Как создать приложение, в котором сервисы приложения всегда работают в фоновом режиме, даже если приложение закрыто в Xamarin (Android)?

Пожалуйста, обратитесь к приведенному ниже образцу. Вы можете использовать диспетчер тревог для перезапуска службы.

Пожалуйста, следуйте инструкциям.

Шаг 1: Создание BroadcastReceiver

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;

namespace AlarmManagerApp
{
    [BroadcastReceiver(Enabled = true)]
    [IntentFilter(new[] { Android.Content.Intent.ActionBootCompleted })]
    class AlarmReceiver : BroadcastReceiver
    {
        Context context;
        public override void OnReceive(Context context, Intent intent)
        {
            this.context = context;
            Toast.MakeText(context,"Recieved",ToastLength.Long).Show();
            Intent background = new Intent(context, typeof(BackgroundService));
            context.StartService(background);

        }
    }
}

Шаг 2: Добавьте AlarmManager в MainActivity, где вы хотите вызвать службу

namespace AlarmManagerApp
{
    [Activity(Label = "@string/app_name", Theme = "@style/AppTheme.NoActionBar", MainLauncher = true)]
    public class MainActivity : AppCompatActivity
    {
        String alarm = Context.AlarmService;
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.activity_main);

            Android.Support.V7.Widget.Toolbar toolbar = FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar);
            SetSupportActionBar(toolbar);

            var alarmIntent = new Intent(this, typeof(AlarmReceiver));
            alarmIntent.PutExtra("title", "Hello");
            alarmIntent.PutExtra("message", "World!");

            var pending = PendingIntent.GetBroadcast(this, 0, alarmIntent, PendingIntentFlags.UpdateCurrent);

            var alarmManager = GetSystemService(AlarmService).JavaCast<AlarmManager>();
            alarmManager.SetRepeating(AlarmType.ElapsedRealtime,DateTime.Now.Millisecond,  5 * 100, pending);


          }
   }

Шаг 3: Добавить службу

namespace AlarmManagerApp
{
    [Service]
    public class BackgroundService : Service
    {
        public override void OnCreate()
        {
            base.OnCreate();

        }

        public override StartCommandResult OnStartCommand(Intent intent, StartCommandFlags flags, int startId)
        {
            Log.Debug("service","Service Started");
            //init the handler in oncreate
            System.Timers.Timer Timer1 = new System.Timers.Timer();
            Timer1.Start();
            Timer1.Interval = 3000;
            int a = 0;
            Timer1.Enabled = true;
            //Timer1.Elapsed += OnTimedEvent;
            Timer1.Elapsed += (object sender, System.Timers.ElapsedEventArgs e) =>
            {
                Timer1.Stop();
                Timer1.Start();
                a++;
               //Delete time since it will no longer be used.
                Timer1.Dispose();
            };
            Timer1.Start();

            return StartCommandResult.Sticky;
        }

        public override IBinder OnBind(Intent intent)
        {
            return null;
        }

        public override void OnTaskRemoved(Intent rootIntent)
        {
            Intent restartServiceIntent = new Intent(this, this.Class);
            restartServiceIntent.SetPackage(this.PackageName);
            Log.Debug("service", "Service Restarted");

            PendingIntent restartServicePendingIntent = PendingIntent.GetService(this, 1, restartServiceIntent, PendingIntentFlags.OneShot);
            AlarmManager alarmService = (AlarmManager)this.GetSystemService(Context.AlarmService);

            alarmService.SetRepeating(AlarmType.RtcWakeup, SystemClock.CurrentThreadTimeMillis(), 30 * 1000, restartServicePendingIntent);
            NotificationManager notificationManager =
                (NotificationManager)GetSystemService(NotificationService);

            Notification.Builder builder = new Notification.Builder(this);
            Intent notificationIntent = new Intent(this, typeof(MainActivity));
            PendingIntent contentIntent = PendingIntent.GetActivity(this, 0, notificationIntent, 0);

            //set
            builder.SetContentIntent(contentIntent);
            builder.SetSmallIcon(Resource.Mipmap.ic_launcher);
            builder.SetContentText("Contents");
            builder.SetContentTitle("title");
            builder.SetAutoCancel(true);
            builder.SetDefaults(NotificationDefaults.All);


            notificationManager.Notify(1, builder.Build());

            base.OnTaskRemoved(rootIntent);
        }
    }
}

Это также работает, если приложение закрыто и устройство перезапущено.