Error in location :getLocation() method cannot be called from event thread - blackberry

Question

What I want to do is have the a map open with the click of a buttonfield with two Criterias, the user must either specify the location and then the image must be added to the location otherwise the Image must be added to the users current location.
The problem I am having is adding both criterias into an if statement in a thread / new thread or even in a FieldChangeListener.
The error I keep getting is:
Error in location :javax.microedition.location.LocationException:
getLocation() method cannot be cal[0.0] led from event thread [0.0]
Error in location :getLocation() method cannot be called from event
thread
My code:
FieldChangeListener Listener = new FieldChangeListener() {
public void fieldChanged(Field field, int context) {
ButtonField buttonClicked = (ButtonField) field;
if ((buttonClicked.getLabel()).equals("Push")) {
CustomMapField mMapField;
Coordinates mCoordinates;
BlackBerryCriteria blackBerryCriteria = null;
BlackBerryLocation blackBerryLocation = null;
BlackBerryLocationProvider blackBerryLocationProvider = null;
double Doublelat = 0.0;
double Doublelng = 0.0;
blackBerryCriteria = new BlackBerryCriteria();
if(GPSInfo.isGPSModeAvailable(GPSInfo.GPS_MODE_CELLSITE)){
blackBerryCriteria.setMode(GPSInfo.GPS_MODE_CELLSITE);
}else if(GPSInfo.isGPSModeAvailable(GPSInfo.GPS_MODE_ASSIST)){
blackBerryCriteria.setMode(GPSInfo.GPS_MODE_ASSIST);
}else if(GPSInfo.isGPSModeAvailable(GPSInfo.GPS_MODE_AUTONOMOUS)){
blackBerryCriteria.setMode(GPSInfo.GPS_MODE_AUTONOMOUS);
}else{
blackBerryCriteria.setCostAllowed(true);
blackBerryCriteria.setPreferredPowerConsumption(Criteria.POWER_USAGE_LOW);
} try {
blackBerryLocationProvider = (BlackBerryLocationProvider) BlackBerryLocationProvider.getInstance(blackBerryCriteria);
blackBerryLocation = (BlackBerryLocation) blackBerryLocationProvider.getLocation(60);
QualifiedCoordinates qualifiedCoordinates = blackBerryLocation.getQualifiedCoordinates();
Doublelat = qualifiedCoordinates.getLatitude();
Doublelng = qualifiedCoordinates.getLongitude();
mCoordinates = new Coordinates(Doublelat, Doublelng, 0);
mMapField = new CustomMapField();
mMapField.mIcon = Bitmap.getBitmapResource("coin_silver.png");
mMapField.moveTo(mCoordinates);
mMapField.setZoom(1);
add(mMapField);
}catch(Exception e){
System.out.println("Debug 5");
System.out.println("Error in location :"+e.toString());
System.out.println("Error in location :"+e.getMessage());
}
}
}
};
public class CustomMapField extends MapField {
Bitmap mIcon;
XYRect mDest;
public void moveTo(Coordinates coordinates) {
super.moveTo(coordinates);
mDest = null;
}
protected void paint(Graphics graphics) {
super.paint(graphics);
if (null != mIcon) {
if (null == mDest) {
XYPoint fieldOut = new XYPoint();
convertWorldToField(getCoordinates(), fieldOut);
int imgW = mIcon.getWidth();
int imgH = mIcon.getHeight();
mDest = new XYRect(fieldOut.x - imgW / 2,
fieldOut.y - imgH, imgW, imgH);
}
graphics.drawBitmap(mDest, mIcon, 0, 0);
}
}
}
The error Is with the following line add(mMapField);
Doublelat = qualifiedCoordinates.getLatitude();
Doublelng = qualifiedCoordinates.getLongitude();
mCoordinates = new Coordinates(Doublelat, Doublelng, 0);
mMapField = new CustomMapField();
mMapField.mIcon=Bitmap.getBitmapResource("coin_silver.png");
mMapField.moveTo(mCoordinates);
mMapField.setZoom(1);
add(mMapField);
/*MapView mapView = new MapView();
mapView.setLatitude(finalintlat);
mapView.setLongitude(finalintlng);
mapView.setZoom(10);
MapsArguments mapsArgs = new MapsArguments(mapView);
Invoke.invokeApplication(Invoke.APP_TYPE_MAPS, mapsArgs);
Please advise me more in detail how to do so, and please give an example; I can't understand how as "mMapField" is a custom MapField and "mapView" is a class Mapview (please see my code snippet above).

Answer 1

Obtaining a location is a time-consuming task, it can take as much as 1 minute even with good satellite visibility, although newer berries have improved a lot the time-to-first-fix (TTFF).
Time consuming tasks, like opening connections, or obtaining a fix, should not be performed in the event thread, because this thread has to respond to user events, and if you hog it, then the GUI frozens. And everything running inside fieldChanged runs in the event thread. So it is a good thing RIM implemented a thread detection in its new BlackBerryLocationProvider and throws exceptions, now you are aware of the bad design and can take corrective measures.
You have several options to get a fix asynchronously:
Use LocationListener.
Spawn a new thread.
Preemtively obtain a fix long before you need it (or at regular intervals), then you'll have it quickly available when the button is pressed, (either retrieving it from somewhere you previously saved it or calling LocationProvider.getLastKnownLocation).

Answer 2

You should use Invoke.invokeApplication(Invoke.APP_TYPE_MAPS, new MapsArguments(mMapField)); in place of add(mMapField);