getLastKnownLocation始终返回null。 请解释？

Question

您能否解释一下为什么getLastKnownLocation总是返回null？

这是onCreate方法：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

    provider = locationManager.getBestProvider(new Criteria(), false);

    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
        // TODO: Consider calling
        //    ActivityCompat#requestPermissions
        // here to request the missing permissions, and then overriding
        //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
        //                                          int[] grantResults)
        // to handle the case where the user grants the permission. See the documentation
        // for ActivityCompat#requestPermissions for more details.
        return;
    }

    locationManager.requestLocationUpdates(provider, 400, 1, this);

    Location location = locationManager.getLastKnownLocation(provider);

    if (location != null) {
        Log.i("Location info", "location achieved");
    } else
        Log.i("Location info", "location failed");


}

日志显示：

04-25 19:13:03.437 11755-11755/com.example.saurabh.locationdemo E/MultiWindowProxy: getServiceInstance failed!

04-25 19:13:03.462 11755-11755/com.example.saurabh.locationdemo I/Location info: location failed

我正在我的设备上测试该应用，并已在该设备上启用Google位置信息。

Answer 1

我遇到了同样的问题，没有显示任何延迟，并且收到了相同的消息：

E / MultiWindowProxy：getServiceInstance失败！

为我解决的是转到智能手机的Settings ，“ Apps子菜单，然后找到我的应用。 然后转到权限并手动允许提供我的位置。

Answer 2

好的，请参阅下面的代码，这些代码在许多应用程序中都已使用（并且运行良好），应该可以为您设定正确的方向。 今天是我第一次在StackOverflow上发布答案，所以如果我还没有足够的解释，请不要解雇我，希望代码能不言自明？

 public boolean getLocation(Context context, LocationResult result)
{

    locationResult=result;
    if(lm==null)
        lm = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);

try{gps_enabled=lm.isProviderEnabled(LocationManager.GPS_PROVIDER);}catch(Exception ex){}
    try{network_enabled=lm.isProviderEnabled(LocationManager.NETWORK_PROVIDER);}catch(Exception ex){}

    if(!gps_enabled && !network_enabled)
        return false;

    if(gps_enabled)
        lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListenerGps);
    if(network_enabled)
        lm.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locationListenerNetwork);
    timer1=new Timer();


    timer1.schedule(new GetLastLocation(), 10000);
    return true;
}

LocationListener locationListenerGps = new LocationListener() {
    public void onLocationChanged(Location location) {
        timer1.cancel();
        locationResult.gotLocation(location);
        lm.removeUpdates(this);
        lm.removeUpdates(locationListenerNetwork);
    }
    public void onProviderDisabled(String provider) {}
    public void onProviderEnabled(String provider) {}
    public void onStatusChanged(String provider, int status, Bundle extras) {}
};

LocationListener locationListenerNetwork = new LocationListener() {
    public void onLocationChanged(Location location) {
        timer1.cancel();
        locationResult.gotLocation(location);
        lm.removeUpdates(this);
        lm.removeUpdates(locationListenerGps);
    }
    public void onProviderDisabled(String provider) {}
    public void onProviderEnabled(String provider) {}
    public void onStatusChanged(String provider, int status, Bundle extras) {}
};

class GetLastLocation extends TimerTask {
    @Override

    public void run() {


         Location net_loc=null, gps_loc=null;
         if(gps_enabled)
             gps_loc=lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
         if(network_enabled)
             net_loc=lm.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);

         if(gps_loc!=null && net_loc!=null){
             if(gps_loc.getTime()>net_loc.getTime())
                 locationResult.gotLocation(gps_loc);
             else
                 locationResult.gotLocation(net_loc);
             return;
         }

         if(gps_loc!=null){
             locationResult.gotLocation(gps_loc);
             return;
         }
         if(net_loc!=null){
             locationResult.gotLocation(net_loc);
             return;
         }
         //locationResult.gotLocation(null);
    }
}