我想在从Firebase实时数据库中检索位置的地图活动中添加标记。

我尝试在addChildEventListener()和onCreate()方法中实现OnmapReady()，并且当用户登录时，尽管没有错误，但它们都不起作用，我还使用logcat来显示位置坐标，但其值未显示。

    email = PreferenceManager.getDefaultSharedPreferences(getBaseContext()).getString("email","");
    password = PreferenceManager.getDefaultSharedPreferences(getBaseContext()).getString("password","");
    name = PreferenceManager.getDefaultSharedPreferences(getBaseContext()).getString("name","");
    gender = PreferenceManager.getDefaultSharedPreferences(getBaseContext()).getString("gender","");
    age = PreferenceManager.getDefaultSharedPreferences(getBaseContext()).getString("age","");
    mobileNumber = PreferenceManager.getDefaultSharedPreferences(getBaseContext()).getString("mobileNumber","");
    if (email == "" || password == "" || name == "" || mobileNumber == "" || age == "" || gender == "") {
        startactivity(new Intent(this,Welcomeactivity.class));
        return;
    }

    setContentView(R.layout.activity_maps);
    getSupportactionBar().setTitle(R.string.app_name);

    firebaseAuth = FirebaseAuth.getInstance();
    firebaseSignIn();

    MobileAds.initialize(this,"ca-app-pub-3940256099942544~3347511713");
    rewardedVideoAd = MobileAds.getRewardedVideoAdInstance(this);
    rewardedVideoAd.setRewardedVideoAdListener(this);
    rewardedVideoAd.loadAd("ca-app-pub-3940256099942544/5224354917",new AdRequest.Builder().build());

    MobileAds.initialize(this,"ca-app-pub-3940256099942544~3347511713");
    adView = findViewById(R.id.adView);
    AdRequest adRequest = new AdRequest.Builder().build();
    adView.loadAd(adRequest);

    findNurseButton = findViewById(R.id.find_nurse);
    findNurseButton.setOnClicklistener(new View.OnClicklistener() {
        @Override
        public void onClick(View v) {
            findNurseButton.setText("finding nearby nurses");

        }
    });

    // Obtain the SupportMapFragment and get notified when the map is ready to be used.
    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
    assert mapFragment != null;
    mapFragment.getMapAsync(this);

    getLocationPermission();
    createLocationRequest();
    mFusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(this);

    locationCallback = new LocationCallback() {
        @Override
        public void onLocationResult(LocationResult locationResult) {
            if (locationResult == null) {
                return;
            }
            else {
                try {
                    for (Location location : locationResult.getLocations()) {
                        // Update UI with location data
                        // ...
                        sendNurseRequest();
                        lastLocation = location;
                        LatLng latLng = new LatLng(location.getLatitude(),location.getLongitude());
                        mMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
                        mMap.animateCamera(CameraUpdateFactory.zoomTo(16f));
                        Log.i("location updates: ","latitude: " + location.getLatitude() + ",longitude: " + location.getLongitude());
                        userReference.child("auth id").setvalue(userID);
                        userReference.child("latitude").setvalue(location.getLatitude());
                        userReference.child("longitude").setvalue(location.getLongitude());
                    }
                }
                catch (NullPointerException e) {

                }
            }
        }
    };
    mFusedLocationProviderClient.requestLocationUpdates(locationRequest,locationCallback,Looper.getMainLooper());

    DatabaseReference nurseRef = FirebaseDatabase.getInstance().getReference().child("nurses available/2");
    nurseRef.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(@NonNull Datasnapshot datasnapshot,@Nullable String s) {
            LatLng latLng = new LatLng(Double.parseDouble(datasnapshot.child("latitude").getvalue().toString()),Double.parseDouble(datasnapshot.child("longitude").getvalue().toString()));
            mMap.addMarker(new MarkerOptions().position(latLng));
            Log.i("latslongs ","firebase latitude:" + datasnapshot.child("latitude").getvalue() + "firebase longitude" + datasnapshot.child("longitude").getvalue());
        }

        @Override
        public void onChildChanged(@NonNull Datasnapshot datasnapshot,"firebase latitude:" + datasnapshot.child("latitude").getvalue() + "firebase longitude" + datasnapshot.child("longitude").getvalue());

        }

        @Override
        public void onChildRemoved(@NonNull Datasnapshot datasnapshot) {

        }

        @Override
        public void onChildmoved(@NonNull Datasnapshot datasnapshot,"firebase latitude:" + datasnapshot.child("latitude").getvalue() + "firebase longitude" + datasnapshot.child("longitude").getvalue());
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {
            Log.e("database error",databaseError.getMessage());
        }
    });
}

/**
 * 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;
   mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
    if (locationPermissionGranted && checkinternet()) {
        getDeviceLocation();
    }
}

这是我的数据库