Android-从另一个类的oncreate（）获取变量

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);

Answer 1

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 .

Answer 2

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.