fusedLocationProviderClient.lastLocation.addOnSuccessListener always null

问题

I just updated my Location API to use FusedLocationProviderClient but I am having this issue, when I turn off and on the GPS, I am always getting null location:

val fusedLocationProviderClient =
                        LocationServices.getFusedLocationProviderClient(callingActivity)
            fusedLocationProviderClient.flushLocations()
            getLocationRequest()

            checkLocationSettings(callingActivity, turnOnGpsRequestCode, callback) {
                // Location settings successful
                fusedLocationProviderClient.lastLocation
                        .addOnSuccessListener(callingActivity) {
                            location ->
                            // Here location is always null
callback.onCallback(MenumyRadar.RadarStatus.SUCCESS, location)
                        }
                        .addOnFailureListener {
                            callback.onCallback(MenumyRadar.RadarStatus.ERROR_UNKNOWN, null)
                        }
            }

It doesn´t work until I open another app which uses location, as Google Maps or Uber.

I have some clue thanks to this answer FusedLocationApi.getLastLocation always null

And to Google´s explanation:

fusedLocationClient.lastLocation .addOnSuccessListener { location : Location? -> // Got last known location. In some rare situations this can be null. }

The getLastLocation() method returns a Task that you can use to get a Location object with the latitude and longitude coordinates of a geographic location. The location object may be null in the following situations:

Location is turned off in the device settings. The result could be null even if the last location was previously retrieved because disabling location also clears the cache. The device never recorded its location, which could be the case of a new device or a device that has been restored to factory settings. Google Play services on the device has restarted, and there is no active Fused Location Provider client that has requested location after the services restarted. To avoid this situation you can create a new client and request location updates yourself. For more information, see Receiving Location Updates.

But it does not say how to handle this, what can I do?

回答1:

I found a solution, this is what happens, when the location is null it means the location cache was cleared, this happens when turning off GPS, so when I was turning it on there was no last location to get, what I did was this:

checkLocationSettings(callingActivity, turnOnGpsRequestCode, callback) {
                // Location settings successful
                mFusedLocationProviderClient!!.lastLocation
                        .addOnSuccessListener(callingActivity) {
                            location ->
                            if (location == null || location.accuracy > 100) {
                                mLocationCallback = object : LocationCallback() {
                                    override fun onLocationResult(locationResult: LocationResult?) {
                                        stopLocationUpdates()
                                        if (locationResult != null && locationResult.locations.isNotEmpty()) {
                                            val newLocation = locationResult.locations[0]
                                            callback.onCallback(Status.SUCCESS, newLocation)
                                        } else {
                                            callback.onCallback(Status.ERROR_LOCATION, null)
                                        }
                                    }
                                }

                                mFusedLocationProviderClient!!.requestLocationUpdates(getLocationRequest(),
                                        mLocationCallback, null)
                            } else {
                                callback.onCallback(Status.SUCCESS, location)
                            }
                        }
                        .addOnFailureListener {
                            callback.onCallback(Status.ERROR_UNKNOWN, null)
                        }
            }

When the location is null, start requesting locations using a callback and

mFusedLocationProviderClient!!.requestLocationUpdates(getLocationRequest(), mLocationCallback, null)

Then when the callback is called, a new location is got and it starts getting location again.

Sometimes it happens that when you turn on the GPS, the location is not null but the accuracy is bad, so I also check if location accuracy is good enough (For me good enough is 100 meters)

回答2:

You can use getLocationAvailability() method on your FusedLocationPrivedClient object and if it returns true then only use getLastLocation() method otherwise use requestLocationUpdates() method like this :

FusedLocationProviderClient fusedLocationProviderClient =
            LocationServices.getFusedLocationProviderClient(InitActivity.this);
    if (ActivityCompat.checkSelfPermission(this.getApplicationContext(),
            android.Manifest.permission.ACCESS_FINE_LOCATION)
            == PackageManager.PERMISSION_GRANTED) {

fusedLocationProviderClient.getLocationAvailability().addOnSuccessListener(new OnSuccessListener<LocationAvailability>() {
                @Override
                public void onSuccess(LocationAvailability locationAvailability) {
                    Log.d(TAG, "onSuccess: locationAvailability.isLocationAvailable " + locationAvailability.isLocationAvailable());
                    if (locationAvailability.isLocationAvailable()) {
                        if (ActivityCompat.checkSelfPermission(InitActivity.this.getApplicationContext(),
                                android.Manifest.permission.ACCESS_FINE_LOCATION)
                                == PackageManager.PERMISSION_GRANTED) {
                            Task<Location> locationTask = fusedLocationProviderClient.getLastLocation();
                            locationTask.addOnCompleteListener(new OnCompleteListener<Location>() {
                                @Override
                                public void onComplete(@NonNull Task<Location> task) {
                                    Location location = task.getResult();                                    
                                }
                            });
                        } else {
                            requestLocationPermissions ();
                        }

                    } else {
fusedLocationProviderClient.requestLocationUpdates(locationRequest, pendingIntent);

                    }

                }
            });
        } else {
            requestLocationPermissions ();
        }

来源：https://stackoverflow.com/questions/50047863/fusedlocationproviderclient-lastlocation-addonsuccesslistener-always-null