java - 通过 Google Maps API 获取当前位置

Question

我想要做的是在用户的当前位置上做一个标记。我收到类似的错误java.lang.NullPointerException: Attempt to invoke virtual method 'double android.location.Location.getLatitude()' on a null object reference。为什么getLatitude方法返回 null，我能做些什么来解决这个问题？谢谢你的帮助。这是我的代码：

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {

    public GoogleMap mMap;
    public Location location;

    @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);
    }

    
    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;
        // Add a marker in Sydney and move the camera

        LatLng currentLocation = new LatLng(location.getLatitude(), location.getAltitude());
        mMap.addMarker(new MarkerOptions().position(currentLocation).title("You are here"));
        mMap.moveCamera(CameraUpdateFactory.newLatLng(currentLocation));
    }
}

标签： javaandroid

Answer 1

您没有初始化位置。这就是你得到空指针异常的原因。使用此代码部分初始化位置，然后添加标记。

private double longitude;
private double latitude;
private GoogleApiClient googleApiClient;


@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);

    //Initializing googleApiClient
    googleApiClient = new GoogleApiClient.Builder(this)
            .addConnectionCallbacks(this)
            .addOnConnectionFailedListener(this)
            .addApi(LocationServices.API)
            .build();
}
private void getCurrentLocation() {
        mMap.clear();
        if (ActivityCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            // TODO: Consider calling
            //    ActivityCompat#requestPermissions
            // here to request the missing permissions, and then overriding
            //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
            //                                          int[] grantResults)
            // to handle the case where the user grants the permission. See the documentation
            // for ActivityCompat#requestPermissions for more details.
            return;
        }
        Location location = LocationServices.FusedLocationApi.getLastLocation(googleApiClient);
        if (location != null) {
            //Getting longitude and latitude
            longitude = location.getLongitude();
            latitude = location.getLatitude();

            //moving the map to location
            moveMap();
        }
    }
@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;
   

     getCurrentLocation();
   }

 private void moveMap() {
        /**
         * Creating the latlng object to store lat, long coordinates
         * adding marker to map
         * move the camera with animation
         */
        LatLng latLng = new LatLng(latitude, longitude);
        mMap.addMarker(new MarkerOptions()
                .position(latLng)
                .draggable(true)
                .title("Marker in My Location"));

        mMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
        mMap.animateCamera(CameraUpdateFactory.zoomTo(15));
        mMap.getUiSettings().setZoomControlsEnabled(true);


    }