How to use an interface - xamarin

Question

I'm trying to build my first xamarin app, which I'm building using forms. One of the features of the app is sending users locations and have to do that even if the app is in the background. So I came across James Montemagno's GeolocatorPlugin, which promised to do just that.
As the documentation was not that clear on how to implement his plugin in the background I looked through the projects closed issues and found a guy which gave an example of a simple case of using the plugin with a service. (https://github.com/jamesmontemagno/GeolocatorPlugin/issues/272)
I've adopted the code and created the service. The service are using an interface to start the service and now my problem is how to make use of the interface to make the service run.
In my shared project I put the interface and the viewmodel and in xamarin.android project I put the service.
The interface - IGeolocationBackgroundService:
public interface IGeolocationBackgroundService {
void StartService();
void StartTracking();
}
The viewmodel - GeolocatorPageViewModel:
public class GeolocatorPageViewModel
{
public Position _currentUserPosition { get; set; }
public string CoordinatesString { get; set; }
public List<string> userPositions { get; set; }
public ICommand StartTrackingCommand => new Command(async () =>
{
if (CrossGeolocator.Current.IsListening)
{
await CrossGeolocator.Current.StopListeningAsync();
}
CrossGeolocator.Current.DesiredAccuracy = 25;
CrossGeolocator.Current.PositionChanged += Geolocator_PositionChanged;
await CrossGeolocator.Current.StartListeningAsync(
TimeSpan.FromSeconds(3), 5);
});
private void Geolocator_PositionChanged(object sender, PositionEventArgs e)
{
var position = e.Position;
_currentUserPosition = position;
var positionString = $"Latitude: {position.Latitude}, Longitude: {position.Longitude}";
CoordinatesString = positionString;
Device.BeginInvokeOnMainThread(() => CoordinatesString = positionString);
userPositions.Add(positionString);
Debug.WriteLine($"Position changed event. User position: {CoordinatesString}");
}
}
The service - GeolocationService:
[assembly: Xamarin.Forms.Dependency(typeof(GeolocationService))]
namespace MyApp.Droid.Services
{
[Service]
public class GeolocationService : Service, IGeolocationBackgroundService
{
Context context;
private static readonly string CHANNEL_ID = "geolocationServiceChannel";
public GeolocatorPageViewModel ViewModel { get; private set; }
public override IBinder OnBind(Intent intent)
{
return null;
}
public GeolocationService(Context context)
{
this.context = context;
CreateNotificationChannel();
}
private void CreateNotificationChannel()
{
NotificationChannel serviceChannel = new NotificationChannel(CHANNEL_ID,
"GeolocationService", Android.App.NotificationImportance.Default);
NotificationManager manager = context.GetSystemService(Context.NotificationService) as NotificationManager;
manager.CreateNotificationChannel(serviceChannel);
}
//[return: GeneratedEnum]
public override StartCommandResult OnStartCommand(Intent intent, [GeneratedEnum] StartCommandFlags flags, int startId)
{
var newIntent = new Intent(this, typeof(MainActivity));
newIntent.AddFlags(ActivityFlags.ClearTop);
newIntent.AddFlags(ActivityFlags.SingleTop);
var pendingIntent = PendingIntent.GetActivity(this, 0, newIntent, 0);
var builder = new Notification.Builder(this, CHANNEL_ID);
var notification = builder.SetContentIntent(pendingIntent)
.SetSmallIcon(Resource.Drawable.ic_media_play_light)
.SetAutoCancel(false)
.SetTicker("Locator is recording")
.SetContentTitle("GeolocationService")
.SetContentText("Geolocator is recording for position changes.")
.Build();
StartForeground(112, notification);
//ViewModel = new GeolocatorPageViewModel();
return StartCommandResult.Sticky;
}
public void StartService()
=> context.StartService(new Intent(context, typeof(GeolocationService)));
public void StartTracking()
{
ViewModel = new GeolocatorPageViewModel();
ViewModel.StartTrackingCommand.Execute(null);
}
}
}
So be clear, I need to start the service and I'm not used to interfaces, so how do I call the interface?

Answer 1

use DependencyService to get a reference to your service and then start it
var svc = DependencyService.Get<IGeolocationBackgroundService>();
svc.StartService();
svc.StartTracking();