为什么我的位置在第一次尝试时返回null

Question

当我第一次安装我的应用程序时，它总是返回null Location，但如果任何其他应用程序使用Location，那么我会重新运行该应用程序，然后我的应用可以获得我的位置地址。如何从第一次运行成功更新位置

//这是我的代码

public class UserinfoActivity extends AppCompatActivity implements LocationListener {
private Button button;
private EditText editText_pin, editText_mobile, editText_address;
DatabaseReference databaseReference;
MyPreferences myPreferences;
FusedLocationProviderClient fusedLocationProviderClient;
private static final int REQUEST_CODE = 101;
Location currentLocation;
Intent intentThatCalled;
public double latitude;
public double longitude;
public LocationManager locationManager;
public Criteria criteria;
public String bestProvider;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_userinfo);
databaseReference = FirebaseDatabase.getInstance().getReference("user_responses");
myPreferences = MyPreferences.getPreferences(this);
fusedLocationProviderClient= LocationServices.getFusedLocationProviderClient(this);
intentThatCalled = getIntent();
getLocation();
//optional_check
if ( ContextCompat.checkSelfPermission( this, android.Manifest.permission.ACCESS_COARSE_LOCATION ) != PackageManager.PERMISSION_GRANTED ) {
ActivityCompat.requestPermissions( this, new String[] {  android.Manifest.permission.ACCESS_COARSE_LOCATION  },
REQUEST_CODE);
}
Task<Location> task=fusedLocationProviderClient.getLastLocation();
task.addOnSuccessListener(new OnSuccessListener<Location>() {
@Override
public void onSuccess(Location location) {
if(location!=null){
currentLocation=location;
}
}
});
public static boolean isLocationEnabled(Context context) {
//...............
return true;
}
protected void getLocation() {
if (isLocationEnabled(UserinfoActivity.this)) {
locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
criteria = new Criteria();
bestProvider = String.valueOf(locationManager.getBestProvider(criteria, true)).toString();
//You can still do this if you like, you might get lucky:
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;
}
Location location = locationManager.getLastKnownLocation(bestProvider);
if (location != null) {
Log.e("TAG", "GPS is on");
Double latitude = location.getLatitude();
float float_latitude = latitude.floatValue();
myPreferences.setlatitude(float_latitude);
Double longitude = location.getLongitude();
float float_longitude = longitude.floatValue();
myPreferences.setlongitude(float_longitude);

/*Toast.makeText(MainActivity.this, "latitude:" + latitude + " longitude:" + longitude, Toast.LENGTH_SHORT).show();
searchNearestPlace(voice2text);*/
}
else{
//This is what you need:
locationManager.requestLocationUpdates(bestProvider, 1000, 0, this);
}
}
else
{
//prompt user to enable location....
//.................
}
}
@Override
protected void onPause() {
super.onPause();
locationManager.removeUpdates(this);
}
@Override
public void onLocationChanged(Location location) {
locationManager.removeUpdates(this);
//open the map:
latitude = location.getLatitude();
longitude = location.getLongitude();
/*Toast.makeText(MainActivity.this, "latitude:" + latitude + " longitude:" + longitude, Toast.LENGTH_SHORT).show();
searchNearestPlace(voice2text);*/
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
}
}

Answer 1

此链接可能会对您有所帮助http://shaoniiuc.com/android/android-receiving-location-updates-kotlin/

我假设您的清单中已经有COARSE和FINE位置

或者类似的东西：

Log.d("Find Location", "in find_location");
this.con = con;
String location_context = Context.LOCATION_SERVICE;
locationManager = (LocationManager) con.getSystemService(location_context);
List<String> providers = locationManager.getProviders(true);
for (String provider : providers) {
locationManager.requestLocationUpdates(provider, 1000, 0,
new LocationListener() {
public void onLocationChanged(Location location) {}
public void onProviderDisabled(String provider) {}
public void onProviderEnabled(String provider) {}
public void onStatusChanged(String provider, int status,
Bundle extras) {}
});
Location location = locationManager.getLastKnownLocation(provider);
if (location != null) {
latitude = location.getLatitude();
longitude = location.getLongitude();
addr = ConvertPointToLocation(latitude, longitude);
String temp_c = SendToUrl(addr);
}
}
}

从任何方法调用此。

来源：https://stackoverflow.com/a/9873478/13319579