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java.lang.Objectcom.trolltech.qt.internal.QSignalEmitterInternal
com.trolltech.qt.QSignalEmitter
com.trolltech.qt.QtJambiObject
com.trolltech.qt.core.QObject
com.trolltech.qt.core.QTimer
public class QTimer
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):
The following code example is written in c++.
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 QTimer::singleShot()
function to call a slot after a specified interval:
QTimer.singleShot(200, this, "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(). Qt uses the 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); timer.timeout.connect(this, "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 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.
QBasicTimer
, QTimerEvent
, QObject::timerEvent()
, Timers, Analog Clock Example, and Wiggly Example.
Nested Class Summary |
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Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter |
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QSignalEmitter.AbstractSignal, QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9 |
Nested classes/interfaces inherited from class com.trolltech.qt.internal.QSignalEmitterInternal |
---|
com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal |
Field Summary | |
---|---|
QSignalEmitter.Signal0 |
timeout
|
Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal |
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currentSender |
Constructor Summary | |
---|---|
QTimer()
Constructs a timer with the given parent. |
|
QTimer(QObject parent)
Constructs a timer with the given parent. |
Method Summary | |
---|---|
int |
interval()
This property holds the timeout interval in milliseconds. |
boolean |
isActive()
This boolean property is true if the timer is running; otherwise false. |
boolean |
isSingleShot()
This property holds whether the timer is a single-shot timer. |
void |
setInterval(int msec)
This property holds the timeout interval in milliseconds. |
void |
setSingleShot(boolean singleShot)
This property holds whether the timer is a single-shot timer. |
static void |
singleShot(int msec,
QObject obj,
java.lang.String method)
This static function calls a slot after a given time interval. |
void |
start()
Starts or restarts the timer with the timeout specified in interval . |
void |
start(int msec)
Starts or restarts the timer with a timeout interval of msec milliseconds. |
void |
stop()
Stops the timer. |
int |
timerId()
Returns the ID of the timer if the timer is running; otherwise returns -1. |
Methods inherited from class com.trolltech.qt.core.QObject |
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childEvent, children, connectSlotsByName, customEvent, disposeLater, dumpObjectInfo, dumpObjectTree, dynamicPropertyNames, event, eventFilter, findChild, findChild, findChild, findChildren, findChildren, findChildren, findChildren, indexOfProperty, installEventFilter, isWidgetType, killTimer, moveToThread, objectName, parent, properties, property, removeEventFilter, setObjectName, setParent, setProperty, startTimer, timerEvent, toString, userProperty |
Methods inherited from class com.trolltech.qt.QtJambiObject |
---|
dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr |
Methods inherited from class com.trolltech.qt.QSignalEmitter |
---|
blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread |
Methods inherited from class com.trolltech.qt.internal.QSignalEmitterInternal |
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__qt_signalInitialization |
Methods inherited from class java.lang.Object |
---|
clone, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Methods inherited from interface com.trolltech.qt.QtJambiInterface |
---|
disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership |
Field Detail |
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public final QSignalEmitter.Signal0 timeout
Constructor Detail |
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public QTimer()
public QTimer(QObject parent)
Method Detail |
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public final int interval()
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()
.
singleShot
.
public final boolean isActive()
public final boolean isSingleShot()
interval
milliseconds. interval
, and singleShot()
.
public final void setInterval(int msec)
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()
.
singleShot
.
public final void setSingleShot(boolean singleShot)
interval
milliseconds. interval
, and singleShot()
.
public final void start()
interval
. If singleShot
is true, the timer will be activated only once.
public final void start(int msec)
public final void stop()
start()
.
public final int timerId()
public static void singleShot(int msec, QObject obj, java.lang.String method)
It is very convenient to use this function because you do not need to bother with a QObject.timerEvent() or create a local QTimer object.
Example:
#include <QApplication>
#include <QTimer>
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QTimer::singleShot(600000, &app, SLOT(quit()));
...
return app.exec();
}
This sample program automatically terminates after 10 minutes (600,000 milliseconds).
The obj is the receiving object and the member is the slot. The time interval is msec milliseconds.
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