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</script><link href="../PRODUCT_PLUGIN/book.css" rel="stylesheet" type="text/css"/><link href="css/s60/style.css" rel="stylesheet" type="text/css" media="all"/></head><body onload="initPage();"><div class="body"><div class="contentLeft prTxt"><h1 class="pageHeading" id="GUID-7A0190CB-545E-48D2-BAF0-D28E03CDFCA5"><span>ILocation.</span>Trace()</h1><div>
<p><strong>Description:</strong></p>
<p>The <code>Trace</code> method retrieves periodic updates about
the current location of the device based on a predefined update interval.</p>
<p>This is an asynchronous method.</p>
<p><strong>Syntax:</strong></p>
<pre class="codeblock" id="GUID-676491ED-F5F1-4B9C-887C-EB50FE523F99">result = so.ILocation.Trace(criteria, callback);</pre>
<p><strong>Arguments:</strong></p>
<ul>
<li><p><code>criteria</code>:</p>
<p>This is an object that specifies what type of device location information
is returned and how. For more information about the object properties and
how to define them, see section <a href="GUID-4541E532-CC1A-4115-8467-7FA1C4378307.html#GUID-4541E532-CC1A-4115-8467-7FA1C4378307">Criteria for retrieving location information</a>.</p>
</li>
<li><p><code>callback</code>:</p>
<p>The <code>callback</code> argument is the name of the method
that is executed when <code>Trace</code> has results or status information
to return. You must define this method separately. Follow the instructions
in section <a href="GUID-C7C3B541-8D28-4DC6-9003-ECF57F26C608.html#GUID-C7C3B541-8D28-4DC6-9003-ECF57F26C608">Defining the callback handler for an asynchronous method</a> to
define the <code>callback</code> method.</p>
</li>
</ul>
<p><strong>Return value:</strong></p>
<p>The <code>Trace</code> method returns an object that contains
the initial return value for the asynchronous call it started (see the following
table). The actual location information is returned by the <a href="GUID-C7C3B541-8D28-4DC6-9003-ECF57F26C608.html#GUID-C7C3B541-8D28-4DC6-9003-ECF57F26C608"><code>callback</code></a> method in the <code>ReturnValue</code> property of its result object.
The returned information is described in section <a href="GUID-A6C9AF19-6694-478B-A9FE-7898A2091C4B.html#GUID-A6C9AF19-6694-478B-A9FE-7898A2091C4B">Returned location information</a>.</p>
<div class="tablenoborder"><a name="GUID-F2F7057D-0C4F-4837-9567-ACA408CEA101"><!----></a><table cellpadding="4" cellspacing="0" summary="" id="GUID-F2F7057D-0C4F-4837-9567-ACA408CEA101" frame="border" border="1" rules="all"><caption><strong>Table: </strong>Return value
properties for Trace</caption>
<thead align="left">
<tr class="title "><th class="cellrowborder" valign="top" width="33.33333333333333%" id="d0e48640">
<p>Property</p>
</th><th class="cellrowborder" valign="top" width="33.33333333333333%" id="d0e48645">
<p>Description</p>
</th><th class="cellrowborder" valign="top" width="33.33333333333333%" id="d0e48650">
<p>Value</p>
</th></tr>
</thead>
<tbody>
<tr class="">
<td class="cellrowborder" valign="top" width="33.33333333333333%" headers="d0e48640 ">
<p><code>result.TransactionID</code></p>
</td>
<td class="cellrowborder" valign="top" width="33.33333333333333%" headers="d0e48645 ">
<p>This is a number used as an identification to match transactions started
with the <code>Trace</code> call to one or more calls it generates
to <code>callback</code>.</p>
</td>
<td class="cellrowborder" valign="top" width="33.33333333333333%" headers="d0e48650 "> </td>
</tr>
<tr class="bg ">
<td class="cellrowborder" valign="top" width="33.33333333333333%" headers="d0e48640 ">
<p><code>result.ErrorCode</code></p>
</td>
<td class="cellrowborder" valign="top" width="33.33333333333333%" headers="d0e48645 ">
<p>This is a number that specifies a predefined error code.</p>
</td>
<td class="cellrowborder" valign="top" width="33.33333333333333%" headers="d0e48650 ">
<p>See <a href="GUID-0A215AF3-59F0-4158-842C-0D7B030E5EA4.html#GUID-0A215AF3-59F0-4158-842C-0D7B030E5EA4">Service API error codes</a>.</p>
</td>
</tr>
<tr class="">
<td class="cellrowborder" valign="top" width="33.33333333333333%" headers="d0e48640 ">
<p><code>result.ErrorMessage</code></p>
</td>
<td class="cellrowborder" valign="top" width="33.33333333333333%" headers="d0e48645 ">
<p>This is a text string that describes the error.</p>
</td>
<td class="cellrowborder" valign="top" width="33.33333333333333%" headers="d0e48650 ">
<p>See <a href="GUID-DEA4164E-5F03-4B57-97B9-4C6238481F89.html#GUID-DEA4164E-5F03-4B57-97B9-4C6238481F89">Location Service API error messages</a>.</p>
</td>
</tr>
</tbody>
</table></div>
<p><strong>Remarks:</strong></p>
<ul>
<li><p><code>Trace</code> retrieves location updates until
cancelled with <a href="GUID-7A466B60-88DD-4A3A-B64C-E7300D42DA56.html#GUID-7A466B60-88DD-4A3A-B64C-E7300D42DA56"><code>CancelNotification</code></a>.
You can therefore have only one <code>Trace</code> call (one instance)
pending or in use at any given time.</p></li>
<li><p>The availability of specific location information depends
on the underlying GPS technology. Other factors, such as the number of satellites
available for a location fix, also affect what information can be returned.
You can change the positioning system used by an S60 device from the <strong>Settings
> General > Positioning > Positioning methods</strong> menu.</p></li>
<li><p>It takes time to retrieve the initial position fix. Subsequent
requests are faster.</p></li>
</ul>
<p><strong>Example code:</strong></p>
<p/>
<p>For the complete source of a sample widget
that demonstrates how to use this Service API, see <a href="GUID-620340F8-F844-445E-80AA-71C757320B7E.html#GUID-620340F8-F844-445E-80AA-71C757320B7E">the
full example</a>.</p>
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