LocationManager still cant find last known location after GPS is turned on

问题

I'm having a problem with android where even after the user turns their location service on, the LocationManager still can't find the users location.

Before I launch the activity that needs to use the user's location I call the following:

//Menu Activity
LocationManager lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
if(lm.isProviderEnabled(LocationManager.GPS_PROVIDER){
    Intent nearby = new Intent(mActivityContext, NearbyActivity.class);
    startActivity(nearby);
}else{
    alertNoGps();
}

Once GPS is turned on the nearby activity can be launched, but the LocationManager still cannot find the users last known location. My relevant code for this is:

//Nearby Activity
try{
    LocationManager locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
    Location location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
    if(location != null){
        ...
    }else{
        Toast.makeText ...
    }
} catch(SecurityException e){
    e.printStackTrace();
}

The phone I'm currently testing on is running Android Marshmallow 6.0.1. If the GPS is already turned on before the app is run through android studio then I have no problem getting the last known location. It's only when the GPS is turned off before I run the app and turn it on while the app is running that I have problems. What about LocationManger is causing this?

Edit: Also in the manifest I have both Fine and Coarse location permissions. I do not know if this is an issue with API 23 and above because of the extra permission checks required, but I have to imagine they are still handled by the Security Exception.

回答1:

There are two different ways to retrieve the location, one is based on network and another is based on GPS services. Certainly, location based on GPS services would always be more accurate. According to the documentation, it might take some time to receive the location using the GPS services. In this case, the last known location can be used to get the recently available location by using getLastKnownLocation() method. Here, to get the last available location, you should change LocationManager.GPS_PROVIDER to LocationManager.NETWORK_PROVIDER.

And if you wish to receive the accurate, real time location based on GPS services, I recommend you to use FusedLocationApi. You can find it here https://developer.android.com/training/location/receive-location-updates.html

Cheers..!!

回答2:

This is exactly how it should work. Android clears the last known location for a provider when it is disabled, and will return null until a new point is polled for that provider.

In your situation, I would recommend that if you get null location point for last known location with GPS, just request for a single update.

回答3:

I found out that similar to Pablo's answer, getLastKnownLocation() will be cleared and because it is a rather casual function can return null quite often. If GPS coordinates are more demanded, then you should be more forceful when trying to get GPS coordinates and use something like requestLocationUpdates() or Google's FusedLocationApi rather than getLastKnownLocation().

So now I am using FusedLocationApi with a GoogleApiClient I built using:

client = new GoogleApiClient.Builder(mActivityContext) 
                .addApi(LocationServices.API)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .build();

After the client is connected I find the GPS location in the onConnected() method override which looks like:

LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
Location location = LocationServices.FusedLocationApi.getLastLocation(client);

This seems to be much more reliable in finding GPS coordinates.

来源：https://stackoverflow.com/questions/43198655/locationmanager-still-cant-find-last-known-location-after-gps-is-turned-on

标签

android

geolocation

gps

android-location

locationmanager