Recopilación de coordenadas GPS

Estoy construyendo una aplicación nativa de Android usando xamarin. El problema es que la aplicación recopila y muestra las coordenadas perfectamente en el emulador, pero cuando lo pongo en un teléfono inteligente (probé 2 teléfonos Samsung) aparece y no puedo determinar la dirección actual. Los datos y las ubicaciones de información adicional están activados, por lo que no estoy seguro de dónde está el problema. Gracias por tu ayuda. Aquí está la receta de xammarin encase que ayudahttps://developer.xamarin.com/recipes/android/os_device_resources/gps/get_current_device_location/

    [Activity(Label = "NewRoute")]
    public class NewRouteActivity : Activity, ILocationListener
    {

        static readonly string TAG = "X:" + typeof(NewRouteActivity).Name;
        TextView _addressText;
        Location _currentLocation;
        LocationManager _locationManager;

        string _locationProvider;
        TextView _locationText;


        public async void OnLocationChanged(Location location) {
            _currentLocation = location;
            if (_currentLocation == null)
            {
                _locationText.Text = "Unable to determine your location. Try again in a short while.";
            }
            else
            {
                _locationText.Text = string.Format("{0:f6},{1:f6}", _currentLocation.Latitude, _currentLocation.Longitude);
                Address address = await ReverseGeocodeCurrentLocation();
                DisplayAddress(address);
            }
        }

        public void OnProviderDisabled(string provider) { }

        public void OnProviderEnabled(string provider) { }

        public void OnStatusChanged(string provider, Availability status, Bundle extras) { }

        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);
            SetContentView(Resource.Layout.CreatetRoute);

            _addressText = FindViewById<TextView>(Resource.Id.address_text);
            _locationText = FindViewById<TextView>(Resource.Id.location_text);
            FindViewById<TextView>(Resource.Id.get_address_button).Click += AddressButton_OnClick;

            InitializeLocationManager();


            Button btnEndPoint = FindViewById<Button>(Resource.Id.btnEndPoint);
            btnEndPoint.Click += new EventHandler(AfterPointsCollected);
        }
        //Location Stuff
        void InitializeLocationManager()
        {
            _locationManager = (LocationManager)GetSystemService(LocationService);
            Criteria criteriaForLocationService = new Criteria
            {
                Accuracy = Accuracy.Fine
            };
            IList<string> acceptableLocationProviders = _locationManager.GetProviders(criteriaForLocationService, true);

            if (acceptableLocationProviders.Any())
            {
                _locationProvider = acceptableLocationProviders.First();
            }
            else
            {
                _locationProvider = string.Empty;
            }
            Log.Debug(TAG, "Using " + _locationProvider + ".");
        }
        //Override OnResume so that Activity1 will begin listening to the LocationManager when the activity comes into the foreground:
        protected override void OnResume()
        {
            base.OnResume();
            _locationManager.RequestLocationUpdates(_locationProvider, 0, 0, this);
        }
        async void AddressButton_OnClick(object sender, EventArgs eventArgs)
        {
            if (_currentLocation == null)
            {
                _addressText.Text = "Can't determine the current address. Try again in a few minutes.";
                return;
            }

            Address address = await ReverseGeocodeCurrentLocation();
            DisplayAddress(address);
        }

        async Task<Address> ReverseGeocodeCurrentLocation()
        {
            Geocoder geocoder = new Geocoder(this);
            IList<Address> addressList =
                await geocoder.GetFromLocationAsync(_currentLocation.Latitude, _currentLocation.Longitude, 10);

            Address address = addressList.FirstOrDefault();
            return address;
        }

        void DisplayAddress(Address address)
        {
            if (address != null)
            {
                StringBuilder deviceAddress = new StringBuilder();
                for (int i = 0; i < address.MaxAddressLineIndex; i++)
                {
                    deviceAddress.AppendLine(address.GetAddressLine(i));
                }
                // Remove the last comma from the end of the address.
                _addressText.Text = deviceAddress.ToString();
            }
            else
            {
                _addressText.Text = "Unable to determine the address. Try again in a few minutes.";
            }
        }

        //Override OnPause and unsubscribe Activity1 from the LocationManager when the activity goes into the background:
        protected override void OnPause()
        {
            base.OnPause();
            _locationManager.RemoveUpdates(this);
        }
        //Changing Activity
        void AfterPointsCollected(object sender, EventArgs e)
        {
            //context   //activity
            Intent intent = new Intent(this, typeof(AfterPointsCollectedActivity));
            //starts the activity with the intent above
            this.StartActivity(intent);

        }

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