- Qt 5.5
- Qt Widgets
- Digital Clock Example
- Qt 5.5.1 Reference Documentation

# Digital Clock Example

This example also demonstrates how QTimer can be used to update a widget at regular intervals.

## DigitalClock Class Definition

The `DigitalClock` class provides a clock widget showing the time with hours and minutes separated by a blinking colon. We subclass QLCDNumber and implement a private slot called `showTime()` to update the clock display:

    class DigitalClock : public QLCDNumber
    {
        Q_OBJECT

    public:
        DigitalClock(QWidget *parent = 0);

    private slots:
        void showTime();
    };

## DigitalClock Class Implementation

    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);
    }

In the constructor, we first change the look of the LCD numbers. The QLCDNumber::Filled 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 timeout() signal to the private `showTime()` slot so that the display is updated every second. Then, we call the `showTime()` slot; without this call, there would be a one-second delay at startup before the time is shown.

    void DigitalClock::showTime()
    {
        QTime time = QTime::currentTime();
        QString text = time.toString("hh:mm");
        if ((time.second() % 2) == 0)
            text[2] = ' ';
        display(text);
    }

The `showTime()` slot is called whenever the clock display needs to be updated.

The current time is converted into a string with the format "hh:mm". When QTime::second() is a even number, the colon in the string is replaced with a space. This makes the colon appear and vanish every other second.

Finally, we call QLCDNumber::display() to update the widget.

Files:

- widgets/digitalclock/digitalclock.cpp
- widgets/digitalclock/digitalclock.h
- widgets/digitalclock/main.cpp
- widgets/digitalclock/digitalclock.pro