java - 当我读取 GPS 位置时 Android 返回 null

Question

我正在尝试使用此代码读取我的 Android 设备的位置，但它在经度和纬度上返回 null，尽管我添加了正确的权限，并且在启用 GPS 的情况下在我的 Android 设备上进行了尝试。我试图找出问题所在，发现这个if语句不成立

 if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {

我尝试将 != 更改为 == 它也不起作用，如果我尝试删除此 if 语句，它会给我错误:调用需要可能被用户拒绝的权限:代码应显式检查权限是否可用(使用 checkPermission)或显式处理潜在的 SecurityException这是我的 GPS 代码:

public class GPSPosition extends Service implements LocationListener {
    private final Context mContext;

    // flag for GPS status
    boolean isGPSEnabled = false;

    // flag for network status
    boolean isNetworkEnabled = false;

    // flag for GPS status
    boolean canGetLocation = false;

    Location location; // location
    double latitude; // latitude
    double longitude; // longitude

    // The minimum distance to change Updates in meters
    private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10; // 10 meters

    // The minimum time between updates in milliseconds
    private static final long MIN_TIME_BW_UPDATES = 100 * 60*1; // 60 seconds

    // Declaring a Location Manager
    protected LocationManager locationManager;

    public GPSPosition(Context context) {
        this.mContext = context;
        getLocation();
    }

    public Location getLocation() {
        try {
            locationManager = (LocationManager) mContext
                    .getSystemService(LOCATION_SERVICE);

            // getting GPS status
            isGPSEnabled = locationManager
                    .isProviderEnabled(LocationManager.GPS_PROVIDER);

            // getting network status
            isNetworkEnabled = locationManager
                    .isProviderEnabled(LocationManager.NETWORK_PROVIDER);

            if (!isGPSEnabled && !isNetworkEnabled) {
                // no network provider is enabled
            } else {
                this.canGetLocation = true;
                // First get location from Network Provider
                if (isNetworkEnabled) {

                    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
                        Log.d("enabless1", "Network");
                        locationManager.requestLocationUpdates(
                                LocationManager.NETWORK_PROVIDER,
                                MIN_TIME_BW_UPDATES,
                                MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                        Log.d("Network", "Network");
                        if (locationManager != null) {
                            location = locationManager
                                    .getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
                            if (location != null) {
                                latitude = location.getLatitude();
                                longitude = location.getLongitude();
                            }
                        }
                    }
                }
                // if GPS Enabled get lat/long using GPS Services
                if (isGPSEnabled) {
                    if (location == null) {
                        locationManager.requestLocationUpdates(
                                LocationManager.GPS_PROVIDER,
                                MIN_TIME_BW_UPDATES,
                                MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                        Log.d("GPS Enabled", "GPS Enabled");
                        if (locationManager != null) {
                            location = locationManager
                                    .getLastKnownLocation(LocationManager.GPS_PROVIDER);
                            if (location != null) {
                                latitude = location.getLatitude();
                                longitude = location.getLongitude();
                            }
                        }
                    }
                }
            }

        } catch (Exception e) {
            e.printStackTrace();
        }

        return location;
    }
    public double getLatitude(){
        if(location != null){
            latitude = location.getLatitude();
        }

        // return latitude
        return latitude;
    }

    /**
     * Function to get longitude
     * */
    public double getLongitude(){
        if(location != null){
            longitude = location.getLongitude();
        }

        // return longitude
        return longitude;
    }
    public boolean canGetLocation() {
        return this.canGetLocation;
    }

    /**
     * Function to show settings alert dialog
     * */
    public void showSettingsAlert(){
        AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);

        // Setting Dialog Title
        alertDialog.setTitle("GPS is settings");

        // Setting Dialog Message
        alertDialog.setMessage("GPS is not enabled. Do you want to go to settings menu?");

        // Setting Icon to Dialog
        //alertDialog.setIcon(R.drawable.delete);

        // On pressing Settings button
        alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog,int which) {
                Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
                mContext.startActivity(intent);
            }
        });

        // on pressing cancel button
        alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                dialog.cancel();
            }
        });

        // Showing Alert Message
        alertDialog.show();
    }




    public void onLocationChanged(Location location) {

        //  Toast.makeText(mContext, "log:" + Double.toString(location.getLongitude()) + ", lat: " + Double.toString(location.getLatitude()), Toast.LENGTH_LONG).show();
    }

    @Override
    public void onProviderDisabled(String provider) {
    }

    @Override
    public void onProviderEnabled(String provider) {
    }

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

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }
}

这里我在 MainActivity 中调用它们:

public class MainActivity extends AppCompatActivity {

    public static String lat="10";
    public static String lang="10";
    GPSPosition gps;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

//        Toast.makeText(MainActivity.this, lat + " " + lang, Toast.LENGTH_SHORT).show();
        gps = new GPSPosition(MainActivity.this);

    }

    public void clickingBtn(View view) {



        if (gps.canGetLocation()) {

            double latitude = gps.getLatitude();
            lat = String.valueOf(latitude);
            double longitude = gps.getLongitude();
            lang = String.valueOf(longitude);
            Toast.makeText(MainActivity.this, latitude + " " + longitude, Toast.LENGTH_SHORT).show();
        } else {

            gps.showSettingsAlert();
        }

    }

这是 list 中的权限:

<uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

Answer 1

如果该提供商没有最近的位置数据，

getLastKnownLocation() 将返回 null。而且，即使它返回 null 以外的内容，Location 也可能相当旧。如果 getLastKnownLocation() 返回不可用的内容，您必须等到 onLocationChanged() 被调用，然后使用传递给该值的 Location方法。