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<title>Qt 4.6: Digital Clock Example</title>
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<td align="left" valign="top" width="32"><a href="http://qt.nokia.com/"><img src="images/qt-logo.png" align="left" border="0" /></a></td>
<td width="1"> </td><td class="postheader" 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="functions.html"><font color="#004faf">All Functions</font></a> · <a href="overviews.html"><font color="#004faf">Overviews</font></a></td></tr></table><h1 class="title">Digital Clock Example<br /><span class="subtitle"></span>
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<p>Files:</p>
<ul>
<li><a href="widgets-digitalclock-digitalclock-cpp.html">widgets/digitalclock/digitalclock.cpp</a></li>
<li><a href="widgets-digitalclock-digitalclock-h.html">widgets/digitalclock/digitalclock.h</a></li>
<li><a href="widgets-digitalclock-main-cpp.html">widgets/digitalclock/main.cpp</a></li>
<li><a href="widgets-digitalclock-digitalclock-pro.html">widgets/digitalclock/digitalclock.pro</a></li>
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<p>The Digital Clock example shows how to use <a href="qlcdnumber.html">QLCDNumber</a> to display a number with LCD-like digits.</p>
<p align="center"><img src="images/digitalclock-example.png" alt="Screenshot of the Digital Clock example" /></p><p>This example also demonstrates how <a href="qtimer.html">QTimer</a> can be used to update a widget at regular intervals.</p>
<a name="digitalclock-class-definition"></a>
<h2>DigitalClock Class Definition</h2>
<p>The <tt>DigitalClock</tt> class provides a clock widget showing the time with hours and minutes separated by a blinking colon. We subclass <a href="qlcdnumber.html">QLCDNumber</a> and implement a private slot called <tt>showTime()</tt> to update the clock display:</p>
<pre> class DigitalClock : public QLCDNumber
{
Q_OBJECT
public:
DigitalClock(QWidget *parent = 0);
private slots:
void showTime();
};</pre>
<a name="digitalclock-class-implementation"></a>
<h2>DigitalClock Class Implementation</h2>
<pre> DigitalClock::DigitalClock(QWidget *parent)
: QLCDNumber(parent)
{
setSegmentStyle(Filled);
QTimer *timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), this, SLOT(showTime()));
timer->start(1000);
showTime();
setWindowTitle(tr("Digital Clock"));
resize(150, 60);
}</pre>
<p>In the constructor, we first change the look of the LCD numbers. The <a href="qlcdnumber.html#SegmentStyle-enum">QLCDNumber::Filled</a> style produces raised segments filled with the foreground color (typically black). We also set up a one-second timer to keep track of the current time, and we connect its <a href="qtimer.html#timeout">timeout()</a> signal to the private <tt>showTime()</tt> slot so that the display is updated every second. Then, we call the <tt>showTime()</tt> slot; without this call, there would be a one-second delay at startup before the time is shown.</p>
<pre> void DigitalClock::showTime()
{
QTime time = QTime::currentTime();
QString text = time.toString("hh:mm");
if ((time.second() % 2) == 0)
text[2] = ' ';
display(text);
}</pre>
<p>The <tt>showTime()</tt> slot is called whenever the clock display needs to be updated.</p>
<p>The current time is converted into a string with the format "hh:mm". When <a href="qtime.html#second">QTime::second</a>() is a even number, the colon in the string is replaced with a space. This makes the colon appear and vanish every other second.</p>
<p>Finally, we call <a href="qlcdnumber.html#intValue-prop">QLCDNumber::display</a>() to update the widget.</p>
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