问刷新许多Google标记位置，而不刷新Android中的整个地图

EN

 public void update(Observable observable, final Object object)
 {

     if (observable instanceof ListPositions && object != null)
     {        
         Position p = (Position) object;
         LatLng position = new LatLng(p.getLatitude(), p.getLongitude());
         // Where i'd like to move the markers

     }
     else
     {
        // Where i'd like to remove the marker from the map
     }
 }

public class ListPositions extends Observable{

private HashMap<String,Position> mapPosition;

private ListPositions()
{
    mapPosition = new HashMap<String, Position>();
    VehicleMapFragment mapFragmentObserver = new VehicleMapFragment();
    this.addObserver(mapFragmentObserver);
}


private static ListPositions INSTANCE = null;


public static synchronized ListPositions getInstance()
{
    if (INSTANCE == null)
    { INSTANCE = new ListPositions();
    }
    return INSTANCE;
}

public int getNumberOfPosition()
{
    return mapPosition.size();
}

public void addPosition(String key, Position p){
    mapPosition.put(key,p);
    setChanged();
    notifyObservers(p);
}

public void removePosition(String key){
    mapPosition.remove(key);
    setChanged();
    notifyObservers();
}

public void onPositionMessageReceived(MqttMessage message, String source)
 {
    Gson gson = new Gson();
    String s = gson.toJson(message.toString());
    String jsonPosition = gson.toJson(message.toString());
    jsonPosition = formatMessage(jsonPosition);
    Position p = gson.fromJson(jsonPosition, Position.class);

    ListPositions.getInstance().addPosition(source, p);


}

public void update(Observable observable, final Object object)
{
    if (observable instanceof ListPositions && object != null)
    {
        Position p = (Position) object;

        position = new LatLng(p.getLatitude(), p.getLongitude());
        options = new MarkerOptions().position(position).title("TEST").snippet("TEST");

        PositionUpdate positionUpdaterTask = new PositionUpdate(myGoogleMap, options, position);
    positionUpdaterTask.execute();
    }
}

public class PositionUpdate extends AsyncTask<Void, Void, Void>{

private GoogleMap myGoogleMap;
private MarkerOptions options;
private LatLng positionToAdd;


public PositionUpdate(GoogleMap googleMap, MarkerOptions options, LatLng position)
{
    this.myGoogleMap = googleMap;
    this.options = options;
    this.positionToAdd = position;
}


@Override
protected Void doInBackground(Void...voids)
{
    return null;
}

@Override
protected void onPostExecute(Void aVoid)
{
    if (myGoogleMap != null)
    {
        myGoogleMap.addMarker(options.position(positionToAdd));
        Log.i(ConstElisa.LOG_ELISA, "MARKER ADDED");
    }
    else
    {
        Log.e(ConstElisa.LOG_ELISA, "ERROR ADDING THE MARKER");
    }

    super.onPostExecute(aVoid);
}