1 <?xml version="1.0" encoding="utf-8"?>

     2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

     3 <!-- This component and the accompanying materials are made available under the terms of the License 

     4 "Eclipse Public License v1.0" which accompanies this distribution, 

     5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

     6 <!-- Initial Contributors:

     7     Nokia Corporation - initial contribution.

     8 Contributors: 

     9 -->

    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-E5B5C3CA-B256-5B29-AB90-590676444C85" xml:lang="en"><title>How

    13 to start a periodic timer</title><shortdesc>Provides code snippets to show you how to start a periodic timer</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    14 <p>A periodic timer, <codeph>CPeriodic</codeph>, invokes a function at regular

    15 intervals. You must wrap the function to be called in a <codeph>TCallBack</codeph>. </p>

    16 <p>First, we provide a callback function for the timer to call. The callback

    17 function can be a static member, i.e. <codeph>TInt X::Foo(TAny *)</codeph> or

    18 global, i.e. <codeph>TInt Foo(TAny *)</codeph>. The <codeph>TAny*</codeph> can

    19 point to any object that we specify when we start the timer.</p>

    20 <p>It is awkward to deal with <codeph>TAny*</codeph>, and more convenient

    21 to write handler code from a non-static member function, so here we code a

    22 static function to invoke a non-static function <codeph>DoTick()</codeph> as

    23 follows:</p>

    24 <codeblock id="GUID-8D673BE4-1F28-58E0-868D-98B48DD91C60" xml:space="preserve">TInt CPeriodicRunner::Tick(TAny* aObject)

    25     {

    26     // cast, and call non-static function

    27     ((CPeriodicRunner*)aObject)->DoTick();

    28     return 1;

    29     }

    30 </codeblock>

    31 <p>The next piece of code creates a <codeph>CPeriodic</codeph> and sets it

    32 off with one-second ticks. The callback is specified to call the static <codeph>Tick()</codeph> function,

    33 passing the <codeph>this</codeph> pointer (which we use in <codeph>Tick()</codeph> to

    34 call <codeph>DoTick()</codeph>).</p>

    35 <codeblock id="GUID-092F13DD-9158-5245-A1FE-101EFB305D15" xml:space="preserve">void CPeriodicRunner::StartTimer()

    36     {

    37     const TInt tickInterval=1000000;

    38     iPeriodic=CPeriodic::NewL(0); // neutral priority

    39     iPeriodic->StartInMicroSeconds(tickInterval,tickInterval,TCallBack(Tick, this));

    40     }

    41 </codeblock>

    42 </conbody></concept>