update UI when a variable from other Classes is changed

Question

I have an offline-map App which uses GPS-Tracker. My primary goal is to sense changes in latitude and longitude and update a TextView.
My GPS-Tracker class is implemented as follows:

public class GPSTracker extends Service implements LocationListener {

    ...

    public GPSTracker(Context context) {
        ...
        getLocation();
    }

    public Location getLocation() {
        // returns Location
    }

    @Override
    public void onLocationChanged(Location location) {
        // Method 1: update UI elements (textview) directly 
        MainActivity.tvGPS.setText("lat: " + Double.toString(location.getLatitude()) + "lon: " + Double.toString(location.getLongitude());

        // Method 2: call a method from MainActivity which updates UI
        MainActivity.setNewPosition(location.getLatitude() , location.getLatitude());

        // Method 3: sense changes in Latitude and Longitude directly in MainActivity and update UI
    }
}

Question:
How can I directly sense changes of Latitude and Longitude (in MainActivity) and modify UI.
what I so far tested:

UI update from GPSTracker/onLocationChanged (as Method 1 and 2 in the code): It works but it is not from MainActivity

using LocalBroacastManager as mentioned here but it demands constantly checking of location to detect changes

using Observer Pattern as mentioned here: changes are sensible only in Observer Class not in MainActivity

Check my answer here : http://stackoverflow.com/a/36665760/4706693 In your case, you'd send the broadcast in the `onLocationChanged()` for example — NSimon, Apr 22 '16 at 12:07

score 0 · Answer 1 · answered Apr 22 '16 at 12:14

0

You could pass the MainActivity as a parameter in the constructor of GPSTracker.

private TextView tvGPS;

public GPSTracker(Activity a) {
      ...
      tvGPS = (TextView)a.findViewById(R.id.tvGPS); // whatever ID
}

Then you could change the text directly in onLocationChanged.

@Override
public void onLocationChanged(Location location) {
    tvGPS.setText("lat: " + Double.toString(location.getLatitude()) + "lon: " + Double.toString(location.getLongitude());
}

answered Apr 22 '16 at 12:14

user0815

213
2
11

Is it more or less the same as defining a public TextView which is accessible from other classes? this concept would increase the complexity, especially when UI-update from several classes is demanded. – Behy Apr 22 '16 at 12:32

score 0 · Answer 2 · answered Apr 22 '16 at 12:48

Please, don't pass Activity instance into tracker with static methods usage! This is very bad practice!

You can use event bus. http://square.github.io/otto/

Create a bus provider :

public class BusProvider {
    private static final Bus BUS = new Bus(ThreadEnforcer.ANY);

    public static Bus getInstance() {
        return BUS;
    }

    private BusProvider() {
        // No instances.
    }
}

Create a bus event:

     public class LocationChangedEvent{

    private Location location;

      private Location location;

        public LocationChangedEvent(Location location) {
            this.location = location;
        }

        public Location getLocation() {
            return location;
        }

        public void setLocation(Location location) {
            this.location = location;
        }
 }



public class GPSTracker extends Service implements LocationListener {

        ...

    public GPSTracker(Context context) {
        ...
        getLocation(); 
    }

    public Location getLocation() {
        // returns Location
    }

    @Override
    public void onLocationChanged(Location location) {
       new Handler(Looper.getMainLooper()).post(new Runnable() {
                @Override
                public void run() {
                    BusProvider.getInstance().post(new LocationChangedEvent(location));
                }
            });
    }
}

inside your activity:

 @Subscribe
    public void onLocationUpdated(LocationChangedEvent locationChangedEvent){
        //TODO update ui as you need

    }

Don't forget to register/ unregister bus

update UI when a variable from other Classes is changed

2 Answers2