diff options
| author | Timothy Pearson <kb9vqf@pearsoncomputing.net> | 2011-07-10 15:24:15 -0500 |
|---|---|---|
| committer | Timothy Pearson <kb9vqf@pearsoncomputing.net> | 2011-07-10 15:24:15 -0500 |
| commit | bd0f3345a938b35ce6a12f6150373b0955b8dd12 (patch) | |
| tree | 7a520322212d48ebcb9fbe1087e7fca28b76185c /doc/html/timers.html | |
| download | qt3-bd0f3345a938b35ce6a12f6150373b0955b8dd12.tar.gz qt3-bd0f3345a938b35ce6a12f6150373b0955b8dd12.zip | |
Add Qt3 development HEAD version
Diffstat (limited to 'doc/html/timers.html')
| -rw-r--r-- | doc/html/timers.html | 152 |
1 files changed, 152 insertions, 0 deletions
diff --git a/doc/html/timers.html b/doc/html/timers.html new file mode 100644 index 0000000..eff5bb9 --- /dev/null +++ b/doc/html/timers.html @@ -0,0 +1,152 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> +<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/object.doc:86 --> +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> +<title>Timers</title> +<style type="text/css"><!-- +fn { margin-left: 1cm; text-indent: -1cm; } +a:link { color: #004faf; text-decoration: none } +a:visited { color: #672967; text-decoration: none } +body { background: #ffffff; color: black; } +--></style> +</head> +<body> + +<table border="0" cellpadding="0" cellspacing="0" width="100%"> +<tr bgcolor="#E5E5E5"> +<td valign=center> + <a href="index.html"> +<font color="#004faf">Home</font></a> + | <a href="classes.html"> +<font color="#004faf">All Classes</font></a> + | <a href="mainclasses.html"> +<font color="#004faf">Main Classes</font></a> + | <a href="annotated.html"> +<font color="#004faf">Annotated</font></a> + | <a href="groups.html"> +<font color="#004faf">Grouped Classes</font></a> + | <a href="functions.html"> +<font color="#004faf">Functions</font></a> +</td> +<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>Timers</h1> + + + +<p> <a href="qobject.html">QObject</a>, the base class of all Qt objects, provides the basic timer +support in Qt. With <a href="qobject.html#startTimer">QObject::startTimer</a>(), you start a timer with +an <em>interval</em> in milliseconds as argument. The function returns a +unique integer timer id. The timer will now "fire" every <em>interval</em> +milliseconds, until you explicitly call <a href="qobject.html#killTimer">QObject::killTimer</a>() with +the timer id. +<p> For this mechanism to work, the application must run in an event +loop. You start an event loop with <a href="qapplication.html#exec">QApplication::exec</a>(). When a +timer fires, the application sends a <a href="qtimerevent.html">QTimerEvent</a>, 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. +<p> There is practically no upper limit for the interval value (more than +one year is possible). The accuracy depends on the underlying operating +system. Windows 95/98 has 55 millisecond (18.2 times per second) +accuracy; other systems that we have tested (UNIX X11 and Windows NT) +can handle 1 millisecond intervals. +<p> The main API for the timer functionality is <a href="qtimer.html">QTimer</a>. That class +provides regular timers that emit a signal when the timer fires, and +inherits <a href="qobject.html">QObject</a> so that it fits well into the ownership structure +of most GUI programs. The normal way of using it is like this: +<pre> + <a href="qtimer.html">QTimer</a> * counter = new <a href="qtimer.html">QTimer</a>( this ); + connect( counter, SIGNAL(<a href="qtimer.html#timeout">timeout</a>()), + this, SLOT(updateCaption()) ); + counter-><a href="qtimer.html#start">start</a>( 1000 ); +</pre> + +<p> The counter timer is made into a child of this widget, so that when +this widget is deleted, the timer is deleted too. Next, its timeout +signal is connected to the slot that will do the work, and finally +it's started. +<p> <a href="qtimer.html">QTimer</a> also provides a simple one-shot timer API. <a href="qbutton.html">QButton</a> uses this +to show the button being pressed down and then (0.1 seconds later) be +released when the keyboard is used to "press" a button, for example: +<p> <pre> + QTimer::<a href="qtimer.html#singleShot">singleShot</a>( 100, this, SLOT(animateTimeout()) ); +</pre> + +<p> 0.1 seconds after this line of code is executed, the same button's +animateTimeout() slot is called. +<p> Here is an outline of a slightly longer example that combines object +communication via signals and slots with a QTimer object. It +demonstrates how to use timers to perform intensive calculations in a +single-threaded application without blocking the user interface. +<p> <pre> + // The Mandelbrot class uses a QTimer to calculate the mandelbrot + // set one scanline at a time without blocking the CPU. It + // inherits QObject to use signals and slots. Calling start() + // starts the calculation. The done() signal is emitted when it + // has finished. Note that this example is not complete, just an + // outline. + + class Mandelbrot : public <a href="qobject.html">QObject</a> + { + <a href="metaobjects.html#Q_OBJECT">Q_OBJECT</a> // required for signals/slots + public: + Mandelbrot( <a href="qobject.html">QObject</a> *parent=0, const char *name ); + ... + public slots: + void start(); + signals: + void done(); + private slots: + void calculate(); + private: + <a href="qtimer.html">QTimer</a> timer; + ... + }; + + // + // Constructs and initializes a Mandelbrot object. + // + + Mandelbrot::Mandelbrot( <a href="qobject.html">QObject</a> *parent=0, const char *name ) + : <a href="qobject.html">QObject</a>( parent, name ) + { + <a href="qobject.html#connect">connect</a>( &timer, SIGNAL(<a href="qtimer.html#timeout">timeout</a>()), SLOT(calculate()) ); + ... + } + + // + // Starts the calculation task. The internal calculate() slot + // will be activated every 10 milliseconds. + // + + void Mandelbrot::start() + { + if ( !timer.<a href="qtimer.html#isActive">isActive</a>() ) // not already running + timer.<a href="qtimer.html#start">start</a>( 10 ); // timeout every 10 ms + } + + // + // Calculates one scanline at a time. + // Emits the done() signal when finished. + // + + void Mandelbrot::calculate() + { + ... // perform the calculation for a scanline + if ( finished ) { // no more scanlines + timer.<a href="qtimer.html#stop">stop</a>(); + emit done(); + } + } + </pre> + +<p> +<!-- eof --> +<p><address><hr><div align=center> +<table width=100% cellspacing=0 border=0><tr> +<td>Copyright © 2007 +<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a> +<td align=right><div align=right>Qt 3.3.8</div> +</table></div></address></body> +</html> |