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diff --git a/src/corelib/doc/src/timers.qdoc b/src/corelib/doc/src/timers.qdoc new file mode 100644 index 0000000000..eddb600559 --- /dev/null +++ b/src/corelib/doc/src/timers.qdoc @@ -0,0 +1,123 @@ +/**************************************************************************** +** +** Copyright (C) 2012 Digia Plc and/or its subsidiary(-ies). +** Contact: http://www.qt-project.org/legal +** +** 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 Digia. For licensing terms and +** conditions see http://qt.digia.com/licensing. For further information +** use the contact form at http://qt.digia.com/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: http://www.gnu.org/copyleft/fdl.html. +** $QT_END_LICENSE$ +** +****************************************************************************/ + +/*! + \page timers.html + \title Timers + \brief How to use Qt timers in your application. + + \ingroup best-practices + + 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 + regular intervals until you explicitly call QObject::killTimer() + with the 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 + 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 + busy doing something else. In other words: the accuracy of timers + depends on the granularity of your application. + + In multithreaded applications, you can use the timer mechanism in + any thread that has an event loop. To start an event loop from a + non-GUI thread, use QThread::exec(). Qt uses the object's + \l{QObject::thread()}{thread affinity} to determine which thread + will deliver the QTimerEvent. Because of this, you must start and + 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 GUI 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 this widget so that, + when this widget 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. + For example: + + \snippet timers/timers.cpp 3 + + 200 milliseconds (0.2 seconds) 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. + + 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 analogclock.cpp 0 + \snippet analogclock.cpp 2 + \snippet analogclock.cpp 3 + \snippet analogclock.cpp 4 + \snippet analogclock.cpp 5 + \snippet analogclock.cpp 6 + \dots + \snippet analogclock.cpp 7 + + Every second, QTimer 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. +*/ |