<?xml version="1.0" encoding="utf-8"?>+
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<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->+
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<!-- This component and the accompanying materials are made available under the terms of the License +
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"Eclipse Public License v1.0" which accompanies this distribution, +
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and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->+
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<!-- Initial Contributors:+
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    Nokia Corporation - initial contribution.+
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Contributors: +
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-->+
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<!DOCTYPE concept+
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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">+
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<concept id="GUID-E5B5C3CA-B256-5B29-AB90-590676444C85" xml:lang="en"><title>How+
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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>+
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<p>A periodic timer, <codeph>CPeriodic</codeph>, invokes a function at regular+
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intervals. You must wrap the function to be called in a <codeph>TCallBack</codeph>. </p>+
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<p>First, we provide a callback function for the timer to call. The callback+
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function can be a static member, i.e. <codeph>TInt X::Foo(TAny *)</codeph> or+
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global, i.e. <codeph>TInt Foo(TAny *)</codeph>. The <codeph>TAny*</codeph> can+
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point to any object that we specify when we start the timer.</p>+
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<p>It is awkward to deal with <codeph>TAny*</codeph>, and more convenient+
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to write handler code from a non-static member function, so here we code a+
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static function to invoke a non-static function <codeph>DoTick()</codeph> as+
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follows:</p>+
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<codeblock id="GUID-8D673BE4-1F28-58E0-868D-98B48DD91C60" xml:space="preserve">TInt CPeriodicRunner::Tick(TAny* aObject)+
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    {+
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    // cast, and call non-static function+
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    ((CPeriodicRunner*)aObject)-&gt;DoTick();+
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    return 1;+
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    }+
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</codeblock>+
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<p>The next piece of code creates a <codeph>CPeriodic</codeph> and sets it+
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off with one-second ticks. The callback is specified to call the static <codeph>Tick()</codeph> function,+
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passing the <codeph>this</codeph> pointer (which we use in <codeph>Tick()</codeph> to+
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call <codeph>DoTick()</codeph>).</p>+
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<codeblock id="GUID-092F13DD-9158-5245-A1FE-101EFB305D15" xml:space="preserve">void CPeriodicRunner::StartTimer()+
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    {+
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    const TInt tickInterval=1000000;+
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    iPeriodic=CPeriodic::NewL(0); // neutral priority+
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    iPeriodic-&gt;StartInMicroSeconds(tickInterval,tickInterval,TCallBack(Tick, this));+
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    }+
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</codeblock>+
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</conbody></concept>+
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