如何获取设备位置

Question

So, I'm trying to build a weather app for practice and I've been running into the problem of trying to get the location. I've read people suggest to use getLastLocation through the fused location API, problem with that is if they don't already have a location registered on the device it comes up null. I've noticed using the emulator times that this come up is rare, but I'd still like my app to handle it properly. One instance where you might run into this is if they just turned GPS off and back on, or if the phone was just turned on. One thing I did was if getLastLocation does come back null, is to request an update, but then you still have to wait for the device to register an updated location, which with a weather app all of the data is based off of and you're still kind of running into the same problem. I've noticed with other apps this isn't a problem, like sometimes I actually have to load up Google Maps to get it to register a location. How does Google Maps force it to update the location? Here's the example from my getLocation method:

public void getLocation() throws SecurityException {
    boolean gps_enabled;
    LocationManager lm = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
    gps_enabled = lm.isProviderEnabled(LocationManager.GPS_PROVIDER);
    if (gps_enabled) {

        Location location = LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient);
        if (location != null) {
            startGetForecast(location);
        } else {
            LocationRequest request = LocationRequest.create();
            request.setNumUpdates(1);
            request.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
            LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, request, this);
        }
    } 
    else {
        AlertDialogFragment alertDialogFragment = new AlertDialogFragment();
        alertDialogFragment.setErrorTexts("Location Unavailable", "Could not retrieve location information.", "Exit");
        alertDialogFragment.show(getSupportFragmentManager(), "Location Unavailable");
    }
}

Answer 1

Note: This answer could sound like not answering to the question directly but after chatting (comments in question) with OP as his code was ok in general but the condition around the problem, this answer has satisfied OP.

Fortunately, the standard library Is not the only way Google can get code into your hands. In addition to the standard library, Google provider Play services. This is a set of common services that are installed alongside the Google Play store application. To fix this location mess, Google shipped a new locations services in Play Services called the Fused Location Provider.

Since these libraries live in another application, you must actually have that application installed. This means that only devices with the Play Store app installed and up to date will be able to use your application.

So the conclusion is:

1. You need to test the app on your device as mentioned above.

2. Since you are using Fused Location Provider Api, that means the Api will automatically determine last location from one of the following sources:

   1. GPS radio
   2. Coarse points from cell towers
   3. WiFi connections

3. So you could easily remove the GPS if condition from your code

4. Be a ware of that if you must use GPS signal, you need to be out side the building, lab, home or office.

If you want to dig more find more in the mentioned resources and there is a lot of online resources.

Resources: The first part of the answer, the source of it is from:

Android Programming: The Big Nerd Ranch Guide
2nd edition
chapter 31 page 552 under Google Play Services