Acquiring a cached location value in WRT

From Forum Nokia Wiki

ID		Creation date	October 15th, 2009
Platform	S60 5th Edition, S60 3rd FP2	Tested on devices	Nokia N97, Nokia N97 Mini
Category	Web Runtime (WRT)	Subcategory	Platform Services

Keywords (APIs, classes, methods, functions): location javascript

Overview

Latest S60 devices incorporate a small but valuable addition to JavaScript Location Service API.

"Last known position" information is useful for getting a quick response from the location API on where the last positioning fix was acquired.

As a developer, you might want to first check if this cached value is available and ask the user if he's happy with the estimate, before requesting a new location fix from the framework.

I put together some sample code to assist you in integrating this feature to your widget.

The beef

Set up the location service object and call:

var result = locAPI.ILocation.GetLastPosition();

If the returned error code is 0, you can use the freshly acquired cached location data:

if (result.ErrorCode == 0){
   var posObject = result.ReturnValue;
   myLogger(posObject.Latitude + ' - ' + posObject.Longitude); 					
}

If the "last known position" feature is supported, but no cached data is available:

else if (result.ErrorCode == 1014){
   myLogger('Last known position data is not available');
}

...and finally, if your user is sporting old SW, that does not support this feature

else{
   myLogger('ErrorCode: ' + result.ErrorCode + '<br/>' + 'ErrorMessage: ' + result.ErrorMessage);
}

Devices that currently incorporate this feature

N97 20.0.019 and later N97 Mini 10.0.020 and later

Full example code

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
	<head>
		<title> Sample Widget</title>
		<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
		<script language="javascript" type="text/javascript" src="basic.js"></script>
    	<link rel="stylesheet" href="basic.css" type="text/css">
    	<META NAME="Generator" CONTENT="Nokia WRT plug-in for Aptana Studio 2.2.0" />
 
		<script>
			var locAPI = null;	
			function init(){
				locAPI = device.getServiceObject("Service.Location", "ILocation");
			}
 
			function getLastKnownPosition(){
 
				if(!locAPI)
					init();
 
				// Here's the fancy (but hidden) API call
				var result = locAPI.ILocation.GetLastPosition();
 
				// Yey, we can use the cached location info!
				if (result.ErrorCode == 0){
					var posObject = result.ReturnValue;
					myLogger(posObject.Latitude + ' - ' + posObject.Longitude); 					
				}
 
				// Last known position data is not available
				else if (result.ErrorCode == 1014){
					myLogger('Last known position data is not available');
				}
 
				// Hmpf, this SW version does not support last known position API
				else{
					myLogger('ErrorCode: ' + result.ErrorCode + '<br/>' + 'ErrorMessage: ' + result.ErrorMessage);
				}								
			}
 
			function myLogger(txt){
				document.getElementById("myconsole").innerHTML = txt;
			}
 
		</script>
 
	</head>
	<body onload="init();">
		<div><a style="font-size:1.5em" id="actionjackson" href="#" onclick="getLastKnownPosition();">Last known position</a></div>
		<div id="myconsole"></div>
	</body>
</html>

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