QTimer露

PyQt5.QtCore.QTimer: Inherits from QObject.

Description露

The QTimer class provides repetitive and single-shot timers.

The QTimer class provides a high-level programming interface for timers. To use it, create a QTimer, connect its timeout signal to the appropriate slots, and call start(). From then on, it will emit the timeout signal at constant intervals.

Example for a one second (1000 millisecond) timer (from the Analog Clock example):

#     QTimer *timer = new QTimer(this);

#     connect(timer, SIGNAL(timeout()), this, SLOT(update()));

#     timer->start(1000);

From then on, the update() slot is called every second.

You can set a timer to time out only once by calling setSingleShot()(true). You can also use the static singleShot() function to call a slot after a specified interval:

#     QTimer::singleShot(200, this, SLOT(updateCaption()));

In multithreaded applications, you can use QTimer in any thread that has an event loop. To start an event loop from a non-GUI thread, use exec(). Qt uses the timer鈥檚 thread() to determine which thread will emit the timeout signal. Because of this, you must start and stop the timer in its thread; it is not possible to start a timer from another thread.

As a special case, a QTimer with a timeout of 0 will time out as soon as all the events in the window system鈥檚 event queue have been processed. This can be used to do heavy work while providing a snappy user interface:

#     QTimer *timer = new QTimer(this);

#     connect(timer, SIGNAL(timeout()), this, SLOT(processOneThing()));

#     timer->start();

From then on, processOneThing() will be called repeatedly. It should be written in such a way that it always returns quickly (typically after processing one data item) so that Qt can deliver events to the user interface and stop the timer as soon as it has done all its work. This is the traditional way of implementing heavy work in GUI applications, but as multithreading is nowadays becoming available on more and more platforms, we expect that zero-millisecond QTimer objects will gradually be replaced by QThreads.

Accuracy and Timer Resolution露

The accuracy of timers depends on the underlying operating system and hardware. Most platforms support a resolution of 1 millisecond, though the accuracy of the timer will not equal this resolution in many real-world situations.

The accuracy also depends on the timer type. For Qt::PreciseTimer, QTimer will try to keep the accuracy at 1 millisecond. Precise timers will also never time out earlier than expected.

For Qt::CoarseTimer and Qt::VeryCoarseTimer types, QTimer may wake up earlier than expected, within the margins for those types: 5% of the interval for Qt::CoarseTimer and 500 ms for Qt::VeryCoarseTimer.

All timer types may time out later than expected if the system is busy or unable to provide the requested accuracy. In such a case of timeout overrun, Qt will emit timeout only once, even if multiple timeouts have expired, and then will resume the original interval.

Alternatives to QTimer露

An alternative to using QTimer is to call startTimer() for your object and reimplement the timerEvent() event handler in your class (which must inherit QObject). The disadvantage is that timerEvent() does not support such high-level features as single-shot timers or signals.

Another alternative is QBasicTimer. It is typically less cumbersome than using startTimer() directly. See Timers for an overview of all three approaches.

Some operating systems limit the number of timers that may be used; Qt tries to work around these limitations.

Methods露

__init__(parent: QObject = None): Constructs a timer with the given parent.

interval() → int: See also

setInterval().

isActive() → bool: TODO

isSingleShot() → bool: TODO

remainingTime() → int: TODO

setInterval(int): See also

interval().

setSingleShot(bool): See also

singleShot().

setTimerType(TimerType): TODO

@staticmethod singleShot(int, PYQT_SLOT): TODO

@staticmethod singleShot(int, TimerType, PYQT_SLOT): TODO

start()

This function overloads .

Starts or restarts the timer with the timeout specified in interval().

If the timer is already running, it will be stop() and restarted.

If singleShot() is true, the timer will be activated only once.

start(int)

Starts or restarts the timer with a timeout interval of msec milliseconds.

If the timer is already running, it will be stop() and restarted.

If singleShot() is true, the timer will be activated only once.

stop(): Stops the timer.

See also

start().

timerEvent(QTimerEvent): TODO

timerId() → int: TODO

timerType() → TimerType: TODO

Signals露

timeout(): TODO