QTimer

The QTimer class provides repetitive and single-shot timers. More…

Inheritance diagram of PySide2.QtCore.QTimer

Synopsis

Functions

Slots

Static functions

Detailed Description

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, &QTimer::timeout, this, QOverload<>::of(&AnalogClock::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, self.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’s thread affinity 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 possible, though the ordering between zero timers and other sources of events is unspecified. Zero timers can be used to do some work while still providing a snappy user interface:

timer = QTimer(self)
timer.timeout.connect(self.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 QThread s.

Accuracy and Timer Resolution

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 PreciseTimer , QTimer will try to keep the accuracy at 1 millisecond. Precise timers will also never time out earlier than expected.

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

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.

See also

QBasicTimer QTimerEvent timerEvent() Timers Analog Clock Example Wiggly Example

class PySide2.QtCore.QTimer([parent=None])
param parent:

PySide2.QtCore.QObject

Constructs a timer with the given parent .

PySide2.QtCore.QTimer.interval()
Return type:

int

This property holds the timeout interval in milliseconds.

The default value for this property is 0. A QTimer with a timeout interval of 0 will time out as soon as all the events in the window system’s event queue have been processed.

Setting the interval of an active timer changes its timerId() .

See also

singleShot

PySide2.QtCore.QTimer.isActive()
Return type:

bool

This boolean property is true if the timer is running; otherwise false.

PySide2.QtCore.QTimer.isSingleShot()
Return type:

bool

This property holds whether the timer is a single-shot timer.

A single-shot timer fires only once, non-single-shot timers fire every interval milliseconds.

The default value for this property is false .

See also

interval singleShot()

PySide2.QtCore.QTimer.remainingTime()
Return type:

int

This property holds the remaining time in milliseconds.

Returns the timer’s remaining value in milliseconds left until the timeout. If the timer is inactive, the returned value will be -1. If the timer is overdue, the returned value will be 0.

See also

interval

PySide2.QtCore.QTimer.setInterval(msec)
Parameters:

msec – int

This property holds the timeout interval in milliseconds.

The default value for this property is 0. A QTimer with a timeout interval of 0 will time out as soon as all the events in the window system’s event queue have been processed.

Setting the interval of an active timer changes its timerId() .

See also

singleShot

PySide2.QtCore.QTimer.setSingleShot(singleShot)
Parameters:

singleShot – bool

This property holds whether the timer is a single-shot timer.

A single-shot timer fires only once, non-single-shot timers fire every interval milliseconds.

The default value for this property is false .

See also

interval singleShot()

PySide2.QtCore.QTimer.setTimerType(atype)
Parameters:

atype – TimerType

This property holds controls the accuracy of the timer.

The default value for this property is Qt::CoarseTimer .

See also

TimerType

static PySide2.QtCore.QTimer.singleShot(arg__1, arg__2)
Parameters:

  • arg__1 – int

  • arg__2 – PyCallable

static PySide2.QtCore.QTimer.singleShot(msec, timerType, receiver, member)
Parameters:

This is an overloaded function.

This static function calls a slot after a given time interval.

It is very convenient to use this function because you do not need to bother with a timerEvent or create a local QTimer object.

The receiver is the receiving object and the member is the slot. The time interval is msec milliseconds. The timerType affects the accuracy of the timer.

See also

start()

static PySide2.QtCore.QTimer.singleShot(msec, receiver, member)
Parameters:

This static function calls a slot after a given time interval.

It is very convenient to use this function because you do not need to bother with a timerEvent or create a local QTimer object.

Example:

from PySide2.QtCore import QApplication, QTimer

def main():

    app = QApplication([])
    QTimer.singleShot(600000, app, SLOT('quit()'))
    ...
    return app.exec_()

This sample program automatically terminates after 10 minutes (600,000 milliseconds).

The receiver is the receiving object and the member is the slot. The time interval is msec milliseconds.

See also

setSingleShot() start()

PySide2.QtCore.QTimer.start()

This function overloads .

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

If the timer is already running, it will be stopped and restarted.

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

PySide2.QtCore.QTimer.start(msec)
Parameters:

msec – int

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

If the timer is already running, it will be stopped and restarted.

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

Note

Keeping the event loop busy with a zero-timer is bound to cause trouble and highly erratic behavior of the UI.

PySide2.QtCore.QTimer.stop()

Stops the timer.

See also

start()

PySide2.QtCore.QTimer.timerId()
Return type:

int

Returns the ID of the timer if the timer is running; otherwise returns -1.

PySide2.QtCore.QTimer.timerType()
Return type:

TimerType

This property holds controls the accuracy of the timer.

The default value for this property is Qt::CoarseTimer .

See also

TimerType