Name
QTimer - Timer signals and single-shot timers
Synopsis
Qt 5 continues to support the old string-based syntax for connecting signals and slots defined in a QObject or any class that inherits from QObject (including QWidget) connect (sender, SIGNAL (valueChanged (QString, QString)), receiver, SLOT (updateValue (QString))); New: connecting to QObject member. The following example shows how to use a QTimer to call a slot every 1 second. In the example, we use a QProgressBar to update its value and check the timer is working properly.
#include <qtimer.h>
Inherits QObject.
Public Members
- void timeout ()
Static Public Members
This can be used to do heavy work while providing a snappy user interface:myObject->processOneThing() will be called repeatedly and should return quickly (typically after processing one data item) so that Qt can deliver eventsto 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; multi-threadingis now becoming available on more and more platforms, and we expect that null events will eventually be replaced by threading.
Note that QTimer's accuracy depends on the underlying operating system and hardware. Most platforms support an accuracy of 20ms; some provide more. If Qt isunable 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 (whichmust, of course, inherit QObject). The disadvantage is that timerEvent() does not support such high-level features as single-shot timers or signals.
Some operating systems limit the number of timers that may be used; Qt tries to work around these limitations.
See also Event Classes and Time and Date.
Member Function Documentation
QTimer::QTimer ( QObject * parent = 0, const char * name = 0 )
Constructs a timer called name, with the parent parent.
Note that the parent object's destructor will destroy this timer object.
QTimer::~QTimer ()
Destroys the timer.
void QTimer::changeInterval ( int msec )
Changes the timeout interval to msec milliseconds.
If the timer signal is pending, it will be stopped and restarted; otherwise it will be started.
See also start() and isActive().
bool QTimer::isActive () const
Returns TRUE if the timer is running (pending); otherwise returns FALSE.
Example: t11/cannon.cpp.
void QTimer::singleShot ( int msec, QObject * receiver, const char * member ) [static]
This static function calls a slot after a given time interval.
It is very convenient to use this function because you do not need to bother with a timerEvent or to create a local QTimer object.
Example:This sample program automatically terminates after 10 minutes (i.e. 600000 milliseconds).
The receiver is the receiving object and the member is the slot. The time interval is msec.
int QTimer::start ( int msec, bool sshot = FALSE )
Starts the timer with a msec milliseconds timeout, and returns the ID of the timer, or zero when starting the timer failed.
If sshot is TRUE, the timer will be activated only once; otherwise it will continue until it is stopped.
Any pending timer will be stopped.
See also singleShot(), stop(), changeInterval(), and isActive().
Examples:
void QTimer::stop ()
Stops the timer.
See also start().
Examples:
void QTimer::timeout () [signal]
This signal is emitted when the timer is activated.
Examples:
int QTimer::timerId () const
Returns the ID of the timer if the timer is running; otherwise returns -1.
See Also
Copyright
Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com. See the license file included in the distribution for a complete licensestatement.
Author
Generated automatically from the source code.
Bugs
If you find a bug in Qt, please report it as described in http://doc.trolltech.com/bughowto.html. Good bug reports help us to help you. Thank you.
Qt Qtimer Signal Slot Adapter
The definitive Qt documentation is provided in HTML format; it is located at $QTDIR/doc/html and can be read using Qt Assistant or with a web browser. Thisman page is provided as a convenience for those users who prefer man pages, although this format is not officially supported by Trolltech.
Qt Qtimer Signal Slot Machine
If you find errors in this manual page, please report them to [email protected]. Please include the name of the manual page (qtimer.3qt) and theQt version (3.3.8).