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QTimer

Synopsis

Functions

Slots

Signals

Static functions

Detailed Description

The PySide.QtCore.QTimer class provides repetitive and single-shot timers.

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

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

timer = QTimer(self)
self.connect(timer, SIGNAL("timeout()"), self.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 QTimer.singleShot() function to call a slot after a specified interval:

QTimer.singleShot(200, self.updateCaption)

In multithreaded applications, you can use PySide.QtCore.QTimer in any thread that has an event loop. To start an event loop from a non-GUI thread, use QThread.exec() . Qt uses the timer’s thread affinity to determine which thread will emit the PySide.QtCore.QTimer.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 PySide.QtCore.QTimer with a timeout of 0 will time out as soon as all the events in the window system’s event queue have been processed. This can be used to do heavy work while providing a snappy user interface:

timer = QTimer(self)
timer.timeout.connect(self.processOneThing)
timer.start()

processOneThing() will from then on 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 widgets 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; multithreading is now becoming available on more and more platforms, and we expect that zero-millisecond QTimers will gradually be replaced by PySide.QtCore.QThread s.

Accuracy and Timer Resolution

Timers will never time out earlier than the specified timeout value and they are not guaranteed to time out at the exact value specified. In many situations, they may time out late by a period of time that depends on the accuracy of the system timers.

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.

If Qt is unable to deliver the requested number of timer clicks, it will silently discard some.

Alternatives to QTimer

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

Another alternative to using PySide.QtCore.QTimer is to use PySide.QtCore.QBasicTimer . It is typically less cumbersome than using QObject.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

PySide.QtCore.QBasicTimer PySide.QtCore.QTimerEvent QObject.timerEvent() Timers Analog Clock Example Wiggly Example

class PySide.QtCore.QTimer([parent=None])
Parameters:parent – PySide.QtCore.QObject

Constructs a timer with the given parent .

PySide.QtCore.QTimer.interval()
Return type:PySide.QtCore.int

This property holds the timeout interval in milliseconds.

The default value for this property is 0. A PySide.QtCore.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 PySide.QtCore.QTimer.timerId() .

See also

PySide.QtCore.QTimer.singleShot()

PySide.QtCore.QTimer.isActive()
Return type:PySide.QtCore.bool

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

PySide.QtCore.QTimer.isSingleShot()
Return type:PySide.QtCore.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 PySide.QtCore.QTimer.interval() milliseconds.

See also

PySide.QtCore.QTimer.interval() PySide.QtCore.QTimer.singleShot()

PySide.QtCore.QTimer.setInterval(msec)
Parameters:msec – PySide.QtCore.int

This property holds the timeout interval in milliseconds.

The default value for this property is 0. A PySide.QtCore.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 PySide.QtCore.QTimer.timerId() .

See also

PySide.QtCore.QTimer.singleShot()

PySide.QtCore.QTimer.setSingleShot(singleShot)
Parameters:singleShot – PySide.QtCore.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 PySide.QtCore.QTimer.interval() milliseconds.

See also

PySide.QtCore.QTimer.interval() PySide.QtCore.QTimer.singleShot()

static PySide.QtCore.QTimer.singleShot(arg__1, arg__2)
Parameters:
  • arg__1 – PySide.QtCore.int
  • arg__2 – PyCallable
static PySide.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 PySide.QtCore.QObject.timerEvent() or create a local PySide.QtCore.QTimer object.

Example:

from PySide.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

PySide.QtCore.QTimer.setSingleShot() PySide.QtCore.QTimer.start()

PySide.QtCore.QTimer.start(msec)
Parameters:msec – PySide.QtCore.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 PySide.QtCore.QTimer.singleShot() is true, the timer will be activated only once.

PySide.QtCore.QTimer.start()

This function overloads PySide.QtCore.QTimer.start() .

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

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

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

PySide.QtCore.QTimer.stop()

Stops the timer.

See also

PySide.QtCore.QTimer.start()

PySide.QtCore.QTimer.timeout()
PySide.QtCore.QTimer.timerId()
Return type:PySide.QtCore.int

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

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