Android - Get variable from oncreate() of another class

Question

I have a class GetMyLocation that gets the current location of the user. Now I'm trying to call an object of this class from another class, ShowMap2. But I am unable to send the updated location to the new class.

I haven't included the other overrides for GetMyLocation here.

What I have:

public class ShowMap2 extends Activity{
        @Override
        protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_showmap);

        GetMyLocation myLocation = new GetMyLocation();


        myLat = myLocation.GetCurrentLat();
        myLon = myLocation.GetCurrentLon();

   }

This is the class that gets the location:

public class GetMyLocation extends Activity implements LocationListener {


    protected LocationManager locationManager;
    protected LocationListener locationListener;
    Location location;

    public static double myLat, myLon;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this);

        location = locationManager.getLastKnownLocation(locationManager.GPS_PROVIDER);


       this.myLat = location.getLatitude();
       this.myLon = location.getLongitude();

    }


    public double GetCurrentLat(){
        return this.myLat;
    }

    public double GetCurrentLon(){
        return this.myLon;
    }

The above code returns 0.0 for both lat and lon.

I have tried every possible way I could think of, but I always end up get 0.0. I know the class itself gets my current lat and lon, but I am not able to pass it correctly. Could some please help me out here?

Thanks.

PS:

I found this thread, and tried it accordingly, but to no avail. Still zeros.

How to access this variable from an Android onCreate method?

The only difference, in the question in the link, the class is static. When I make my class static, it says: Modifier 'static' not allowed here.

My updated code:

public class GetMyLocation extends Activity implements LocationListener {

    protected LocationManager locationManager;
    protected LocationListener locationListener;
    Location location;

    static double myLat, myLon;

    double GetCurrentLat(){
        return myLat;
    }

    double GetCurrentLon(){
        return myLon;
    }


    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this);

        location = locationManager.getLastKnownLocation(locationManager.GPS_PROVIDER);

        this.myLat = location.getLongitude();
        this.myLon = location.getLongitude();

    }

EDIT: Updated Code that works:

public class GetMyLocation implements LocationListener {
//public class GetMyLocation extends Activity implements LocationListener {

    private static final LatLng HAMBURG = new LatLng(43.48484521,-80.5274279);
    private GoogleMap map;

    protected LocationManager locationManager;
    protected LocationListener locationListener;
    Location location;

    private static double myLat, myLon;

    GetMyLocation(Activity activity){

        locationManager = (LocationManager) activity.getSystemService(Context.LOCATION_SERVICE);
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this);

        location = locationManager.getLastKnownLocation(locationManager.GPS_PROVIDER);

        this.myLat = location.getLatitude();
        this.myLon = location.getLongitude();

    }

    double GetCurrentLat(){
        return this.myLat;
    }

    double GetCurrentLon(){
        return this.myLon;
    }

getting the location values from ShowMap2 using:

GetMyLocation myLocation = new GetMyLocation(this);

simply instantiation a class GetMyLocation myLocation = new GetMyLocation(); does not call methods on it `onCreate(Bundle savedInstanceState);' You need to learn how to create a new Activity — Scary Wombat
– Scary Wombat, Commented Feb 27, 2015 at 5:29

MeetTitan · Accepted Answer · 2015-02-28 03:32:18Z

0

You're extending Activity in GetMyLocation. For the goal you want, remove extends Activity, and move the code from onCreate() to a suitable constructor such as GetMyLocation().

The rest of your logic is solid.

An activity is for GUI, and if you don't intend on opening a new activity with your class, don't extend Activity. For the code to work from onCreate(), you'd have to create an intent of your class, and start the activity, which would open a blank activity, because you're not setting any views in GetMyLocation.

In layman's terms, your onCreate() is never called because you're never starting the activity.

EDIT To pass a Context to our class so it runs correctly, we will define our constructor like so:

GetMyLocation(Context context) {
    locationManager = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);
    locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this);

    location = locationManager.getLastKnownLocation(locationManager.GPS_PROVIDER);

    this.myLat = location.getLatitude();
    this.myLon = location.getLongitude();

}

And we will initialize our class like so: GetMyLocation location = new GetMyLocation(this); from within your Activity. When we reference this from our class, it points to that class, which just so happens to be an Activity satisfying our GetMyLocation(Context context) constructor. Then you can call your methods and get the expected results.

When you originally called getSystemService() you implied this which was a reference to your activity that was never started. That's also why your IDE got mad at you when you removed extends Activity from GetMyLocation(). It didn't know where to look for for getSystemService(), because the implied class this was no longer a Context.

edited Feb 28, 2015 at 3:32

answered Feb 27, 2015 at 5:31

MeetTitan

3,5851 gold badge16 silver badges31 bronze badges

Sign up to request clarification or add additional context in comments.

10 Comments

fractal5 Over a year ago

If I remove extend Activity, it cannot resolve getSystemService. Also I had previously moved the code from onCreate() to a contructor. But that would make the app close/crash when I ran it.

MeetTitan Over a year ago

Then you must pass a Context as a parameter in your constructor. I'll add an example snippet to my answer.

fractal5 Over a year ago

That works well, thanks. Just one question, what is the Context that I should be passing from my ShowMap2 class. This is my first app in Java, so I'm sort of lost.

MeetTitan Over a year ago

@fractal5, Context is what Activity extends, and getSystemService() is a method of Context. You can replace Context with Activity and in your instance, it will run exactly the same with no errors. Every Activity is a Context, but every Context is not an Activity. Just like every cat is an animal, but every animal is not a cat. If this concept doesn't make sense, google java inheritance and take a look at some of the documentation. Oh and if you feel I've helped you feel free to upvote or accept the answer.

MeetTitan Over a year ago

@fractal5, also think of animals eating. All animals eat, but not every animal necessarily eats the same thing, or the same way. This is akin to inherited methods.

|

Bob · Accepted Answer · 2015-02-27 05:59:13Z

-1

If you want to pass parameters from Activity to Activity, use Bundle. If you want to get result when Activity is exiting, use startActivityForRestult when creating the new Activity. If you just want to pass parameters from Activity to another class, use the class's constructor.

answered Feb 27, 2015 at 5:59

Bob

345 bronze badges

Collectives™ on Stack Overflow

Android - Get variable from oncreate() of another class

2 Answers 2

10 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

10 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related