Google Maps移动摄像头不起作用-为什么？

Question

此活动是获取当前用户位置并每10秒更新一次，问题是：

mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(latLng, 20));

不起作用，地图显示如下

，如果我将此行移到onCreate，则应用程序崩溃并显示错误消息：

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.gms.maps.GoogleMap.moveCamera(com.google.android.gms.maps.CameraUpdate)' on a null object reference
        at com.ENG.Activities.Maps.UserLocation.onCreate(UserLocation.java:56)

我应该怎么做才能打开地图并缩放到我的位置？

UserLocationActivity

public class UserLocation extends AppCompatActivity implements OnMapReadyCallback,
    LocationListener, GoogleApiClient.OnConnectionFailedListener, GoogleApiClient.ConnectionCallbacks {

private GoogleMap mMap;
private GoogleApiClient mGoogleApiClient;
private FusedLocationProviderClient fusedLocationClient;
private LocationRequest mLocationRequest;
private Location mLastLocation;
private LatLng latLng;
private double lat, lng;
private Marker mCurrentUserLocationMarker;
private final int UPDATE_LOCATION_TIME = 10000;
private final int FASTEST_LOCATION_TIME = 5000;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_user_location);

    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map_current_location);
    mapFragment.getMapAsync(this);

    fusedLocationClient = LocationServices.getFusedLocationProviderClient(this);
}

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

    mGoogleApiClient.connect();
}

private synchronized void buildLocationRequest() {
    mLocationRequest = LocationRequest.create();
    mLocationRequest.setInterval(UPDATE_LOCATION_TIME)
            .setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY)
            .setFastestInterval(FASTEST_LOCATION_TIME);
}

@Override
public void onMapReady(GoogleMap googleMap) {
    this.mMap = googleMap;

    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
        return;
    }
    buildGoogleApiClient();
    mMap.setMyLocationEnabled(true);
}

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

@Override
public void onConnectionSuspended(int i) {
    buildGoogleApiClient();
}

@Override
public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
    Toast.makeText(getApplicationContext(), "Failed to connect", Toast.LENGTH_LONG).show();
    buildGoogleApiClient();
}

@Override
public void onLocationChanged(Location location) {
    this.mLastLocation = location;

    if (mCurrentUserLocationMarker != null) {
        mCurrentUserLocationMarker.remove();
    }

    lat = mLastLocation.getLatitude();
    lng = mLastLocation.getLongitude();
    latLng = new LatLng(lat, lng);
    MarkerOptions markerOptions = new MarkerOptions();
    markerOptions.position(latLng)
            .title("Current user Location")
            .icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_AZURE));

    mCurrentUserLocationMarker = mMap.addMarker(markerOptions);

    mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(latLng, 20));
}

}

Answer 1

您确定您的onLocationUpdate函数已执行吗？

从您的moveCamera函数调用onCreate时出现a行是很正常的，因为Camera对象尚不存在。它仅在执行onMapReady时存在。