Qtimer Signal Slot Example



  1. Qtimer Timeout
  2. Qtimer Update Ui
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You can set a timer interval for a QTimer object and a signal, timeout, will be emitted at that interval. For example, if you set an interval of 2000 milliseconds, the QTimer object emits its timeout signal every two seconds while the timer is active. C (Cpp) QTimer::start - 30 examples found. These are the top rated real world C (Cpp) examples of QTimer::start extracted from open source projects. You can rate examples to help us improve the quality of examples. This signal does nothing, by itself; it must be connected to a slot, which is an object that acts as a recipient for a signal and, given one, acts on it. Connecting Built-In PySide/PyQt Signals. Qt widgets have a number of signals built in. For example, when a QPushButton is clicked, it emits its clicked signal.

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

Inherits QObject.

Properties

  • singleShot : bool

Public Functions

  • QTimer ( QObject * parent = 0 )
  • int interval () const
  • bool isSingleShot () const
  • void setSingleShot ( bool singleShot )
  • 28 public functions inherited from QObject

Public Slots

  • void start ()
  • 1 public slot inherited from QObject

Signals

  • 1 signal inherited from QObject

Static Public Members

  • void singleShot ( int msec, QObject * receiver, const char * member )

Additional Inherited Members

  • 7 protected functions inherited from QObject

Detailed Description

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):

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:

As a special case, a 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:

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 QThreads.

Note that QTimer's accuracy depends on the underlying operating system and hardware. Most platforms support an accuracy of 1 millisecond, but Windows 98 supports only 55. If Qt is unable to deliver the requested number of timer clicks, it will silently discard some.

An alternative to using QTimer is to call QObject::startTimer() for your object and reimplement the QObject::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 to using QTimer is to use 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 QBasicTimer, QTimerEvent, QObject::timerEvent(), and Timers.

Property Documentation

interval : 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().

Access functions:

  • void setInterval ( int msec )

See also singleShot.

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.

Access functions:

  • void setSingleShot ( bool singleShot )

See also interval and singleShot().

Member Function Documentation

QTimer::QTimer ( QObject * parent = 0 )

Constructs a timer with the given parent.

QTimer::~QTimer ()

Destroys the timer.

bool QTimer::isActive () const

Returns true if the timer is running (pending); otherwise returns false.

void QTimer::singleShot ( int msec, QObject * receiver, const char * member ) [static]

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:

This sample program automatically terminates after 10 minutes (600000 milliseconds).

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

Note: This function is reentrant.

See also setSingleShot() and start().

void QTimer::start ( int msec ) [slot]

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

void QTimer::start () [slot]

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

void QTimer::stop () [slot]

Stops the timer.

See also start().

void QTimer::timeout () [signal]

This signal is emitted when the timer times out.

See also interval, start(), and stop().

int QTimer::timerId () const

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


Synopsis¶

Functions¶

  • def interval ()
  • def isActive ()
  • def isSingleShot ()
  • def setInterval (msec)
  • def setSingleShot (singleShot)
  • def timerId ()

Signals¶

  • def timeout ()

Qtimer Timeout

Static functions¶

  • def singleShot (arg__1, arg__2)
  • def singleShot (msec, receiver, member)

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):

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:

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 threadaffinity 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:

Qtimer Update Ui

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.QBasicTimerPySide.QtCore.QTimerEventQObject.timerEvent()TimersAnalog Clock ExampleWiggly Example

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

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.setInterval(msec)
Parameters:msecPySide.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() .

PySide.QtCore.QTimer.setSingleShot(singleShot)
Parameters:singleShotPySide.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

static PySide.QtCore.QTimer.singleShot(msec, receiver, member)
Qtimer Signal Slot Example
Parameters:
  • msecPySide.QtCore.int
  • receiverPySide.QtCore.QObject
  • member – str

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:

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

static PySide.QtCore.QTimer.singleShot(arg__1, arg__2)
Parameters:
  • arg__1PySide.QtCore.int
  • arg__2PyCallable
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 PySide.QtCore.QTimer.singleShot() is true, the timer will be activated only once.

PySide.QtCore.QTimer.start(msec)
Parameters:msecPySide.QtCore.int

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

PySide.QtCore.QTimer.stop()

Stops the timer.

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.