Как получить текущее местоположение, используя отдельный класс в Android

Я обновил класс выше чистым способом.

public class LocationHandler implements LocationListener,
        GoogleApiClient.ConnectionCallbacks,
        GoogleApiClient.OnConnectionFailedListener {
    private Context mContext;
    private GoogleApiClient mGoogleApiClient;
    private LocationRequest mLocationRequest;
    private OnLocationUpdateListener onLocationUpdateListener;

    public LocationHandler(Context mContext) {
        this.mContext = mContext;
        buildGoogleApiClient();
        createLocationRequest();
    }

    protected synchronized void buildGoogleApiClient() {
        mGoogleApiClient = new GoogleApiClient.Builder(mContext)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .addApi(LocationServices.API)
                .build();
        mGoogleApiClient.connect();
    }

    public void startLocationUpdates(Context mContext) {
        if (ActivityCompat.checkSelfPermission(mContext,
                Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED
                && ActivityCompat.checkSelfPermission(mContext,
                Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            return;
        }
        LocationServices.FusedLocationApi.requestLocationUpdates(
                mGoogleApiClient, mLocationRequest, this);
    }

    private void stopLocationUpdate(Context mContext) {
        LocationServices.FusedLocationApi.removeLocationUpdates(
                mGoogleApiClient, this);
    }

    //other new Methods but not using right now..
    protected void createLocationRequest() {
        mLocationRequest = new LocationRequest();
        mLocationRequest.setInterval(10000);//set the interval in which you want to get locations
        mLocationRequest.setFastestInterval(5000);//if a location is available sooner you can get it (i.e. another app is using the location services)
        mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
    }

    @Override
    public void onConnected(@Nullable Bundle bundle) {
        startLocationUpdates(mContext);
    }

    @Override
    public void onConnectionSuspended(int i) {
    }

    @Override
    public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
    }

    @Override
    public void onLocationChanged(Location location) {
        if(mGoogleApiClient.isConnected() && onLocationUpdateListener != null){
            onLocationUpdateListener.onLocationChange(location);
        }
    }

    public void setOnLocationUpdateListener(OnLocationUpdateListener onLocationUpdateListener) {
        this.onLocationUpdateListener = onLocationUpdateListener;
    }
}

где OnLocationUpdateListener — это

public interface OnLocationUpdateListener {
    void onLocationChange(Location location);
    void onError(EnumUtil.ErrorType errorType);
}

Для запуска события onConnected требуется некоторое время. Вы должны дать ему немного времени, прежде чем делать тосты. Я бы добавил свойство isConnected в ваш класс LocationHandler следующим образом:

private boolean isconnected = false;

public boolean isConnected() {
    return isconnected;
}

@Override
public void onConnected(Bundle bundle) {
    mLastLocation = LocationServices.FusedLocationApi.getLastLocation(
            mGoogleApiClient);
    if (mLastLocation != null) {
        latitude =String.valueOf(mLastLocation.getLatitude());
        longitude = String.valueOf(mLastLocation.getLongitude());
    }
    this.isconnected = true;
}

Затем в MainActivity

LocationHandler appLocationManager = new LocationHandler(HomeActivity.this);

while(!appLocationManager.isConnected()) {
// wait for a bit
}

if (appLocationManager.isConnected()) {
    Toast.makeText(getApplicationContext(), appLocationManager.getLatitude().toString(), Toast.LENGTH_SHORT).show();
    Toast.makeText(getApplicationContext(), appLocationManager.getLongitude().toString(), Toast.LENGTH_SHORT).show();
}

Вы должны установить значение широты и долготы с помощью установщика, а затем получить использование геттера.. поскольку значение не устанавливается, геттер возвращает нулевое значение, таким образом, исключение нулевого указателя.

Вот еще одно решение с FusedLocationProviderClient, поскольку FusedLocationApi устарело.

    public class LocationHandler {
    private Activity activity;
    private FusedLocationProviderClient mFusedLocationProviderClient;
    private Location mLastKnownLocation;
    private LocationCallback mLocationCallback;
    private LocationRequest mLocationRequest;
    private OnLocationUpdateListener onLocationUpdateListener;
    private boolean updateStartedInternally = false;

    public LocationHandler(Activity activity, OnLocationUpdateListener onLocationUpdateListener) {
        this.activity = activity;
        this.onLocationUpdateListener = onLocationUpdateListener;
        mFusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(activity);
        createLocationRequest();
        getDeviceLocation();

        mLocationCallback = new LocationCallback() {
            @Override
            public void onLocationResult(LocationResult locationResult) {
                List<Location> locationList = locationResult.getLocations();
                if (locationList.size() > 0) {
                    //The last location in the list is the newest
                    Location location = locationList.get(locationList.size() - 1);
                    mLastKnownLocation = location;
                    if (onLocationUpdateListener != null) {
                        onLocationUpdateListener.onLocationChange(location);
                        if(updateStartedInternally){
                            stopLocationUpdate();
                        }
                    }
                }
            }
        };
    }

    private void getDeviceLocation() {
        /*
         * Get the best and most recent location of the device, which may be null in rare
         * cases when a location is not available.
         */
        try {
            Task locationResult = mFusedLocationProviderClient.getLastLocation();
            locationResult.addOnCompleteListener(activity, task -> {
                if (task.isSuccessful()) {
                    // Set the map's camera position to the current location of the device.
                    mLastKnownLocation = (Location) task.getResult();
                    if (mLastKnownLocation == null) {
                        updateStartedInternally = true;
                        mFusedLocationProviderClient.requestLocationUpdates(mLocationRequest, mLocationCallback, Looper.myLooper());
                    } else {
                        onLocationUpdateListener.onLocationChange(mLastKnownLocation);
                    }
                } else {
                    onLocationUpdateListener.onError("Can't get Location");
                }
            });
        } catch (SecurityException e) {
            Log.e("Exception: %s", e.getMessage());
            onLocationUpdateListener.onError(e.getMessage());

        }
    }

    public void startLocationUpdates() {
        if (ActivityCompat.checkSelfPermission(activity, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(activity, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            return;
        }
        updateStartedInternally = false;
        mFusedLocationProviderClient.requestLocationUpdates(mLocationRequest, mLocationCallback, Looper.myLooper());
    }

    private void stopLocationUpdate() {
        mFusedLocationProviderClient.removeLocationUpdates(mLocationCallback);
    }


    //other new Methods but not using right now..
    protected void createLocationRequest() {
        mLocationRequest = new LocationRequest();
        mLocationRequest.setInterval(10000);//set the interval in which you want to get locations
        mLocationRequest.setFastestInterval(5000);//if a location is available sooner you can get it (i.e. another app is using the location services)
        mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
    }
}

где OnLocationUpdateListener

public interface OnLocationUpdateListener {
    void onLocationChange(Location location);
    void onError(String error);
}