It's equivalent to calling QObject::connect(timer, &QTimer::timeout, context, slot, connectionType). template QMetaObject::Connection QTimer:: callOnTimeout(const QObject * context, Functor slot, Qt::ConnectionType connectionType = Qt::AutoConnection)Ĭreates a connection from the timeout() signal to slot to be placed in a specific event loop of context, and returns a handle to the connection. See also QObject::connect() and timeout(). It's equivalent to calling QObject::connect(timer, &QTimer::timeout, timer, slot, connectionType). template QMetaObject::Connection QTimer:: callOnTimeout( Functor slot, Qt::ConnectionType connectionType = Qt::AutoConnection)Ĭreates a connection of type connectionType from the timeout() signal to slot, and returns a handle to the connection. It can be used in signal connections but cannot be emitted by the user. This signal is emitted when the timer times out. Note: Keeping the event loop busy with a zero-timer is bound to cause trouble and highly erratic behavior of the UI. 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 is 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). In such a case of timeout overrun, Qt will emit timeout() only once, even if multiple timeouts have expired, and then will resume the original interval. Precise timers will also never time out earlier than expected.įor Qt::CoarseTimer and Qt::Ver圜oarseTimer 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::Ver圜oarseTimer.Īll timer types may time out later than expected if the system is busy or unable to provide the requested accuracy. For Qt::PreciseTimer, QTimer will try to keep the accuracy at 1 millisecond. The accuracy also depends on the timer type.

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. This is the traditional way of implementing heavy work in GUI applications, but as multithreading is nowadays becoming available on more and more platforms, we expect that zero-millisecond QTimer objects 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 the user interface and stop the timer as soon as it has done all its work. Connect(timer, & QTimer ::timeout, this, &Foo ::processOneThing) įrom then on, processOneThing() will be called repeatedly.

Itimer virtual exmaple