数字时钟范例

数字时钟范例的屏幕截图

此范例还演示如何 QTimer 可以用于按定期间隔更新 Widget。

DigitalClock 类定义

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 类实现

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);
}

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.

最后，调用 QLCDNumber::display () 以更新 Widget。

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