Google标记未显示

Question

在下面的代码中不显示标记。此代码是我使用预览版的Android Studio版本制作的，跟踪没有问题，但现在有了。我想制作一个带有“跟踪”标签的Google地图，因此我认为不能使用活动而只能使用片段。有人知道该怎么做吗？

return File(file.CreateReadStream(), "application/pdf");

fragment_tab2.xml

public class Tab2Map extends Fragment implements OnMapReadyCallback {
    GoogleMap mGoogleMap;
    MapView mMapView;
    View mView;

    public Tab2Map() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        mView = inflater.inflate(R.layout.fragment_tab2, container, false);
        return mView;
    }

    @Override
    public void onViewCreated(View view,Bundle savedInstanceState){
        super.onViewCreated(view,savedInstanceState);

        mMapView=(MapView) mView.findViewById(R.id.map);
        if(mMapView != null){
            mMapView.onCreate(null);
            mMapView.onResume();
            mMapView.getMapAsync(this);
        }
    }

    @Override
    public void onMapReady(GoogleMap googleMap) {
        MapsInitializer.initialize(getContext());
        mGoogleMap = googleMap;
        if (ActivityCompat.checkSelfPermission(this.getActivity(), Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this.getActivity(), Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            return;
        }
        mGoogleMap.setMyLocationEnabled(true);
        LocationManager locationManager = (LocationManager)getActivity().getSystemService(Context.LOCATION_SERVICE);
        if (ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            return;
        }
        Location location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
        LocationListener locationListener = new LocationListener() {
            public void onLocationChanged(Location location) {
                LatLng latlng = new LatLng(location.getLatitude(), location.getLongitude());
                mGoogleMap.addMarker(new MarkerOptions().position(latlng).title("Current Location").snippet(latlng.toString()));
                CameraPosition position=CameraPosition.builder().target(latlng).zoom(16).bearing(0).build();
                mGoogleMap.moveCamera(CameraUpdateFactory.newCameraPosition(position));
            }

            @Override
            public void onStatusChanged(String provider, int status, Bundle extras) {
            }

            @Override
            public void onProviderEnabled(String provider) {
            }

            @Override
            public void onProviderDisabled(String provider) {
            }
        };

        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 5, 15, locationListener);
    }
}