數字時鍾範例

數字時鍾範例展示如何使用 QLCDNumber 顯示具有類似 LCD 數字的數。

數字時鍾範例的屏幕截圖

此範例還演示如何 QTimer 可以用於按定期間隔更新 Widget。

DigitalClock 類定義

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 類實現

DigitalClock::DigitalClock(QWidget *parent)
    : QLCDNumber(parent)
{
    setSegmentStyle(Filled);
    QTimer *timer = new QTimer(this);
    connect(timer, &QTimer::timeout, this, &DigitalClock::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.

最後，調用 QLCDNumber::display () 以更新 Widget。

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