Provides repetitive and single-shot timers. More...

Inheritance diagram for QTimer:

Public Signals
void	timeout ()

Public Signals inherited from QObject
void	destroyed (QObject *obj=nullptr)

void	objectNameChanged (const QString &objectName)

Public Slots
void	start ()

void	start (int msec)

void	stop ()

Public Slots inherited from QObject
void	deleteLater ()

Public Methods
	QTimer (QObject *parent=nullptr)

	~QTimer ()

int	interval () const

bool	isActive () const

bool	isSingleShot () const

int	remainingTime () const

void	setInterval (int msec)

void	setSingleShot (bool value)

void	setTimerType (Qt::TimerType timerType)

int	timerId () const

Qt::TimerType	timerType () const

Public Methods inherited from QObject
	QObject (QObject *parent=nullptr)

	~QObject ()

bool	blockSignals (bool block)

const QList< QObject * > &	children () const

bool	connect (const QObject *sender, const QString &signalMethod, const QString &location, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

bool	connect (const QObject *sender, const QString &signalMethod, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

bool	disconnect (const QObject *receiver, const QString &slotMethod=QString ()) const

bool	disconnect (const QString &signalMethod, const QString &location, const QObject *receiver=nullptr, const QString &slotMethod=QString ()) const

bool	disconnect (const QString &signalMethod=QString (), const QObject *receiver=nullptr, const QString &slotMethod=QString ()) const

void	dumpObjectInfo ()

void	dumpObjectTree ()

QList< QString >	dynamicPropertyNames () const

virtual bool	event (QEvent *event)

virtual bool	eventFilter (QObject watched, QEvent event)

template<typename T >
T	findChild (const QString &childName=QString ()) const

template<class T >
QList< T >	findChildren (const QRegularExpression &regExp, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

template<class T >
QList< T >	findChildren (const QString &childName=QString (), Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

bool	inherits (const QString &className) const

void	installEventFilter (QObject *filterObj)

bool	isWidgetType () const

bool	isWindowType () const

void	killTimer (int id)

const QMetaObject *	metaObject () const

void	moveToThread (QThread *targetThread)

QString	objectName () const

QObject *	parent () const

template<class T = QVariant>
T	property (const QString &name) const

void	removeEventFilter (QObject *obj)

void	setObjectName (const QString &name)

void	setParent (QObject *parent)

bool	setProperty (const QString &name, const QVariant &value)

bool	signalsBlocked () const

int	startTimer (int interval, Qt::TimerType timerType=Qt::CoarseTimer)

QThread *	thread () const

Static Public Methods
static void	singleShot (int msec, const QObject *receiver, const QString &slotMethod)

template<typename T >
static void	singleShot (int msec, QObject *receiver, T slotMethod)

static void	singleShot (int msec, Qt::TimerType timerType, const QObject *receiver, const QString &slotMethod)

template<typename T >
static void	singleShot (int msec, Qt::TimerType timerType, QObject *receiver, T slotMethod)

template<typename Receiver , typename SlotClass , typename SlotReturn >
static void	singleShot (int msec, Qt::TimerType timerType, Receiver receiver, SlotReturn (SlotClass::slotMethod)())

template<typename T >
static void	singleShot (int msec, Qt::TimerType timerType, T slotMethod)

template<typename Receiver , typename SlotClass , typename SlotReturn >
static void	singleShot (int msec, Receiver receiver, SlotReturn (SlotClass::slotMethod)())

template<typename T >
static void	singleShot (int msec, T slotMethod)

Static Public Methods inherited from QObject
static bool	connect (const QObject sender, const QMetaMethod &signalMethod, const QObject receiver, const QMetaMethod &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

static bool	connect (const QObject sender, const QString &signalMethod, const QObject receiver, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection, const QString &location=QString ())

static bool	connect (const QObject sender, const QString &signalMethod, const QString &location, const QObject receiver, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class SlotClass , class... SlotArgs, class SlotReturn >
static bool	connect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver receiver, SlotReturn (SlotClass::slotMethod)(SlotArgs...), Qt::ConnectionType type=Qt::AutoConnection)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class T >
static bool	connect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver *receiver, T slotLambda, Qt::ConnectionType type=Qt::AutoConnection)

static bool	disconnect (const QObject sender, const QMetaMethod &signalMethod, const QObject receiver, const QMetaMethod &slotMethod)

static bool	disconnect (const QObject sender, const QString &signalMethod, const QObject receiver, const QString &slotMethod)

static bool	disconnect (const QObject sender, const QString &signalMethod, const QString &location, const QObject receiver, const QString &slotMethod)

static bool	disconnect (const QObject sender, std::nullptr_t, const QObject receiver, std::nullptr_t)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class SlotClass , class... SlotArgs, class SlotReturn >
static bool	disconnect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver receiver, SlotReturn (SlotClass::slotMethod)(SlotArgs...))

template<class Sender , class SignalClass , class... SignalArgs, class Receiver >
static bool	disconnect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver *receiver, std::nullptr_t slotMethod=nullptr)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class T >
static bool	disconnect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver *receiver, T slotMethod)

static QMetaObject &	staticMetaObject ()

static QString	tr (const char text, const char comment=nullptr, std::optional< int > numArg=std::optional< int >())

Protected Methods
void	timerEvent (QTimerEvent *event) override

Protected Methods inherited from QObject
virtual void	childEvent (QChildEvent *event)

virtual void	connectNotify (const QMetaMethod &signalMethod) const

virtual void	customEvent (QEvent *event)

virtual void	disconnectNotify (const QMetaMethod &signalMethod) const

bool	isSignalConnected (const QMetaMethod &signalMethod) const

int	receivers (const QString &signal) const

QObject *	sender () const

int	senderSignalIndex () const

Properties
	active

	interval

	remainingTime

	singleShot

	timerType

Properties inherited from QObject
	objectName

Additional Inherited Members
Related Functions inherited from QObject
T	qobject_cast (QObject *object)

	QObjectList

Detailed Description

The QTimer class provides repetitive and single-shot timers. This class provide a high level programming interface for timers.

First create a QTimer and then connect the timeout() signal to the appropriate slots. Call start() on the timer. From then on the timer will emit the timeout() signal at constant intervals.

QTimer *timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), this, SLOT(update()));
timer->start(1000);

In the example above, the update() slot is called once 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, 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 QThread::exec(). CopperSpice 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 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 *timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), this, SLOT(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 CopperSpice 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.

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 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. When this occurs the activated() signal will only be emitted 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 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. Ref to Timers for an overview of all three approaches.

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

See also: QBasicTimer, QTimerEvent, QObject::timerEvent(), Timers

Constructor & Destructor Documentation

QTimer::QTimer ( QObject * parent = nullptr )

explicit

Constructs a timer with the given parent.

QTimer::~QTimer ( )

Destroys the timer.

Method Documentation

int QTimer::interval ( ) const

inline

Returns the value of the property interval.

bool QTimer::isActive ( ) const

inline

Returns true if the timer is running or pending, otherwise returns false. This is a getter method for the active property.

bool QTimer::isSingleShot ( ) const

inline

Returns the value of the property singleShot.

See also: singleShot(), singleShot, interval

int QTimer::remainingTime ( ) const

Returns the value of the property remainingTime.

void QTimer::setInterval ( int msec )

Sets the value of the property to msec.

void QTimer::setSingleShot ( bool value )

inline

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: isSingleShot(), singleShot(), interval

void QTimer::setTimerType ( Qt::TimerType timerType )

inline

Sets the value of the property to timerType.

void QTimer::singleShot	(	int	msec,
		const QObject *	receiver,
		const QString &	slotMethod
	)

static

If msec is greater than 2000 the timerType will be Qt::CoarseTimer, otherwise it will be Qt::PreciseTimer.

Refer to singleShot() for more documentation.

template<typename T >

void QTimer::singleShot	(	int	msec,
		QObject *	receiver,
		T	slotMethod
	)

static

If msec is greater than 2000 the timerType will be Qt::CoarseTimer, otherwise it will be Qt::PreciseTimer.

Refer to singleShot() for more documentation.

void QTimer::singleShot	(	int	msec,
		Qt::TimerType	timerType,
		const QObject *	receiver,
		const QString &	slotMethod
	)

static

A static method which calls a slot after a given time interval. This is a convenient way to invoke a slot without needing to add a timerEvent or create a local QTimer object. The time interval is msec milliseconds. The timeType is affects the accuracy of the timer. The receiver is the receiving object and the slotMethod is the slot.

If the receiver is destroyed before the interval msec occurs, this method will not be called. This method will be invoked in the thread of the receiver. The receiver's thread must have a running event loop.

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

#include <QApplication>
#include <QTimer>
 
int main(int argc, char *argv[]) {
   QApplication app(argc, argv);
   QTimer::singleShot(600000, &app, SLOT(quit()));
 
   // ...
 
   return app.exec();
}

See also: setSingleShot(), start()

template<typename T >

void QTimer::singleShot	(	int	msec,
		Qt::TimerType	timerType,
		QObject *	receiver,
		T	slotMethod
	)

static

Refer to singleShot() for more documentation.

template<typename Receiver , typename SlotClass , typename SlotReturn >

void QTimer::singleShot	(	int	msec,
		Qt::TimerType	timerType,
		Receiver *	receiver,
		SlotReturn (SlotClass::*)()	slotMethod
	)

static

Refer to singleShot() for more documentation.

template<typename T >

void QTimer::singleShot	(	int	msec,
		Qt::TimerType	timerType,
		T	slotMethod
	)

static

Refer to singleShot() for more documentation.

template<typename Receiver , typename SlotClass , typename SlotReturn >

void QTimer::singleShot	(	int	msec,
		Receiver *	receiver,
		SlotReturn (SlotClass::*)()	slotMethod
	)

static

If msec is greater than 2000 the timerType will be Qt::CoarseTimer, otherwise it will be Qt::PreciseTimer.

Refer to singleShot() for more documentation.

See also: isSingleShot(), singleShot, interval

template<typename T >

void QTimer::singleShot	(	int	msec,
		T	slotMethod
	)

static

If msec is greater than 2000 the timerType will be Qt::CoarseTimer, otherwise it will be Qt::PreciseTimer.

Refer to singleShot() for more documentation.

void QTimer::start ( )

slot

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.

void QTimer::start ( int msec )

slot

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.

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(), stop()

void QTimer::timerEvent ( QTimerEvent * event )

overrideprotectedvirtual

Reimplemented from QObject::timerEvent()

int QTimer::timerId ( ) const

inline

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

Qt::TimerType QTimer::timerType ( ) const

inline

Returns the value of the property timerType.

Property Documentation

QTimer::active

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

Properties	Class Methods
read	isActive

QTimer::interval

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

Properties	Class Methods
read	interval
write	setInterval

QTimer::remainingTime

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

Properties	Class Methods
read	remainingTime

QTimer::singleShot

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.

See also: interval

Properties	Class Methods
read	isSingleShot
write	setSingleShot

QTimer::timerType

This property contains an enum value which indicate the accuracy level of the timer. The default value for this property is Qt::CoarseTimer.

See also: Qt::TimerType

Properties	Class Methods
read	timerType
write	setTimerType

Public Signals

Public Slots

Public Methods

Static Public Methods

Protected Methods

Properties

Additional Inherited Members

Detailed Description

Accuracy and Timer Resolution

Alternatives to QTimer

Constructor & Destructor Documentation

Method Documentation

Property Documentation