
private:
<a href="qscrollbar.html">QScrollBar</a> *sBar;
<a href="qlcdnumber.html">QLCDNumber</a> *lcd;
};
</pre>
<p>
The LCDRange widget is an encapsulation of a QScrollBar and a
QLCDNumber, connected together.
<p>
<pre>
LCDRange::LCDRange( <a href="qwidget.html">QWidget</a> *parent, const char *name )
: <a href="qwidget.html">QWidget</a>( parent, name )
{
lcd = new <a href="qlcdnumber.html">QLCDNumber</a>( 2, this, "lcd" );
lcd-><a href="qwidget.html#l2">move</a>( 0, 0 );
sBar = new <a href="qscrollbar.html">QScrollBar</a>( 0, 99, // range
1, 10, // line/page steps
0, // inital value
QScrollBar::Horizontal, // orientation
this, "scrollbar" );
<a href="qobject.html#f2">connect</a>( sBar, SIGNAL(valueChanged(int)), lcd, SLOT(display(int)) );
}
</pre>
<p>
This is essentially lifted straight from the <a
href="t5.html#constructor">MyWidget constructor</a> in chapter five. The
only difference is that <code>lcd</code> is now placed at coordinate 0,0 (the top
left corner of the LCDRange widget) since we're making a new widget and
don't want a border. If the widget's user wants a border, he/she can make
a border around the LCDRange.
<p>
<pre>
void <a name="399"></a>LCDRange::resizeEvent( <a href="qresizeevent.html">QResizeEvent</a> * )
{
sBar-><a href="qwidget.html#l5">setGeometry</a>( 0, <a href="qwidget.html#c0">height</a>() - 16, <a href="qwidget.html#b9">width</a>(), 16 );
lcd-><a href="qwidget.html#l4">resize</a>( <a href="qwidget.html#b9">width</a>(), sBar-><a href="qwidget.html#b6">y</a>() - 5 );
}
</pre>
<p>
Since LCDRange doesn't have either a border or quit button, the resize
event is simpler than <a href="t5.html#resize">the one in MyWidget.</a>
<p>
<pre>
private:
<a href="qpushbutton.html">QPushButton</a> *quit;
LCDRange *value[16];
};
</pre>
<p>
MyWidget now contains the familiar quit button and an array of 16
LCDRange pointers.
<p>
<pre>
for( int i = 0 ; i < 16 ; i++ )
value[i] = new LCDRange( this );
</pre>
<p>
In MyWidget's constructor, we create 16 LCDRanges, all with <code>this</code> as
parent. Remember that these will be deleted by Qt when MyWidget is
destroyed.
<p>
<pre>
void <a name="400"></a>MyWidget::resizeEvent( <a href="qresizeevent.html">QResizeEvent</a> * )
{
int startx = 10;
int starty = quit-><a href="qwidget.html#b6">y</a>() + quit-><a href="qwidget.html#c0">height</a>() + 10;
int valueWidth = (<a href="qwidget.html#b9">width</a>() - startx - 10 - 3*5)/4;
int valueHeight = (<a href="qwidget.html#c0">height</a>() - starty - 10 - 3*5)/4;
for( int i = 0 ; i < 16 ; i++ )
value[i]->setGeometry( startx + (i%4)*(5+valueWidth),
starty + (i/4)*(5+valueHeight),
valueWidth, valueHeight );
}
</pre>
<p>
In the resize event, we calculate and set the geometry of all 16
LCDRanges in a simple for loop.
<p>
First we calculate the top left position of the top left LCDRange.
We give it a 10 pixel border to the left and a 10 pixel border up
to the quit button (see <a href="coordsys.html">The Coordinate System</a>)
<p>
We then calculate the size of each LCDRange. We want a grid of 4x4
widgets with a 10 pixel border to the right and 5 pixels between
each one (i.e. 3 borders of 5 pixels in each direction).
Note that since we divide by the integer 4, we will get small roundoff
errors.
<p>
Next, we set each individual geometry in a simple loop. We calculate
the position using integer modulo and divide and remember to add 5
for the border between each one.
<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 scroll bar and LCD number in the
previous chapter. Again, the difference lies in the implementation.
<p>
<h2>Excercises</h2>
<p>
Change MyWidget so each LCDRange is guaranteed to be square.
<p>
Initialize each scroll bar with a different/random value on startup.
<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>]
<p><address><hr><div align="center">
<table width="100%" cellspacing="0" border="0"><tr>
<td>Copyright 1999 Troll Tech<td><a href="trademarks.html">Trademarks</a>
<td align="right"><div align="right">Qt version 1.45</div>
</table></div></address></body></html>
|
