Need help, GeolocationEvent.UPDATE does not fire?

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Flex

Hi,
I am developing a small app in felx mobile project for blackberry playbook, am using flash builder burrito,
i want to get the current location's latitude ,longtitude value using GPS. But the geolocation event does not fire in my code, anyother way to get the latitude,longtitude value?

protected function button1_clickHandler(event:MouseEvent):void
            {
                // TODO Auto-generated method stub

                if(Geolocation.isSupported)
                {
                        txt_GPS.text = "GPS Supported";
                        geocode.setRequestedUpdateInterval(100);
                        geocode.addEventListener(GeolocationEvent.UPDATE,handleLocationRequest);

                }
                else
                {
                    txt_GPS.text = "Not Supported";
                }

            }

            public function handleLocationRequest(event:GeolocationEvent):void
            {
                txt_GPS.text = event.latitude.toString();
            }