You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
298 lines
14 KiB
298 lines
14 KiB
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
|
|
<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/tutorial.doc:868 -->
|
|
<html>
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
|
|
<title>TQt Tutorial - Chapter 8: Preparing for Battle</title>
|
|
<style type="text/css"><!--
|
|
fn { margin-left: 1cm; text-indent: -1cm; }
|
|
a:link { color: #004faf; text-decoration: none }
|
|
a:visited { color: #672967; text-decoration: none }
|
|
body { background: #ffffff; color: black; }
|
|
--></style>
|
|
</head>
|
|
<body>
|
|
|
|
<table border="0" cellpadding="0" cellspacing="0" width="100%">
|
|
<tr bgcolor="#E5E5E5">
|
|
<td valign=center>
|
|
<a href="index.html">
|
|
<font color="#004faf">Home</font></a>
|
|
| <a href="classes.html">
|
|
<font color="#004faf">All Classes</font></a>
|
|
| <a href="mainclasses.html">
|
|
<font color="#004faf">Main Classes</font></a>
|
|
| <a href="annotated.html">
|
|
<font color="#004faf">Annotated</font></a>
|
|
| <a href="groups.html">
|
|
<font color="#004faf">Grouped Classes</font></a>
|
|
| <a href="functions.html">
|
|
<font color="#004faf">Functions</font></a>
|
|
</td>
|
|
<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>TQt Tutorial - Chapter 8: Preparing for Battle</h1>
|
|
|
|
|
|
<p> <center><img src="t8.png" alt="Screenshot of tutorial eight"></center>
|
|
<p> In this example, we introduce the first custom widget that can paint
|
|
itself. We also add a useful keyboard interface (with two lines of
|
|
code).
|
|
<p> <ul>
|
|
<li> <a href="t8-lcdrange-h.html">t8/lcdrange.h</a> contains the LCDRange class definition.
|
|
<li> <a href="t8-lcdrange-cpp.html">t8/lcdrange.cpp</a> contains the LCDRange implementation.
|
|
<li> <a href="t8-cannon-h.html">t8/cannon.h</a> contains the CannonField class definition.
|
|
<li> <a href="t8-cannon-cpp.html">t8/cannon.cpp</a> contains the CannonField implementation.
|
|
<li> <a href="t8-main-cpp.html">t8/main.cpp</a> contains MyWidget and main.
|
|
</ul>
|
|
<p> <h2> Line-by-line Walkthrough
|
|
</h2>
|
|
<a name="1"></a><p> <h3> <a href="t8-lcdrange-h.html">t8/lcdrange.h</a>
|
|
</h3>
|
|
<a name="1-1"></a><p> This file is very similar to the lcdrange.h in Chapter 7. We have added
|
|
one slot: setRange().
|
|
<p>
|
|
|
|
<p> <pre> void setRange( int minVal, int maxVal );
|
|
</pre>
|
|
<p> We now add the possibility of setting the range of the LCDRange.
|
|
Until now, it has been fixed at 0..99.
|
|
<p> <h3> <a href="t8-lcdrange-cpp.html">t8/lcdrange.cpp</a>
|
|
</h3>
|
|
<a name="1-2"></a><p>
|
|
|
|
<p> There is a change to the constructor (we'll discuss that later).
|
|
<p> <pre> void LCDRange::setRange( int minVal, int maxVal )
|
|
{
|
|
if ( minVal < 0 || maxVal > 99 || minVal > maxVal ) {
|
|
<a href="ntqapplication.html#qWarning">qWarning</a>( "LCDRange::setRange(%d,%d)\n"
|
|
"\tRange must be 0..99\n"
|
|
"\tand minVal must not be greater than maxVal",
|
|
minVal, maxVal );
|
|
return;
|
|
}
|
|
<a name="x2334"></a> slider-><a href="ntqrangecontrol.html#setRange">setRange</a>( minVal, maxVal );
|
|
}
|
|
</pre>
|
|
<p> SetRange() sets the range of the slider in the LCDRange. Because we
|
|
have set up the <a href="ntqlcdnumber.html">TQLCDNumber</a> to always display two digits, we want to
|
|
limit the possible range of <tt>minVal</tt> and <tt>maxVal</tt> to 0..99 to avoid
|
|
overflow of the TQLCDNumber. (We could have allowed values down to -9
|
|
but chose not to.) If the arguments are illegal, we use TQt's
|
|
<a href="ntqapplication.html#qWarning">qWarning</a>() function to issue a warning to the user and return
|
|
immediately. tqWarning() is a printf-like function that by default
|
|
sends its output to <tt>stderr</tt>. If you want, you can install your own handler
|
|
function using <a href="ntqapplication.html#qInstallMsgHandler">::qInstallMsgHandler</a>().
|
|
<p> <h3> <a href="t8-cannon-h.html">t8/cannon.h</a>
|
|
</h3>
|
|
<a name="1-3"></a><p> CannonField is a new custom widget that knows how to display itself.
|
|
<p>
|
|
|
|
<p> <pre> class CannonField : public <a href="ntqwidget.html">TQWidget</a>
|
|
{
|
|
<a href="metaobjects.html#TQ_OBJECT">TQ_OBJECT</a>
|
|
public:
|
|
CannonField( <a href="ntqwidget.html">TQWidget</a> *parent=0, const char *name=0 );
|
|
</pre>
|
|
<p> CannonField inherits <a href="ntqwidget.html">TQWidget</a>, and we use the same idiom as for LCDRange.
|
|
<p> <pre> int angle() const { return ang; }
|
|
<a href="ntqsizepolicy.html">TQSizePolicy</a> sizePolicy() const;
|
|
|
|
public slots:
|
|
void setAngle( int degrees );
|
|
|
|
signals:
|
|
void angleChanged( int );
|
|
</pre>
|
|
<p> For the time being, CannonField only contains an angle value for which we
|
|
provide an interface using the same idiom as for value in LCDRange.
|
|
<p> <pre> protected:
|
|
void paintEvent( <a href="qpaintevent.html">TQPaintEvent</a> * );
|
|
</pre>
|
|
<p> This is the second of the many event handlers in TQWidget that we
|
|
encounter. This virtual function is called by TQt whenever a widget needs
|
|
to update itself (i.e., paint the widget's surface).
|
|
<p> <h3> <a href="t8-cannon-cpp.html">t8/cannon.cpp</a>
|
|
</h3>
|
|
<a name="1-4"></a><p>
|
|
|
|
<p> <pre> CannonField::CannonField( <a href="ntqwidget.html">TQWidget</a> *parent, const char *name )
|
|
: <a href="ntqwidget.html">TQWidget</a>( parent, name )
|
|
{
|
|
</pre>
|
|
<p> Again, we use the same idiom as for LCDRange in the previous chapter.
|
|
<p> <pre> ang = 45;
|
|
<a href="ntqwidget.html#setPalette">setPalette</a>( TQPalette( TQColor( 250, 250, 200) ) );
|
|
}
|
|
</pre>
|
|
<p> The constructor initializes the angle value to 45 degrees and sets a
|
|
custom palette for this widget.
|
|
<p> This palette uses the indicated color as background and picks other
|
|
colors suitably. (For this widget only the background and text
|
|
colors will actually be used.)
|
|
<p> <pre> void CannonField::setAngle( int degrees )
|
|
{
|
|
if ( degrees < 5 )
|
|
degrees = 5;
|
|
if ( degrees > 70 )
|
|
degrees = 70;
|
|
if ( ang == degrees )
|
|
return;
|
|
ang = degrees;
|
|
<a href="ntqwidget.html#repaint">repaint</a>();
|
|
emit angleChanged( ang );
|
|
}
|
|
</pre>
|
|
<p> This function sets the angle value. We have chosen a legal range of
|
|
5..70 and adjust the given number of degrees accordingly. We have
|
|
chosen not to issue a warning if the new angle is out of range.
|
|
<p> If the new angle equals the old one, we return immediately. It is
|
|
important to only emit the signal angleChanged() when the angle <em>really</em> has changed.
|
|
<p> Then we set the new angle value and repaint our widget. The <a href="ntqwidget.html#repaint">TQWidget::repaint</a>() function clears the widget (usually filling it with
|
|
its background color) and sends a paint event to the widget. This
|
|
results in a call to the paint event function of the widget.
|
|
<p> Finally, we emit the angleChanged() signal to tell the outside world
|
|
that the angle has changed. The <tt>emit</tt> keyword is unique to TQt and
|
|
not regular C++ syntax. In fact, it is a macro.
|
|
<p> <pre> <a name="x2336"></a>void CannonField::<a href="ntqwidget.html#paintEvent">paintEvent</a>( <a href="qpaintevent.html">TQPaintEvent</a> * )
|
|
{
|
|
<a href="ntqstring.html">TQString</a> s = "Angle = " + TQString::number( ang );
|
|
<a href="ntqpainter.html">TQPainter</a> p( this );
|
|
<a name="x2335"></a> p.<a href="ntqpainter.html#drawText">drawText</a>( 200, 200, s );
|
|
}
|
|
</pre>
|
|
<p> This is our first attempt to write a paint event handler. The event
|
|
argument contains a description of the paint event. <a href="qpaintevent.html">TQPaintEvent</a>
|
|
contains the region in the widget that must be updated. For the time
|
|
being, we will be lazy and just paint everything.
|
|
<p> Our code displays the angle value in the widget at a fixed position.
|
|
First we create a <a href="ntqstring.html">TQString</a> with some text and the angle; then we create
|
|
a <a href="ntqpainter.html">TQPainter</a> operating on this widget and use it to paint the string.
|
|
We'll come back to TQPainter later; it can do a great many things.
|
|
<p> <h3> <a href="t8-main-cpp.html">t8/main.cpp</a>
|
|
</h3>
|
|
<a name="1-5"></a><p>
|
|
|
|
<p> <pre> #include "cannon.h"
|
|
</pre>
|
|
<p> We include our new class.
|
|
<p> <pre> class MyWidget: public <a href="ntqwidget.html">TQWidget</a>
|
|
{
|
|
public:
|
|
MyWidget( <a href="ntqwidget.html">TQWidget</a> *parent=0, const char *name=0 );
|
|
};
|
|
</pre>
|
|
<p> This time we include a single LCDRange and a CannonField in our top-level
|
|
widget.
|
|
<p> <pre> LCDRange *angle = new LCDRange( this, "angle" );
|
|
</pre>
|
|
<p> In the constructor, we create and set up our LCDRange.
|
|
<p> <pre> angle->setRange( 5, 70 );
|
|
</pre>
|
|
<p> We set the LCDRange to accept ranges from 5 to 70 degrees.
|
|
<p> <pre> CannonField *cannonField
|
|
= new CannonField( this, "cannonField" );
|
|
</pre>
|
|
<p> We create our CannonField.
|
|
<p> <pre> <a href="ntqobject.html#connect">connect</a>( angle, SIGNAL(valueChanged(int)),
|
|
cannonField, SLOT(setAngle(int)) );
|
|
<a href="ntqobject.html#connect">connect</a>( cannonField, SIGNAL(angleChanged(int)),
|
|
angle, SLOT(setValue(int)) );
|
|
</pre>
|
|
<p> Here we connect the valueChanged() signal of the LCDRange to the
|
|
setAngle() slot of the CannonField. This will update CannonField's angle
|
|
value whenever the user operates the LCDRange. We also make the reverse
|
|
connection so that changing the angle in the CannonField will update the
|
|
LCDRange value. In our example we never change the angle of the
|
|
CannonField directly; but by doing the last connect() we ensure that no
|
|
future changes will disrupt the synchronization between those two values.
|
|
<p> This illustrates the power of component programming and proper
|
|
encapsulation.
|
|
<p> Notice how important it is to emit the angleChanged() signal only when
|
|
the angle actually changes. If both the LCDRange and the CannonField
|
|
had omitted this check, the program would have entered an infinite
|
|
loop upon the first change of one of the values.
|
|
<p> <pre> <a href="qgridlayout.html">TQGridLayout</a> *grid = new <a href="qgridlayout.html">TQGridLayout</a>( this, 2, 2, 10 );
|
|
//2x2, 10 pixel border
|
|
</pre>
|
|
<p> So far we have used the no-assembly-required <a href="ntqvbox.html">TQVBox</a> and <a href="ntqgrid.html">TQGrid</a> widgets
|
|
for geometry management. Now, however, we want to have a little more
|
|
control over the layout, and we switch to the more powerful <a href="qgridlayout.html">TQGridLayout</a>
|
|
class. TQGridLayout isn't a widget; it is a different class that can
|
|
manage the children of <em>any</em> widget.
|
|
<p> As the comment indicates, we create a two-by-two array with ten pixel
|
|
borders. (The constructor for <a href="qgridlayout.html">TQGridLayout</a> can be a little cryptic,
|
|
so it's good to put in such comments.)
|
|
<p> <pre> <a name="x2337"></a> grid-><a href="qgridlayout.html#addWidget">addWidget</a>( quit, 0, 0 );
|
|
</pre>
|
|
<p> We add the Quit button in the top-left cell of the grid: 0, 0.
|
|
<p> <pre> grid-><a href="qgridlayout.html#addWidget">addWidget</a>( angle, 1, 0, TQt::AlignTop );
|
|
</pre>
|
|
<p> We put the angle LCDRange in the bottom-left cell, aligned to the top
|
|
of its cell. (This alignment is one of the things TQGridLayout allows
|
|
but TQGrid does not allow.)
|
|
<p> <pre> grid-><a href="qgridlayout.html#addWidget">addWidget</a>( cannonField, 1, 1 );
|
|
</pre>
|
|
<p> We put the CannonField object in the bottom-right cell. (The top-
|
|
right cell is empty.)
|
|
<p> <pre> <a name="x2338"></a> grid-><a href="qgridlayout.html#setColStretch">setColStretch</a>( 1, 10 );
|
|
</pre>
|
|
<p> We tell <a href="qgridlayout.html">TQGridLayout</a> that the right column (column 1) is stretchable.
|
|
Because the left column isn't (it has <a href="layout.html#stretch-factor">stretch factor</a> 0, the default
|
|
value), TQGridLayout will try to let the left-hand widgets' sizes be
|
|
unchanged and will resize just the CannonField when the MyWidget is
|
|
resized.
|
|
<p> <pre> angle->setValue( 60 );
|
|
</pre>
|
|
<p> We set an initial angle value. Note that this will trigger the
|
|
connection from LCDRange to CannonField.
|
|
<p> <pre> <a name="x2339"></a> angle-><a href="ntqwidget.html#setFocus">setFocus</a>();
|
|
</pre>
|
|
<p> Our last action is to set <tt>angle</tt> to have <a href="focus.html#keyboard-focus">keyboard focus</a> so that
|
|
keyboard input will go to the LCDRange widget by default.
|
|
<p> LCDRange does not contain any keyPressEvent(), so that would seem not
|
|
to be terribly useful. However, its constructor just got a new line:
|
|
<p>
|
|
|
|
<pre> <a href="ntqwidget.html#setFocusProxy">setFocusProxy</a>( slider );
|
|
</pre>
|
|
<p> The LCDRange sets the slider to be its focus proxy. That means that
|
|
when someone (the program or the user) wants to give the LCDRange
|
|
keyboard focus, the slider should take care of it. <a href="ntqslider.html">TQSlider</a> has a decent
|
|
keyboard interface, so with just one line of code we've given LCDRange
|
|
one.
|
|
<p> <h2> Behavior
|
|
</h2>
|
|
<a name="2"></a><p> The keyboard now does something - the arrow keys, Home, End, PageUp
|
|
and PageDown all do something vaguely sensible.
|
|
<p> When the slider is operated, the CannonField displays the new angle
|
|
value. Upon resizing, CannonField is given as much space as possible.
|
|
<p> On Windows machines with an 8-bit display the new background color is
|
|
dithered to death. The next chapter works around this.
|
|
<p> (See <a href="tutorial1-07.html#compiling">Compiling</a> for how to create a
|
|
makefile and build the application.)
|
|
<p> <h2> Exercises
|
|
</h2>
|
|
<a name="3"></a><p> Try to resize the window. What happens if you make it really narrow
|
|
or really squat?
|
|
<p> If you remove the AlignTop, what happens to the LCDRange's position
|
|
and size? Why?
|
|
<p> If you give the left-hand column a non-zero stretch factor, what
|
|
happens when you resize the window?
|
|
<p> Leave out the setFocus() call. Which behavior do you prefer?
|
|
<p> Try to change "Quit" to "&Quit" in the <a href="ntqbutton.html#setText">TQButton::setText</a>() call. How
|
|
does the button's look change? What happens if you press Alt+Q while
|
|
the program's running? (It is Meta+Q on a few keyboards.)
|
|
<p> Center the text in the CannonField.
|
|
<p> You're now ready for <a href="tutorial1-09.html">Chapter 9.</a>
|
|
<p> [<a href="tutorial1-07.html">Previous tutorial</a>]
|
|
[<a href="tutorial1-09.html">Next tutorial</a>]
|
|
[<a href="tutorial.html">Main tutorial page</a>]
|
|
<p>
|
|
<!-- eof -->
|
|
<p><address><hr><div align=center>
|
|
<table width=100% cellspacing=0 border=0><tr>
|
|
<td>Copyright © 2007
|
|
<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
|
|
<td align=right><div align=right>TQt 3.3.8</div>
|
|
</table></div></address></body>
|
|
</html>
|