无法使用唯一密钥从Firebase检索用户位置数据

Question

我检查了我的另一个应用程序，该应用程序从实时数据库中检索位置，用户的位置根本不反映在地图上。我一直在代码中配置数据库引用，以获得用户位置的正确路径，但应用程序一直因NullPointerExceptions而崩溃。我应该如何引用正确的子键，尤其是用户的唯一键？

代码如下：

private GoogleMap mMap;
private ActivityRetrieveMapsBinding binding;
private Location mLocation;
private LocationManager mLocationManager;
private LocationRequest mLocationRequest;
private com.google.android.gms.location.LocationListener listener;
private LocationManager locationManager;
GoogleApiClient mGoogleApiClient;
public static final int REQUEST_CHECK_SETTINGS = 1001;
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    binding = ActivityRetrieveMapsBinding.inflate(getLayoutInflater());
    setContentView(binding.getRoot());

    // 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);

    mLocationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
    checkLocation();
    if (mGoogleApiClient == null) {
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .addConnectionCallbacks((GoogleApiClient.ConnectionCallbacks) this)
                .addOnConnectionFailedListener((GoogleApiClient.OnConnectionFailedListener) this)
                .addApi(LocationServices.API)
                .build();
    }

    mGoogleApiClient.connect();

    LocationRequest mLocationRequest = new LocationRequest();
    mLocationRequest.setInterval(10000);
    mLocationRequest.setFastestInterval(5000);
    mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);

    LocationSettingsRequest.Builder builder = new LocationSettingsRequest.Builder()
            .addLocationRequest(mLocationRequest);

    PendingResult<LocationSettingsResult> result =
            LocationServices.SettingsApi.checkLocationSettings(mGoogleApiClient, builder.build());

    result.setResultCallback(new ResultCallback<LocationSettingsResult>() {
        @Override
        public void onResult(@NonNull LocationSettingsResult locationSettingsResult) {

            final Status status = locationSettingsResult.getStatus();
            final LocationSettingsStates LS_state = locationSettingsResult.getLocationSettingsStates();
            switch (status.getStatusCode()) {
                case LocationSettingsStatusCodes.SUCCESS:
                    // All location settings are satisfied. The client can initialize location
                    // requests here.

                    break;
                case LocationSettingsStatusCodes.RESOLUTION_REQUIRED:
                    // Location settings are not satisfied. But could be fixed by showing the user
                    // a dialog.
                    try {
                        // Show the dialog by calling startResolutionForResult(),
                        // and check the result in onActivityResult().
                        status.startResolutionForResult(RetrieveMapsActivity.this, REQUEST_CHECK_SETTINGS);

                    } catch (IntentSender.SendIntentException e) {
                        // Ignore the error.
                    }
                    break;
                case LocationSettingsStatusCodes.SETTINGS_CHANGE_UNAVAILABLE:
                    // Location settings are not satisfied. However, we have no way to fix the
                    // settings so we won't show the dialog.

                    break;
            }
        }
    });
}

private boolean checkLocation() {

    if(!isLocationEnabled()){
        showAlert();
    }
    return isLocationEnabled();

}



private void showAlert() {
    final AlertDialog.Builder dialog = new AlertDialog.Builder(this);
    dialog.setTitle("Enable Location")
            .setMessage("Your Locations Settings is set to 'Off'.\nPlease Enable Location to " +
                    "use this app")
            .setPositiveButton("Location Settings", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface paramDialogInterface, int paramInt) {

                    Intent myIntent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
                    startActivity(myIntent);
                }
            })
            .setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface paramDialogInterface, int paramInt) {

                }
            });
    dialog.show();
}

private boolean isLocationEnabled() {

    locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
    return locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER) ||
            locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
}

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

    DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
    DatabaseReference locationkey = reference.child("Users").child(uid).child("User Location");

    locationkey.addValueEventListener(new ValueEventListener () {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            for (DataSnapshot dataSnapshot : snapshot.getChildren()) {

                String locationKey = dataSnapshot.getKey();
                LocationSend send = snapshot.getValue(LocationSend.class);
                LatLng location = new LatLng(send.latitude, send.longitude);
                mMap.addMarker(new MarkerOptions()
                        .position(location)
                        .title(getCompleteAddress(send.latitude, send.longitude)));
                mMap.moveCamera(CameraUpdateFactory.newLatLng(location));
                mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(location,14F));
            }
        }


        @Override
        public void onCancelled(@NonNull DatabaseError error) {
            Log.d(TAG, error.getMessage());
        }
    });



}



private String getCompleteAddress(double Latitude,double Longitude){

    String address = "";

    Geocoder geocoder = new Geocoder(RetrieveMapsActivity.this, Locale.getDefault());

    try{

        List<Address> addresses = geocoder.getFromLocation(Latitude,Longitude,1);

        if(address!=null){

            Address returnAddress = addresses.get(0);
            StringBuilder stringBuilderReturnAddress =  new StringBuilder("");

            for(int i=0; i<=returnAddress.getMaxAddressLineIndex();i++){
                stringBuilderReturnAddress.append(returnAddress.getAddressLine(i)).append("\n");
            }

            address = stringBuilderReturnAddress.toString();

        }
        else{
            Toast.makeText(this, "Address not found", Toast.LENGTH_SHORT).show();
        }

    }
    catch (Exception e){
        Toast.makeText(this, e.getMessage(), Toast.LENGTH_SHORT).show();
    }


    return address;
}


@Override
public void onLocationChanged(@NonNull Location location) {

}

@Override
public void onConnected(@Nullable Bundle bundle) {

}

@Override
public void onConnectionSuspended(int i) {

}

@Override
public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {

}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    final LocationSettingsStates states = LocationSettingsStates.fromIntent(data);
    if (requestCode == REQUEST_CHECK_SETTINGS) {
        switch (resultCode) {
            case Activity.RESULT_OK:
                // All required changes were successfully made

                break;
            case Activity.RESULT_CANCELED:
                // The user was asked to change settings but chose not to

                break;
            default:
                break;
        }
    }
}

}

Answer 1

使用以下引用时：

String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference uidRef = rootRef.child("Users").child(uid).child("User Location");

请注意，没有必要遍历结果。您只应再次对DataSnapshot对象调用.child()，如下代码行所示：

uidRef.get().addOnCompleteListener(new OnCompleteListener<DataSnapshot>() {
    @Override
    public void onComplete(@NonNull Task<DataSnapshot> task) {
        if (task.isSuccessful()) {
            DataSnapshot snapshot = task.getResult();
            double latitude = snapshot.child("latitude").getValue(Double.class);
            double longitude = snapshot.child("longitude").getValue(Double.class);
            Log.d("TAG", "latitude, longitude");
        } else {
            Log.d("TAG", task.getException().getMessage()); //Don't ignore potential errors!
        }
    }
});

logcat中的结果将是：

15.44318, 120.7148767