手机重启后Android获取位置为空

Question

在我的应用程序中，我通过此功能获取手机的位置，但是当我重新启动手机并启动应用程序时，我从该方法中得到 null。我有什么遗漏或做错了吗？我应该怎么做才能解决这个问题？

这是我使用的函数：

public void getAddress() {
        Log.v("--", "get address 1");
        boolean isGPSProviderEnabled = locationManager
                .isProviderEnabled(LocationManager.GPS_PROVIDER);
        boolean network_enabled = locationManager
                .isProviderEnabled(LocationManager.NETWORK_PROVIDER);
        Log.v("--", "get address 31 " + isGPSProviderEnabled + " gps  -  "
                + isConnectedToNetwork());

        if (isGPSProviderEnabled || network_enabled) {
            Log.v("--", "get address 2");
            Criteria c = new Criteria();
            Log.v("--", "provider " + locationManager.getBestProvider(c, true));
            locationManager.requestSingleUpdate(
                    locationManager.getBestProvider(c, true),
                    mLocationListener, Looper.myLooper());
            location = locationManager.getLastKnownLocation(locationManager
                    .getBestProvider(c, true));
            if (location == null) {
                Log.v("--", "get address 6");
                // TODO check if this is working
                locationManager.requestSingleUpdate(
                        locationManager.getBestProvider(c, true),
                        mLocationListener, Looper.myLooper());
                locationManager.requestLocationUpdates(
                        locationManager.getBestProvider(c, true), 0, 0,
                        mLocationListener);
                Location oldLocation = new Location("");
                oldLocation.setLatitude(new Double(prefs.getString(
                        Constants.LATITUDE, "48.51")));
                oldLocation.setLongitude(new Double(prefs.getString(
                        Constants.LONGITUDE, "2.20")));
                populateList(oldLocation);
                // locationManager.requestLocationUpdates(
                // locationManager.getBestProvider(c, true), 1000, 100,
                // mLocationListener);
            } else {
                Log.v("--", "get address 3");
                if (isConnectedToNetwork()) {
                    new AsyncTask<Void, Void, Void>() {
                        protected Void doInBackground(Void... params) {
                            try {
                                com.quanticapps.athan.utils.Geocoder geocoder = new com.quanticapps.athan.utils.Geocoder(
                                        Main.this);
                                GeocoderModel geocoderModel = geocoder
                                        .getFromLocation(
                                                location.getLatitude(),
                                                location.getLongitude(), 5);
                                city = geocoderModel.getCity();
                                country = geocoderModel.getCountry();
                                prefs.edit().putString(Constants.CITY, city)
                                        .apply();
                                Log.v("--", "get address 4");
                            } catch (IOException e) {
                                Log.v("--", "get address 11");
                                e.printStackTrace();
                            } catch (LimitExceededException e) {
                                Log.v("--", "get address 12");
                                e.printStackTrace();
                            }
                            return null;
                        };

                        protected void onPostExecute(Void result) {
                            prefs.edit().putString(Constants.COUNTRY, country)
                                    .apply();
                            prefs.edit().putString(Constants.CITY, city)
                                    .apply();
                            populateList(location);
                        };
                    }.execute();
                } else {
                    city = null;
                    Log.v("--", "get address 33 " + location.getLatitude());
                    populateList(location);
                }
            }
        } else {
            Log.v("--", "get address 5");
            startGpsEnableDialog();
        }

    }

还有我的位置监听器：

private final LocationListener mLocationListener = new LocationListener() {
        @Override
        public void onLocationChanged(final Location location) {
            // TODO
            Log.v("--", "get address 121");
            if (location != null) {
                Main.this.location = location;
                getAddress();
            }
        }

        @Override
        public void onStatusChanged(String provider, int status, Bundle extras) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onProviderEnabled(String provider) {
            // TODO Auto-generated method stub
            Log.v("--", "provider enabled");
        }

        @Override
        public void onProviderDisabled(String provider) {
            // TODO Auto-generated method stub
            Log.v("--", "provider disabled");
        }
    };

Answer 1

当手机重新启动时，缓存的最后一个位置会丢失，所以如果你没有打开一个使用 GPS 的应用程序，如谷歌地图或其他东西，那么将没有最后一个位置。

永远不必将位置返回给您，您应该始终假设它可能为空

Answer 2

如果fusedLocationClient返回空位置，那么您应该使用requestLocationUpdates自己获取位置

    fusedLocationClient.lastLocation
        .addOnSuccessListener { location: Location? ->
            if (location == null) {
                checkLocationSettingsAndStartLocationUpdates(
                    resolutionForResult
                )
            } else {
                showUserCurrentLocation(location)
            }
        }

首先让我们定义resolutionForResult

private val resolutionForResult =
    registerForActivityResult(ActivityResultContracts.StartIntentSenderForResult()) { activityResult ->
        if (activityResult.resultCode == RESULT_OK)
            locationManger.startLocationUpdates(requestPermissionLauncher)
        else {
            showMessage("we can't determine your location")
        }
    }

那么这个方法

private fun checkLocationSettingsAndStartLocationUpdates(
    resolutionForResult: ActivityResultLauncher<IntentSenderRequest>
) {
    val builder = LocationSettingsRequest.Builder()
        .addLocationRequest(locationRequest)
    val client: SettingsClient = LocationServices.getSettingsClient(requireContext)
    val task: Task<LocationSettingsResponse> = client.checkLocationSettings(builder.build())

    task.addOnSuccessListener { _ ->
        startLocationUpdates()
    }

    task.addOnFailureListener { exception ->
        if (exception is ResolvableApiException) {
            // Location settings are not satisfied, but this can be fixed
            // by showing the user a dialog.
            try {
                val intentSenderRequest =
                    IntentSenderRequest.Builder(exception.resolution).build()
                resolutionForResult.launch(intentSenderRequest)
            } catch (sendEx: IntentSender.SendIntentException) {
            }
        }
    }
}

然后是startLocationUpdates 实际位置更新发生的地方

fun startLocationUpdates(
    ) {
        if (ActivityCompat.checkSelfPermission(
                requireContext,
                Manifest.permission.ACCESS_FINE_LOCATION
            ) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(
                requireContext,
                Manifest.permission.ACCESS_COARSE_LOCATION
            ) != PackageManager.PERMISSION_GRANTED
        ) {
            requestPermissionLauncher.launch(
                Manifest.permission.ACCESS_FINE_LOCATION
            )
            return
        }
        fusedLocationClient.requestLocationUpdates(
            locationRequest,
            locationCallback,
            Looper.getMainLooper()
        )
    }

这里也是locationRequest和locationCallback的声明

private val locationRequest: LocationRequest by lazy {
    LocationRequest.create().apply {
        interval = 10000
        fastestInterval = 5000
        priority = LocationRequest.PRIORITY_HIGH_ACCURACY
    }
}

和

private var locationCallback: LocationCallback = object : LocationCallback() {
    override fun onLocationResult(locationResult: LocationResult?) {
        locationResult ?: return
        for (location in locationResult.locations) {
            if (location != null) {
                //showUserCurrentLocation(location)
                stopLocationUpdates(this)//if you only need the location once then stop the updates
                break
            }
        }
    }
}

这里是stopLocationUpdates方法

fun stopLocationUpdates(locationCallback: LocationCallback) {
    fusedLocationClient.removeLocationUpdates(locationCallback)
}

fusedLocationClient 也是在用户授予权限或检查权限后定义的，

这是检查是否保证权限的方法

fun locationPermissionGranted(): Boolean {
    return when (PackageManager.PERMISSION_GRANTED) {
        ContextCompat.checkSelfPermission(
            requireContext,
            Manifest.permission.ACCESS_FINE_LOCATION
        ) -> {
            fusedLocationClient =
                LocationServices.getFusedLocationProviderClient(requireContext)
            true
        }
        else -> {
            false
        }
    }
}

如果是假的，那么你需要请求许可

 requestPermission(requestPermissionLauncher: ActivityResultLauncher<String>) {
        requestPermissionLauncher.launch(
            Manifest.permission.ACCESS_FINE_LOCATION
        )
    }

这是requestPermissionLauncher的定义

private val requestPermissionLauncher = registerForActivityResult(
    ActivityResultContracts.RequestPermission()
) { isGranted: Boolean ->
    if (isGranted) {
        fusedLocationClient =
                LocationServices.getFusedLocationProviderClient(requireContext())
    } else {
        showMessage(
            "the application can't show your " +
                    "current location on the map, because you denied the location permission"
        )
    }
}