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Diffstat (limited to 'src/corelib/doc/src/timers.qdoc')
| -rw-r--r-- | src/corelib/doc/src/timers.qdoc | 140 |
1 files changed, 56 insertions, 84 deletions
diff --git a/src/corelib/doc/src/timers.qdoc b/src/corelib/doc/src/timers.qdoc index f54d2fa457..dc205a47b9 100644 --- a/src/corelib/doc/src/timers.qdoc +++ b/src/corelib/doc/src/timers.qdoc @@ -1,46 +1,22 @@ -/**************************************************************************** -** -** Copyright (C) 2016 The Qt Company Ltd. -** Contact: https://www.qt.io/licensing/ -** -** This file is part of the documentation of the Qt Toolkit. -** -** $QT_BEGIN_LICENSE:FDL$ -** Commercial License Usage -** Licensees holding valid commercial Qt licenses may use this file in -** accordance with the commercial license agreement provided with the -** Software or, alternatively, in accordance with the terms contained in -** a written agreement between you and The Qt Company. For licensing terms -** and conditions see https://www.qt.io/terms-conditions. For further -** information use the contact form at https://www.qt.io/contact-us. -** -** GNU Free Documentation License Usage -** Alternatively, this file may be used under the terms of the GNU Free -** Documentation License version 1.3 as published by the Free Software -** Foundation and appearing in the file included in the packaging of -** this file. Please review the following information to ensure -** the GNU Free Documentation License version 1.3 requirements -** will be met: https://www.gnu.org/licenses/fdl-1.3.html. -** $QT_END_LICENSE$ -** -****************************************************************************/ +// Copyright (C) 2016 The Qt Company Ltd. +// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only /*! \page timers.html \title Timers \brief How to use Qt timers in your application. - \ingroup best-practices + \ingroup how-to QObject, the base class of all Qt objects, provides the basic timer support in Qt. With QObject::startTimer(), you start a timer with an interval in milliseconds as argument. The function - returns a unique integer timer ID. The timer will now fire at + returns a unique integral timer ID. The timer will then fire at regular intervals until you explicitly call QObject::killTimer() - with the timer ID. + with that timer ID. For this mechanism to work, the application must run in an event - loop. You start an event loop with QApplication::exec(). When a + loop. You cat start an event loop with QApplication::exec(). When a timer fires, the application sends a QTimerEvent, and the flow of control leaves the event loop until the timer event is processed. This implies that a timer cannot fire while your application is @@ -55,69 +31,65 @@ stop all timers in the object's thread; it is not possible to start timers for objects in another thread. - The upper limit for the interval value is determined by the number - of milliseconds that can be specified in a signed integer - (in practice, this is a period of just over 24 days). The accuracy - depends on the underlying operating system. Windows 2000 has 15 - millisecond accuracy; other systems that we have tested can handle - 1 millisecond intervals. - - The main API for the timer functionality is QTimer. That class - provides regular timers that emit a signal when the timer fires, and - inherits QObject so that it fits well into the ownership structure - of most Qt programs. The normal way of using it is like this: - - \snippet timers/timers.cpp 0 - \snippet timers/timers.cpp 1 - \snippet timers/timers.cpp 2 - - The QTimer object is made into a child of \c this object so that, - when \c this object is deleted, the timer is deleted too. - Next, its \l{QTimer::}{timeout()} signal is connected to the slot - that will do the work, it is started with a value of 1000 - milliseconds, indicating that it will time out every second. - - QTimer also provides a static function for single-shot timers. + The main API for the timer functionality was \l QTimer. QTimer stores + the interval in a signed integer, which limits the maximum interval it + supports to the number of milliseconds that can fit in a signed integer + (in practice, this is a period of around 24 days). + + Qt 6.8 introduced the \l QChronoTimer class to replace QTimer. QChronoTimer + stores the interval as \c std::chrono::nanoseconds, which means that + the maximum interval it supports is around 292 years. This mitigates + the chances of integer overflow that QTimer had if the interval was more + than \c{std::numeric_limits<int>::max()}. + + The accuracy of the timers depends on the underlying operating system. + Windows 2000 has 15ms accuracy; other systems that we have tested can + handle 1ms intervals. + + QChronoTimer provides regular timers that emit a signal when the timer + fires, and inherits from QObject so that it fits well into the ownership + structure of most Qt programs. The normal way of using it is like this: + + \snippet timers/timers.cpp timer-interval-in-ctor + \snippet timers/timers.cpp timer-setinterval + + The QChronoTimer object is made into a child of the \c this object so + that, when \c this is destroyed, the timer is destroyed too. Next, the + \l{QChronoTimer::}{timeout()} signal is connected to the slot that will + do the work, the timer interval can be either passed to the constructor, + or set later on with setInterval(). + + QChronoTimer also provides static functions for single-shot timers. For example: - \snippet timers/timers.cpp 3 + \snippet timers/timers.cpp qchronotimer-singleshot - 200 milliseconds (0.2 seconds) after this line of code is - executed, the \c updateCaption() slot will be called. + 200ms after this line of code is executed, the \c updateCaption() slot + will be called. - For QTimer to work, you must have an event loop in your - application; that is, you must call QCoreApplication::exec() - somewhere. Timer events will be delivered only while the event - loop is running. + For QChronoTimer to work, you must have an event loop in your application; + that is, you must call QCoreApplication::exec() somewhere. Timer events + will be delivered only while the event loop is running. - 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 timer's - \l{QObject::thread()}{thread affinity} to determine which thread - will emit the \l{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. - - The \l{widgets/analogclock}{Analog Clock} example shows how to use - QTimer to redraw a widget at regular intervals. From \c{AnalogClock}'s - implementation: - - \snippet timers/analogclock.cpp 0 - \snippet timers/analogclock.cpp 2 - \snippet timers/analogclock.cpp 3 - \snippet timers/analogclock.cpp 4 - \snippet timers/analogclock.cpp 5 - \snippet timers/analogclock.cpp 6 - \dots - \snippet timers/analogclock.cpp 7 - - Every second, QTimer will call the QWidget::update() slot to + In multithreaded applications, you can use QChronoTimer 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 \l{QObject::thread()}{thread affinity} + to determine which thread will emit the \l{QChronoTimer::}{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. + + The \l{widgets/analogclock}{Analog Clock} example shows how to + use QChronoTimer to redraw a widget at regular intervals. From + \c{AnalogClock}'s implementation: + + \snippet timers/analogclock.cpp analogclock-qchronotimer + + Every second, QChronoTimer will call the QWidget::update() slot to refresh the clock's display. If you already have a QObject subclass and want an easy optimization, you can use QBasicTimer instead of QTimer. With QBasicTimer, you must reimplement \l{QObject::timerEvent()}{timerEvent()} in your QObject subclass - and handle the timeout there. The \l{widgets/wiggly}{Wiggly} - example shows how to use QBasicTimer. + and handle the timeout there. */ |