![]() See also QBasicTimer, QTimerEvent, QObject::timerEvent(), Timers, Analog Clock Example, and Wiggly Example. Some operating systems limit the number of timers that may be used Qt tries to work around these limitations. See Timers for an overview of all three approaches. It is typically less cumbersome than using QObject::startTimer() directly. The disadvantage is that timerEvent() does not support such high-level features as single-shot timers or signals.Īnother alternative to using QTimer is to use QBasicTimer. Alternatives to QTimerĪn 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). If Qt is unable to deliver the requested number of timer clicks, it will silently discard some. 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 of timers depends on the underlying operating system and hardware. ![]() In many situations, they may time out late by a period of time that depends on the accuracy of the system timers. Timers will never time out earlier than the specified timeout value and they are not guaranteed to time out at the exact value specified. 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. 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. ProcessOneThing() will from then on be called repeatedly. This can be used to do heavy work while providing a snappy user interface: QTimer *timer = new QTimer( this) Ĭonnect(timer, SIGNAL(timeout()), this, SLOT(processOneThing())) Because of this, you must start and stop the timer in its thread it is not possible to start a timer from another thread.Īs 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. Qt uses the timer's thread affinity to determine which thread will emit the timeout() signal. To start an event loop from a non-GUI thread, use QThread::exec(). In multithreaded applications, you can use QTimer in any thread that has an event loop. You can also use the static QTimer::singleShot() function to call a slot after a specified interval: QTimer ::singleShot( 200, this, SLOT(updateCaption())) You can set a timer to time out only once by calling setSingleShot(true). From then on it will emit the timeout() signal at constant intervals.Įxample for a one second (1000 millisecond) timer (from the Analog Clock example): QTimer *timer = new QTimer( this) Ĭonnect(timer, SIGNAL(timeout()), this, SLOT(update())) įrom then on, the update() slot is called every second. To use it, create a QTimer, connect its timeout() signal to the appropriate slots, and call start(). The QTimer class provides a high-level programming interface for timers. ![]() The QTimer class provides repetitive and single-shot timers. ![]() 8 protected functions inherited from QObject.Reimplemented Protected Functions virtual void 7 static public members inherited from QObject. ![]() SingleShot ( int msec, QObject * receiver, const char * member ) 29 public functions inherited from QObject.List of all members, including inherited members. ![]()
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