MainActivity.cs

using Android.App;
using Android.Content.PM;
using Android.Runtime;
using Android.OS;
using FFImageLoading.Forms.Platform;
using Plugin.CurrentActivity;
using Android.Content;

using Android.Gms.Common;
using Android;
using Xamarin.Essentials;

namespace Barber.Droid
{
    [Activity(Label = "Barber", Icon = "@mipmap/icon", Theme = "@style/MainTheme", MainLauncher = false, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation)]
    public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
    {
        internal static readonly string CHANNEL_ID = "my_notification_channel";
        internal static readonly int NOTIFICATION_ID = 100;

        protected override void OnCreate(Bundle savedInstanceState)
        {
            TabLayoutResource = Resource.Layout.Tabbar;
            ToolbarResource = Resource.Layout.Toolbar;

            base.OnCreate(savedInstanceState);

            CachedImageRenderer.Init(true);
            CrossCurrentActivity.Current.Init(this, savedInstanceState);
            Xamarin.FormsMaps.Init(this, savedInstanceState);
            Firebase.FirebaseApp.InitializeApp(this);
            Rg.Plugins.Popup.Popup.Init(this, savedInstanceState);
            Xamarin.Essentials.Platform.Init(this, savedInstanceState);
            global::Xamarin.Forms.Forms.Init(this, savedInstanceState);
            
            LoadApplication(new App());

            if (Intent.Extras != null)
            {
                foreach (var key in Intent.Extras.KeySet())
                {
                    var value = Intent.Extras.GetString(key);
                }
            }

            IsPlayServicesAvailable();
            CreateNotificationChannel();
        }
        protected override void OnStart()
        {
            base.OnStart();

            if ((int)Build.VERSION.SdkInt >= 23)
            {
                if (CheckSelfPermission(Manifest.Permission.AccessFineLocation) != Permission.Granted)
                {
                    //RequestPermissions(LocationPermissions, RequestLocationId);
                }
            }
        }
        public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Android.Content.PM.Permission[] grantResults)
        {
            Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);

            base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
        }
        public bool IsPlayServicesAvailable()
        {
            int resultCode = GoogleApiAvailability.Instance.IsGooglePlayServicesAvailable(this);
            if (resultCode != ConnectionResult.Success)
            {
                if (!GoogleApiAvailability.Instance.IsUserResolvableError(resultCode))
                    Finish();
                return false;
            }
            else
            {
                return true;
            }
        }

        public override void OnBackPressed()
        {
            if (Rg.Plugins.Popup.Popup.SendBackPressed(base.OnBackPressed))
            {
                // Do something if there are some pages in the `PopupStack`
            }
            else
            {
                // Do something if there are not any pages in the `PopupStack`
            }
        }

        void CreateNotificationChannel()
        {
            if (Build.VERSION.SdkInt < BuildVersionCodes.O)
            {
                // Notification channels are new in API 26 (and not a part of the
                // support library). There is no need to create a notification
                // channel on older versions of Android.
                return;
            }

            var channel = new NotificationChannel(CHANNEL_ID,
                                                  "FCM Notifications",
                                                  NotificationImportance.High)
            {

                Description = "Firebase Cloud Messages appear in this channel"
            };

            var notificationManager = (NotificationManager)GetSystemService(Android.Content.Context.NotificationService);
            notificationManager.CreateNotificationChannel(channel);
        }
    }
}