Question

I’m having some troubles trying to display the main Activity in Android. The problems started when the Activity extends MapView (I don’t know why). The LogCat shows some errors but I dont know what they mean. Here is the LogCat:

03-07 05:42:56.859: D/AndroidRuntime(15357): Shutting down VM
03-07 05:42:56.859: W/dalvikvm(15357): threadid=1: thread exiting with uncaught exception (group=0x40018578)
03-07 05:42:56.859: E/AndroidRuntime(15357): FATAL EXCEPTION: main
03-07 05:42:56.859: E/AndroidRuntime(15357): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.geo.location/com.geo.location.GeoLocationActivity}: java.lang.IllegalArgumentException: listener==null
03-07 05:42:56.859: E/AndroidRuntime(15357):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
03-07 05:42:56.859: E/AndroidRuntime(15357):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
03-07 05:42:56.859: E/AndroidRuntime(15357):    at android.app.ActivityThread.access$1500(ActivityThread.java:117)
03-07 05:42:56.859: E/AndroidRuntime(15357):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
03-07 05:42:56.859: E/AndroidRuntime(15357):    at android.os.Handler.dispatchMessage(Handler.java:99)
03-07 05:42:56.859: E/AndroidRuntime(15357):    at android.os.Looper.loop(Looper.java:130)
03-07 05:42:56.859: E/AndroidRuntime(15357):    at android.app.ActivityThread.main(ActivityThread.java:3687)
03-07 05:42:56.859: E/AndroidRuntime(15357):    at java.lang.reflect.Method.invokeNative(Native Method)
03-07 05:42:56.859: E/AndroidRuntime(15357):    at java.lang.reflect.Method.invoke(Method.java:507)
03-07 05:42:56.859: E/AndroidRuntime(15357):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
03-07 05:42:56.859: E/AndroidRuntime(15357):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
03-07 05:42:56.859: E/AndroidRuntime(15357):    at dalvik.system.NativeStart.main(Native Method)
03-07 05:42:56.859: E/AndroidRuntime(15357): Caused by: java.lang.IllegalArgumentException: listener==null
03-07 05:42:56.859: E/AndroidRuntime(15357):    at android.location.LocationManager.requestLocationUpdates(LocationManager.java:444)
03-07 05:42:56.859: E/AndroidRuntime(15357):    at com.geo.location.GeoLocationActivity.onCreate(GeoLocationActivity.java:64)
03-07 05:42:56.859: E/AndroidRuntime(15357):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
03-07 05:42:56.859: E/AndroidRuntime(15357):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
03-07 05:42:56.859: E/AndroidRuntime(15357):    ... 11 more

And this is the code of the app.

public class GeoLocationActivity extends MapActivity implements LocationListener {
    private TextView lblLatitud; 
    private TextView lblLongitud;
    private TextView lblPrecision;
    private TextView lblEstado;
    private TextView lblVelocidad;
    private DecimalFormat df;
    private MapView lblMapView; 
    private MapController mapController; 
    private LocationManager locManager;
    private LocationListener locListener;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        df = new DecimalFormat("#.########");
        lblLatitud = (TextView) findViewById(R.id.LblPosLatitud);
        lblLongitud = (TextView) findViewById(R.id.LblPosLongitud);
        lblPrecision = (TextView) findViewById(R.id.LblPosPrecision);
        lblVelocidad = (TextView) findViewById(R.id.LblV);
        lblEstado = (TextView) findViewById(R.id.textView8);
        lblPrecision = (TextView) findViewById(R.id.LblPosPrecision);
        lblMapView  = (MapView) findViewById(R.id.mapview);
        lblMapView.setBuiltInZoomControls(true);

        lblLatitud.setText("");
        lblLongitud.setText("");
        lblPrecision.setText("");
        lblVelocidad.setText("");
        lblEstado.setText("");
        lblPrecision.setText("");

        locManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
        //Obtenemos la última posición conocida
        Location loc = locManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
        //Mostramos la última posición conocida
        mostrarPosicion(loc);
        locManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locListener);

    }

    //Rellena los TextView de la Activity con la información básica de la posición
    private void mostrarPosicion(Location loc) {
        if(loc != null){
            lblLatitud.setText(String.valueOf(df.format(loc.getLatitude())));
            lblLongitud.setText(String.valueOf(df.format(loc.getLongitude())));
            lblPrecision.setText(String.valueOf(loc.getAccuracy())+ " metros");
            lblEstado.setText("GPS Ok");
            lblVelocidad.setText(String.valueOf(loc.getSpeed()*(3600/1000)) + "km/h <=> " + String.valueOf(loc.getSpeed()) + "m/s"); 
        }else{
            lblLatitud.setText("(sin_datos)");
            lblLongitud.setText("(sin_datos)");
            lblEstado.setText("(GPS no disponible)");
            lblPrecision.setText("(sin_datos)");
            lblVelocidad.setText("(sin_datos)");
        }
    }

    @Override
    protected boolean isRouteDisplayed() {
        return false;
    }

    //Añade un punto al array y muestra la posicion en el mapa
    protected void updateLocation(Location location) {
        GeoPoint point = new GeoPoint((int)(location.getLatitude() * 1E6), (int)(location.getLongitude() * 1E6));   
        mapController = lblMapView.getController();
        mapController.animateTo(point);
        mapController.setZoom(lblMapView.getMaxZoomLevel());    
        List<Overlay> mapOverlays = lblMapView.getOverlays();
        MiOverlay2 marker = new MiOverlay2(point, this);
        mapOverlays.add(marker);
        lblMapView.invalidate();
    }

    public void onLocationChanged(Location location) {
        lblEstado.setText("Gps Ok");
        mostrarPosicion(location);
        updateLocation(location);
    }
    public void onProviderDisabled(String provider){
        lblEstado.setText("No connection");
        Intent intent = new Intent(android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS);
        startActivity(intent);
    }
    public void onProviderEnabled(String provider){
        lblEstado.setText("Gps Ok");
    }
    public void onStatusChanged(String provider, int status, Bundle extras){
        Log.i("", "Provider Status: " + status);
    }
}


 /***********************************************************************
 * CLASS:                                                               *
 * OVERLAY QUE PINTA LAS FLECHAS EN LUGAR DONDE ESTA SITUADO EL USUARIO *
 ***********************************************************************/
class MiOverlay extends Overlay { 
    GeoPoint punto; 
    Context ctxt; 

    public MiOverlay (GeoPoint punto, Context ctxt) {
        super();
        this.punto = punto;
        this.ctxt = ctxt; 
    }

    @Override
    public boolean draw(Canvas canvas, MapView mapView, boolean shadow, long when) {
        super.draw(canvas, mapView, shadow);

       //se traduce el punto geo localizado a un punto en la pantalla
       Point scrnPoint = new Point();
       mapView.getProjection().toPixels(punto, scrnPoint);

       //se construye un bitmap a partir de la imagen
       Bitmap marker = BitmapFactory.decodeResource(ctxt.getResources() , R.drawable.arrow);

       //se dibuja la imagen del marker
       canvas.drawBitmap(marker,
               scrnPoint.x - marker.getWidth() / 2,
               scrnPoint.y - marker.getHeight(), 
               null);
       return true;
    }
} 

As you can see, it’s a very simple program, but I can’t find out the problem.

Answer 1

The LocationListener, locListener, is never initialized, and is therefore null…

locManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locListener);