无法在 Xamarin Android 8.1 API 27 上获取位置

Question

I'm Having problems when trying to get location on Android 8.1(API 27). Android 7.0(API 7.0), Android 9.0 and Android 10+ works properly but on Android 8.1(API 27) I get this error(debug or release mode):

Unable to get location: System.NullReferenceException: Object reference not set to an instance of an object
  at Project.Permissions.GetCurrentPosition () [0x000a9] in <f8798290f683423180c09ee7a2b0a8fa>:0

The relevant part of my code:

Project.Permissions class:

public class Permissions
{

  public async Task<bool> LocationPermission()
        {
            try
            {
                PermissionStatus Location = await new Permissions.LocationWhenInUse().CheckStatusAsync();
                if (Location == PermissionStatus.Granted)
                    return true;
                else
                {
                    PermissionStatus status = await new Permissions.LocationWhenInUse().RequestAsync();
                    if (status == PermissionStatus.Granted)
                        return true;
                    else
                        return false;
                }                
            }
            catch (Exception ex)
            {
                Console.WriteLine("Error =>" + ex.Message);
                return false;
            }
        }

public async Task<Position> GetCurrentPosition()
{
            Position position;
            try
            {

                var request = new GeolocationRequest(GeolocationAccuracy.Best);

                Location locator = await Geolocation.GetLastKnownLocationAsync();
                locator.Accuracy = 50;

                Location localNow = await Geolocation.GetLocationAsync(request);
                localNow.Accuracy = 50;

                if (localNow?.Latitude != null && localNow?.Longitude!=null)
                    position = new Position(localNow.Latitude, localNow.Longitude);
                else
                    position = new Position(locator.Latitude, locator.Longitude);
            }
            catch (FeatureNotSupportedException fnsEx)
            {
                position = new Position(0, 0);
                // Handle not supported on device exception
                Debug.WriteLine("Feature not supported => " +fnsEx);
            }
            catch (PermissionException pEx)
            {
                position = new Position(0, 0);
                // Handle permission exception
                Debug.WriteLine("Error => "+pEx);
            }
            catch (Exception ex)
            {
                position = new Position(0,0);
                Console.WriteLine("Unable to get location => " + ex);
            }
            return position;
     }
}

AndroidManifest:

<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

MainActivity:

public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Android.Content.PM.Permission[] grantResults)
{
    Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);
    PermissionsImplementation.Current.OnRequestPermissionsResult(requestCode, permissions, grantResults);
    base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
}

What I'm doing wrong?

Answer 1

The problem was in Location locator = await Geolocation.GetLastKnownLocationAsync();

It was trying to get last know location, but it didn't exists since the simulator device was being executed for the very first time, so it was returning NULL and causing System.NullReferenceException.