java - GPS 应用程序可以在模拟器上运行，但不能在我的手机上运行

Question

我的基本位置应用程序无法在运行 API 29 的 Galaxy A20 上运行，但在运行相同 API 的所有模拟器上运行良好。我不确定问题是什么，因为我没有使用 LOGCAT 的经验，但错误状态如下:

尝试在空对象引用上调用虚拟方法“double android.location.Location.getLatitude()”。

我的项目中的错误出现在第 117 行(最后)。但我在这里强调了它

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {

    private GoogleMap mMap;

    LocationManager locationManager;
    LocationListener locationListener;


    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);

        if (requestCode == 1){


            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED){

                if (ContextCompat.checkSelfPermission(this , Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED)

                locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER ,0 ,0 , locationListener);

            }


        }

    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_maps);
        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
    }


    /**
     * Manipulates the map once available.
     * This callback is triggered when the map is ready to be used.
     * This is where we can add markers or lines, add listeners or move the camera. In this case,
     * we just add a marker near Sydney, Australia.
     * If Google Play services is not installed on the device, the user will be prompted to install
     * it inside the SupportMapFragment. This method will only be triggered once the user has
     * installed Google Play services and returned to the app.
     */
    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;

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

        locationListener = new LocationListener() {
            @Override
            public void onLocationChanged(Location location) {


                LatLng userLocation = new LatLng(location.getLatitude(), location.getLongitude());
                mMap.clear();
                mMap.addMarker(new MarkerOptions().position(userLocation).title("Marker in user house"));
                mMap.moveCamera(CameraUpdateFactory.newLatLng(userLocation));

            }

            @Override
            public void onStatusChanged(String s, int i, Bundle bundle) {

            }

            @Override
            public void onProviderEnabled(String s) {

            }

            @Override
            public void onProviderDisabled(String s) {

            }
        };

        if (ContextCompat.checkSelfPermission(this , Manifest.permission.ACCESS_FINE_LOCATION ) != PackageManager.PERMISSION_GRANTED){

            ActivityCompat.requestPermissions(this , new String[]{Manifest.permission.ACCESS_FINE_LOCATION} , 1);

        }
        else{

            locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER , 0 , 0 , locationListener);

            Location lastKnownLocation = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);

            LatLng userLocation = new LatLng(lastKnownLocation.getLatitude(), lastKnownLocation.getLongitude()); // ◅ THE ERROR OCCOURS HERE********
            mMap.clear();
            mMap.addMarker(new MarkerOptions().position(userLocation).title("Marker in user house"));
            mMap.moveCamera(CameraUpdateFactory.newLatLng(userLocation));


        }



    }
}

Answer 1

也许您的手机尚未成功修复 GPS。使用前检查 lastKnowLocation 是否为 null，并在手机可以“看到”天空的外部测试应用程序。