Question

all. I am writing an android app about GPS locations.

I tried it on emulator and entered the latitude and longitude manually, and it worked fine.
However, my problem is: on the real device, in debugging mode, to go the next class by using intent can only be achieved when location is changed. If I start the app directly, I can see the blinking GPS icon, but the app will only stay here, and won’t start the next activity. It seems that the variables in the onLocationChanged() will never be changed.

I have heard that to get the location instantly is to use the getLastKnownLocation() method. But I failed to get where I should use it.

Here is the class of how I use the LocationManager to get the locations.

Is there any solutions? I am quite confused. Thank you very much!!

    public class mainMenu extends Activity{

private LocationManager locationManager = null;

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




    Button button1 = (Button)findViewById(R.id.button1);
    button1.setOnClickListener(new OnClickListener(){
        public void onClick(View v){

            Intent i3 = new Intent();
            i3.setClass(mainMenu.this, police.class);
            i3.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
            mainMenu.this.startActivityForResult(i3,0);


        }
    });

    Button button2 = (Button)findViewById(R.id.button2);
    button2.setOnClickListener(new OnClickListener(){
        public void onClick(View v){

            Intent i3 = new Intent();
            i3.setClass(mainMenu.this, ambulance.class);
            i3.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
            mainMenu.this.startActivityForResult(i3,0);


        }
    });

    Button button3 = (Button)findViewById(R.id.button3);
    button3.setOnClickListener(new OnClickListener(){
        public void onClick(View v){

            Intent i3 = new Intent();
            i3.setClass(mainMenu.this, fire_station.class);
            i3.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
            mainMenu.this.startActivityForResult(i3,0);


        }
    });



        locationManager = (LocationManager)mainMenu.this.getSystemService(Context.LOCATION_SERVICE);

        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 120000 , 0, new MyLocationUpdater());

        String provider = LocationManager.GPS_PROVIDER;
        Location location = locationManager.getLastKnownLocation(provider);



}



public class MyLocationUpdater implements LocationListener{ //change location interface
    @Override
    public void onLocationChanged(Location location) {
        // TODO Auto-generated method stub
    //          store the location data
    //          get the best record



        Double lat = location.getLatitude();
        Double lon = location.getLongitude();

        System.out.println("The latitude is " + lat + "and " 
                + "the longitude is "+ lon);


        Double lat11 = lat - 1/69.0;
        Double lat12 = lat + 1/69.0;
        Double lon11 = lon - 1/42.0;
        Double lon12 = lon + 1/42.0;

        StaticVariables.latS1 = lat11.toString();
        StaticVariables.latN1 = lat12.toString();
        StaticVariables.lonW1 = lon11.toString();
        StaticVariables.lonE1 = lon12.toString();

        Double lat111 = lat - 2/69.0;
        Double lat121 = lat + 2/69.0;
        Double lon111 = lon - 2/42.0;
        Double lon121 = lon + 2/42.0;

        StaticVariables.latS11 = lat111.toString();
        StaticVariables.latN11 = lat121.toString();
        StaticVariables.lonW11 = lon111.toString();
        StaticVariables.lonE11 = lon121.toString();

    //          ==================================================
    //          ambulances

        Double lat21 = lat - 3/69.0;
        Double lat22 = lat + 3/69.0;
        Double lon21 = lon - 3/42.0;
        Double lon22 = lon + 3/42.0;

        StaticVariables.latS2 = lat21.toString();
        StaticVariables.latN2 = lat22.toString();
        StaticVariables.lonW2 = lon21.toString();
        StaticVariables.lonE2 = lon22.toString();

        Double lat211 = lat - 5.5/69.0;
        Double lat221 = lat + 5.5/69.0;
        Double lon211 = lon - 5.5/42.0;
        Double lon221 = lon + 5.5/42.0;

        StaticVariables.latS21 = lat211.toString();
        StaticVariables.latN21 = lat221.toString();
        StaticVariables.lonW21 = lon211.toString();
        StaticVariables.lonE21 = lon221.toString();

    //          ===================================================
    //          fire stations

        Double lat31 = lat - 2/69.0;
        Double lat32 = lat + 2/69.0;
        Double lon31 = lon - 2/42.0;
        Double lon32 = lon + 2/42.0;

        StaticVariables.latS3 = lat31.toString();
        StaticVariables.latN3 = lat32.toString();
        StaticVariables.lonW3 = lon31.toString();
        StaticVariables.lonE3 = lon32.toString();

        Double lat311 = lat - 2/69.0;
        Double lat321 = lat + 2/69.0;
        Double lon311 = lon - 2/42.0;
        Double lon321 = lon + 2/42.0;

        StaticVariables.latS31 = lat311.toString();
        StaticVariables.latN31 = lat321.toString();
        StaticVariables.lonW31 = lon311.toString();
        StaticVariables.lonE31 = lon321.toString();

        Intent intent = new Intent();
        intent.setClass(mainMenu.this, getPhoneNumber.class);
        mainMenu.this.startActivity(intent);
    }

    @Override
    public void onProviderDisabled(String arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onProviderEnabled(String arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onStatusChanged(String arg0, int arg1, Bundle arg2) {
        // TODO Auto-generated method stub

    }
}

    }

Answer 1

The getLastKnownLocation method does not trigger an onLocationChanged event. One way to refactor your code would be to move the logic that acts on a Location to a separate method and then call that method both after you call getLastKnownLocation, and from your onLocationChanged method.

Bear in mind that there is no guarantee that getLastKnownLocation will provide a meaningful Location, since you the device might have moved since the last location update.

Example code:

public void onCreate(Bundle savedInstanceState){
    ....
    String provider = LocationManager.GPS_PROVIDER;
    Location location = locationManager.getLastKnownLocation(provider);
    updateLocation(location);
}

public class MyLocationUpdater implements LocationListener{ //change location interface
    @Override
    public void onLocationChanged(Location location) {
        updateLocation(location);
    }
    ...
}

void updateLocation(Location location) {
    Double lat = location.getLatitude();
    Double lon = location.getLongitude();

    // the rest of the code from onLocationChanged
}